typedef bfd
A BFD has type bfd; objects of this type are the
cornerstone of any application using BFD. Using BFD
consists of making references though the BFD and to data in the BFD.
Here is the structure that defines the type bfd. It
contains the major data about the file and pointers
to the rest of the data.
struct _bfd
{
/* The filename the application opened the BFD with. */
CONST char *filename;
/* A pointer to the target jump table. */
const struct bfd_target *xvec;
/* To avoid dragging too many header files into every file that
includes `bfd.h', IOSTREAM has been declared as a "char
*", and MTIME as a "long". Their correct types, to which they
are cast when used, are "FILE *" and "time_t". The iostream
is the result of an fopen on the filename. However, if the
BFD_IN_MEMORY flag is set, then iostream is actually a pointer
to a bfd_in_memory struct. */
PTR iostream;
/* Is the file descriptor being cached? That is, can it be closed as
needed, and re-opened when accessed later? */
boolean cacheable;
/* Marks whether there was a default target specified when the
BFD was opened. This is used to select which matching algorithm
to use to choose the back end. */
boolean target_defaulted;
/* The caching routines use these to maintain a
least-recently-used list of BFDs */
struct _bfd *lru_prev, *lru_next;
/* When a file is closed by the caching routines, BFD retains
state information on the file here: */
file_ptr where;
/* and here: (``once'' means at least once) */
boolean opened_once;
/* Set if we have a locally maintained mtime value, rather than
getting it from the file each time: */
boolean mtime_set;
/* File modified time, if mtime_set is true: */
long mtime;
/* Reserved for an unimplemented file locking extension.*/
int ifd;
/* The format which belongs to the BFD. (object, core, etc.) */
bfd_format format;
/* The direction the BFD was opened with*/
enum bfd_direction {no_direction = 0,
read_direction = 1,
write_direction = 2,
both_direction = 3} direction;
/* Format_specific flags*/
flagword flags;
/* Currently my_archive is tested before adding origin to
anything. I believe that this can become always an add of
origin, with origin set to 0 for non archive files. */
file_ptr origin;
/* Remember when output has begun, to stop strange things
from happening. */
boolean output_has_begun;
/* Pointer to linked list of sections*/
struct sec *sections;
/* The number of sections */
unsigned int section_count;
/* Stuff only useful for object files:
The start address. */
bfd_vma start_address;
/* Used for input and output*/
unsigned int symcount;
/* Symbol table for output BFD (with symcount entries) */
struct symbol_cache_entry **outsymbols;
/* Pointer to structure which contains architecture information*/
const struct bfd_arch_info *arch_info;
/* Stuff only useful for archives:*/
PTR arelt_data;
struct _bfd *my_archive; /* The containing archive BFD. */
struct _bfd *next; /* The next BFD in the archive. */
struct _bfd *archive_head; /* The first BFD in the archive. */
boolean has_armap;
/* A chain of BFD structures involved in a link. */
struct _bfd *link_next;
/* A field used by _bfd_generic_link_add_archive_symbols. This will
be used only for archive elements. */
int archive_pass;
/* Used by the back end to hold private data. */
union
{
struct aout_data_struct *aout_data;
struct artdata *aout_ar_data;
struct _oasys_data *oasys_obj_data;
struct _oasys_ar_data *oasys_ar_data;
struct coff_tdata *coff_obj_data;
struct pe_tdata *pe_obj_data;
struct xcoff_tdata *xcoff_obj_data;
struct ecoff_tdata *ecoff_obj_data;
struct ieee_data_struct *ieee_data;
struct ieee_ar_data_struct *ieee_ar_data;
struct srec_data_struct *srec_data;
struct ihex_data_struct *ihex_data;
struct tekhex_data_struct *tekhex_data;
struct elf_obj_tdata *elf_obj_data;
struct nlm_obj_tdata *nlm_obj_data;
struct bout_data_struct *bout_data;
struct sun_core_struct *sun_core_data;
struct trad_core_struct *trad_core_data;
struct som_data_struct *som_data;
struct hpux_core_struct *hpux_core_data;
struct hppabsd_core_struct *hppabsd_core_data;
struct sgi_core_struct *sgi_core_data;
struct lynx_core_struct *lynx_core_data;
struct osf_core_struct *osf_core_data;
struct cisco_core_struct *cisco_core_data;
struct versados_data_struct *versados_data;
struct netbsd_core_struct *netbsd_core_data;
PTR any;
} tdata;
/* Used by the application to hold private data*/
PTR usrdata;
/* Where all the allocated stuff under this BFD goes. This is a
struct objalloc *, but we use PTR to avoid requiring the inclusion of
objalloc.h. */
PTR memory;
};
Most BFD functions return nonzero on success (check their
individual documentation for precise semantics). On an error,
they call bfd_set_error to set an error condition that callers
can check by calling bfd_get_error.
If that returns bfd_error_system_call, then check
errno.
The easiest way to report a BFD error to the user is to
use bfd_perror.
bfd_error_type
The values returned by bfd_get_error are defined by the
enumerated type bfd_error_type.
typedef enum bfd_error
{
bfd_error_no_error = 0,
bfd_error_system_call,
bfd_error_invalid_target,
bfd_error_wrong_format,
bfd_error_invalid_operation,
bfd_error_no_memory,
bfd_error_no_symbols,
bfd_error_no_armap,
bfd_error_no_more_archived_files,
bfd_error_malformed_archive,
bfd_error_file_not_recognized,
bfd_error_file_ambiguously_recognized,
bfd_error_no_contents,
bfd_error_nonrepresentable_section,
bfd_error_no_debug_section,
bfd_error_bad_value,
bfd_error_file_truncated,
bfd_error_file_too_big,
bfd_error_invalid_error_code
} bfd_error_type;
bfd_get_errorSynopsis
bfd_error_type bfd_get_error (void);
Description
Return the current BFD error condition.
bfd_set_errorSynopsis
void bfd_set_error (bfd_error_type error_tag);
Description
Set the BFD error condition to be error_tag.
bfd_errmsgSynopsis
CONST char *bfd_errmsg (bfd_error_type error_tag);
Description
Return a string describing the error error_tag, or
the system error if error_tag is bfd_error_system_call.
bfd_perrorSynopsis
void bfd_perror (CONST char *message);
Description
Print to the standard error stream a string describing the
last BFD error that occurred, or the last system error if
the last BFD error was a system call failure. If message
is non-NULL and non-empty, the error string printed is preceded
by message, a colon, and a space. It is followed by a newline.
Some BFD functions want to print messages describing the problem. They call a BFD error handler function. This function may be overriden by the program.
The BFD error handler acts like printf.
typedef void (*bfd_error_handler_type) PARAMS ((const char *, ...));
bfd_set_error_handlerSynopsis
bfd_error_handler_type bfd_set_error_handler (bfd_error_handler_type);
Description
Set the BFD error handler function. Returns the previous
function.
bfd_set_error_program_nameSynopsis
void bfd_set_error_program_name (const char *);
Description
Set the program name to use when printing a BFD error. This
is printed before the error message followed by a colon and
space. The string must not be changed after it is passed to
this function.
bfd_get_error_handlerSynopsis
bfd_error_handler_type bfd_get_error_handler (void);
Description
Return the BFD error handler function.
bfd_get_reloc_upper_boundSynopsis
long bfd_get_reloc_upper_bound(bfd *abfd, asection *sect);
Description
Return the number of bytes required to store the
relocation information associated with section sect
attached to bfd abfd. If an error occurs, return -1.
bfd_canonicalize_relocSynopsis
long bfd_canonicalize_reloc
(bfd *abfd,
asection *sec,
arelent **loc,
asymbol **syms);
Description
Call the back end associated with the open BFD
abfd and translate the external form of the relocation
information attached to sec into the internal canonical
form. Place the table into memory at loc, which has
been preallocated, usually by a call to
bfd_get_reloc_upper_bound. Returns the number of relocs, or
-1 on error.
The syms table is also needed for horrible internal magic reasons.
bfd_set_relocSynopsis
void bfd_set_reloc (bfd *abfd, asection *sec, arelent **rel, unsigned int count)
Description
Set the relocation pointer and count within
section sec to the values rel and count.
The argument abfd is ignored.
bfd_set_file_flagsSynopsis
boolean bfd_set_file_flags(bfd *abfd, flagword flags);
Description
Set the flag word in the BFD abfd to the value flags.
Possible errors are:
bfd_error_wrong_format - The target bfd was not of object format.
bfd_error_invalid_operation - The target bfd was open for reading.
bfd_error_invalid_operation -
The flag word contained a bit which was not applicable to the
type of file. E.g., an attempt was made to set the D_PAGED bit
on a BFD format which does not support demand paging.
bfd_set_start_addressSynopsis
boolean bfd_set_start_address(bfd *abfd, bfd_vma vma);
Description
Make vma the entry point of output BFD abfd.
Returns
Returns true on success, false otherwise.
bfd_get_mtimeSynopsis
long bfd_get_mtime(bfd *abfd);
Description
Return the file modification time (as read from the file system, or
from the archive header for archive members).
bfd_get_sizeSynopsis
long bfd_get_size(bfd *abfd);
Description
Return the file size (as read from file system) for the file
associated with BFD abfd.
The initial motivation for, and use of, this routine is not so we can get the exact size of the object the BFD applies to, since that might not be generally possible (archive members for example). It would be ideal if someone could eventually modify it so that such results were guaranteed.
Instead, we want to ask questions like "is this NNN byte sized
object I'm about to try read from file offset YYY reasonable?"
As as example of where we might do this, some object formats
use string tables for which the first sizeof(long) bytes of the
table contain the size of the table itself, including the size bytes.
If an application tries to read what it thinks is one of these
string tables, without some way to validate the size, and for
some reason the size is wrong (byte swapping error, wrong location
for the string table, etc.), the only clue is likely to be a read
error when it tries to read the table, or a "virtual memory
exhausted" error when it tries to allocate 15 bazillon bytes
of space for the 15 bazillon byte table it is about to read.
This function at least allows us to answer the quesion, "is the
size reasonable?".
bfd_get_gp_sizeSynopsis
int bfd_get_gp_size(bfd *abfd);
Description
Return the maximum size of objects to be optimized using the GP
register under MIPS ECOFF. This is typically set by the -G
argument to the compiler, assembler or linker.
bfd_set_gp_sizeSynopsis
void bfd_set_gp_size(bfd *abfd, int i);
Description
Set the maximum size of objects to be optimized using the GP
register under ECOFF or MIPS ELF. This is typically set by
the -G argument to the compiler, assembler or linker.
bfd_scan_vmaSynopsis
bfd_vma bfd_scan_vma(CONST char *string, CONST char **end, int base);
Description
Convert, like strtoul, a numerical expression
string into a bfd_vma integer, and return that integer.
(Though without as many bells and whistles as strtoul.)
The expression is assumed to be unsigned (i.e., positive).
If given a base, it is used as the base for conversion.
A base of 0 causes the function to interpret the string
in hex if a leading "0x" or "0X" is found, otherwise
in octal if a leading zero is found, otherwise in decimal.
Overflow is not detected.
bfd_copy_private_bfd_dataSynopsis
boolean bfd_copy_private_bfd_data(bfd *ibfd, bfd *obfd);
Description
Copy private BFD information from the BFD ibfd to the
the BFD obfd. Return true on success, false on error.
Possible error returns are:
bfd_error_no_memory -
Not enough memory exists to create private data for obfd.
#define bfd_copy_private_bfd_data(ibfd, obfd) \
BFD_SEND (obfd, _bfd_copy_private_bfd_data, \
(ibfd, obfd))
bfd_merge_private_bfd_dataSynopsis
boolean bfd_merge_private_bfd_data(bfd *ibfd, bfd *obfd);
Description
Merge private BFD information from the BFD ibfd to the
the output file BFD obfd when linking. Return true
on success, false on error. Possible error returns are:
bfd_error_no_memory -
Not enough memory exists to create private data for obfd.
#define bfd_merge_private_bfd_data(ibfd, obfd) \
BFD_SEND (obfd, _bfd_merge_private_bfd_data, \
(ibfd, obfd))
bfd_set_private_flagsSynopsis
boolean bfd_set_private_flags(bfd *abfd, flagword flags);
Description
Set private BFD flag information in the BFD abfd.
Return true on success, false on error. Possible error
returns are:
bfd_error_no_memory -
Not enough memory exists to create private data for obfd.
#define bfd_set_private_flags(abfd, flags) \
BFD_SEND (abfd, _bfd_set_private_flags, \
(abfd, flags))
stuff
Description
Stuff which should be documented:
#define bfd_sizeof_headers(abfd, reloc) \
BFD_SEND (abfd, _bfd_sizeof_headers, (abfd, reloc))
#define bfd_find_nearest_line(abfd, sec, syms, off, file, func, line) \
BFD_SEND (abfd, _bfd_find_nearest_line, (abfd, sec, syms, off, file, func, line))
/* Do these three do anything useful at all, for any back end? */
#define bfd_debug_info_start(abfd) \
BFD_SEND (abfd, _bfd_debug_info_start, (abfd))
#define bfd_debug_info_end(abfd) \
BFD_SEND (abfd, _bfd_debug_info_end, (abfd))
#define bfd_debug_info_accumulate(abfd, section) \
BFD_SEND (abfd, _bfd_debug_info_accumulate, (abfd, section))
#define bfd_stat_arch_elt(abfd, stat) \
BFD_SEND (abfd, _bfd_stat_arch_elt,(abfd, stat))
#define bfd_update_armap_timestamp(abfd) \
BFD_SEND (abfd, _bfd_update_armap_timestamp, (abfd))
#define bfd_set_arch_mach(abfd, arch, mach)\
BFD_SEND ( abfd, _bfd_set_arch_mach, (abfd, arch, mach))
#define bfd_relax_section(abfd, section, link_info, again) \
BFD_SEND (abfd, _bfd_relax_section, (abfd, section, link_info, again))
#define bfd_link_hash_table_create(abfd) \
BFD_SEND (abfd, _bfd_link_hash_table_create, (abfd))
#define bfd_link_add_symbols(abfd, info) \
BFD_SEND (abfd, _bfd_link_add_symbols, (abfd, info))
#define bfd_final_link(abfd, info) \
BFD_SEND (abfd, _bfd_final_link, (abfd, info))
#define bfd_free_cached_info(abfd) \
BFD_SEND (abfd, _bfd_free_cached_info, (abfd))
#define bfd_get_dynamic_symtab_upper_bound(abfd) \
BFD_SEND (abfd, _bfd_get_dynamic_symtab_upper_bound, (abfd))
#define bfd_print_private_bfd_data(abfd, file)\
BFD_SEND (abfd, _bfd_print_private_bfd_data, (abfd, file))
#define bfd_canonicalize_dynamic_symtab(abfd, asymbols) \
BFD_SEND (abfd, _bfd_canonicalize_dynamic_symtab, (abfd, asymbols))
#define bfd_get_dynamic_reloc_upper_bound(abfd) \
BFD_SEND (abfd, _bfd_get_dynamic_reloc_upper_bound, (abfd))
#define bfd_canonicalize_dynamic_reloc(abfd, arels, asyms) \
BFD_SEND (abfd, _bfd_canonicalize_dynamic_reloc, (abfd, arels, asyms))
extern bfd_byte *bfd_get_relocated_section_contents
PARAMS ((bfd *, struct bfd_link_info *,
struct bfd_link_order *, bfd_byte *,
boolean, asymbol **));
BFD keeps all of its internal structures in obstacks. There is one obstack per open BFD file, into which the current state is stored. When a BFD is closed, the obstack is deleted, and so everything which has been allocated by BFD for the closing file is thrown away.
BFD does not free anything created by an application, but pointers into
bfd structures become invalid on a bfd_close; for example,
after a bfd_close the vector passed to
bfd_canonicalize_symtab is still around, since it has been
allocated by the application, but the data that it pointed to are
lost.
The general rule is to not close a BFD until all operations dependent
upon data from the BFD have been completed, or all the data from within
the file has been copied. To help with the management of memory, there
is a function (bfd_alloc_size) which returns the number of bytes
in obstacks associated with the supplied BFD. This could be used to
select the greediest open BFD, close it to reclaim the memory, perform
some operation and reopen the BFD again, to get a fresh copy of the data
structures.
These are the functions that handle initializing a BFD.
bfd_initSynopsis
void bfd_init(void);
Description
This routine must be called before any other BFD function to
initialize magical internal data structures.
The raw data contained within a BFD is maintained through the section abstraction. A single BFD may have any number of sections. It keeps hold of them by pointing to the first; each one points to the next in the list.
Sections are supported in BFD in section.c.
When a BFD is opened for reading, the section structures are created and attached to the BFD.
Each section has a name which describes the section in the
outside world--for example, a.out would contain at least
three sections, called .text, .data and .bss.
Names need not be unique; for example a COFF file may have several
sections named .data.
Sometimes a BFD will contain more than the "natural" number of
sections. A back end may attach other sections containing
constructor data, or an application may add a section (using
bfd_make_section) to the sections attached to an already open
BFD. For example, the linker creates an extra section
COMMON for each input file's BFD to hold information about
common storage.
The raw data is not necessarily read in when
the section descriptor is created. Some targets may leave the
data in place until a bfd_get_section_contents call is
made. Other back ends may read in all the data at once. For
example, an S-record file has to be read once to determine the
size of the data. An IEEE-695 file doesn't contain raw data in
sections, but data and relocation expressions intermixed, so
the data area has to be parsed to get out the data and
relocations.
To write a new object style BFD, the various sections to be
written have to be created. They are attached to the BFD in
the same way as input sections; data is written to the
sections using bfd_set_section_contents.
Any program that creates or combines sections (e.g., the assembler
and linker) must use the asection fields output_section and
output_offset to indicate the file sections to which each
section must be written. (If the section is being created from
scratch, output_section should probably point to the section
itself and output_offset should probably be zero.)
The data to be written comes from input sections attached
(via output_section pointers) to
the output sections. The output section structure can be
considered a filter for the input section: the output section
determines the vma of the output data and the name, but the
input section determines the offset into the output section of
the data to be written.
E.g., to create a section "O", starting at 0x100, 0x123 long,
containing two subsections, "A" at offset 0x0 (i.e., at vma
0x100) and "B" at offset 0x20 (i.e., at vma 0x120) the asection
structures would look like:
section name "A"
output_offset 0x00
size 0x20
output_section -----------> section name "O"
| vma 0x100
section name "B" | size 0x123
output_offset 0x20 |
size 0x103 |
output_section --------|
The data within a section is stored in a link_order.
These are much like the fixups in gas. The link_order
abstraction allows a section to grow and shrink within itself.
A link_order knows how big it is, and which is the next link_order and where the raw data for it is; it also points to a list of relocations which apply to it.
The link_order is used by the linker to perform relaxing on final code. The compiler creates code which is as big as necessary to make it work without relaxing, and the user can select whether to relax. Sometimes relaxing takes a lot of time. The linker runs around the relocations to see if any are attached to data which can be shrunk, if so it does it on a link_order by link_order basis.
Here is the section structure:
typedef struct sec
{
/* The name of the section; the name isn't a copy, the pointer is
the same as that passed to bfd_make_section. */
CONST char *name;
/* Which section is it; 0..nth. */
int index;
/* The next section in the list belonging to the BFD, or NULL. */
struct sec *next;
/* The field flags contains attributes of the section. Some
flags are read in from the object file, and some are
synthesized from other information. */
flagword flags;
#define SEC_NO_FLAGS 0x000
/* Tells the OS to allocate space for this section when loading.
This is clear for a section containing debug information
only. */
#define SEC_ALLOC 0x001
/* Tells the OS to load the section from the file when loading.
This is clear for a .bss section. */
#define SEC_LOAD 0x002
/* The section contains data still to be relocated, so there is
some relocation information too. */
#define SEC_RELOC 0x004
#if 0 /* Obsolete ? */
#define SEC_BALIGN 0x008
#endif
/* A signal to the OS that the section contains read only
data. */
#define SEC_READONLY 0x010
/* The section contains code only. */
#define SEC_CODE 0x020
/* The section contains data only. */
#define SEC_DATA 0x040
/* The section will reside in ROM. */
#define SEC_ROM 0x080
/* The section contains constructor information. This section
type is used by the linker to create lists of constructors and
destructors used by g++. When a back end sees a symbol
which should be used in a constructor list, it creates a new
section for the type of name (e.g., __CTOR_LIST__), attaches
the symbol to it, and builds a relocation. To build the lists
of constructors, all the linker has to do is catenate all the
sections called __CTOR_LIST__ and relocate the data
contained within - exactly the operations it would peform on
standard data. */
#define SEC_CONSTRUCTOR 0x100
/* The section is a constuctor, and should be placed at the
end of the text, data, or bss section(?). */
#define SEC_CONSTRUCTOR_TEXT 0x1100
#define SEC_CONSTRUCTOR_DATA 0x2100
#define SEC_CONSTRUCTOR_BSS 0x3100
/* The section has contents - a data section could be
SEC_ALLOC | SEC_HAS_CONTENTS; a debug section could be
SEC_HAS_CONTENTS */
#define SEC_HAS_CONTENTS 0x200
/* An instruction to the linker to not output the section
even if it has information which would normally be written. */
#define SEC_NEVER_LOAD 0x400
/* The section is a COFF shared library section. This flag is
only for the linker. If this type of section appears in
the input file, the linker must copy it to the output file
without changing the vma or size. FIXME: Although this
was originally intended to be general, it really is COFF
specific (and the flag was renamed to indicate this). It
might be cleaner to have some more general mechanism to
allow the back end to control what the linker does with
sections. */
#define SEC_COFF_SHARED_LIBRARY 0x800
/* The section contains common symbols (symbols may be defined
multiple times, the value of a symbol is the amount of
space it requires, and the largest symbol value is the one
used). Most targets have exactly one of these (which we
translate to bfd_com_section_ptr), but ECOFF has two. */
#define SEC_IS_COMMON 0x8000
/* The section contains only debugging information. For
example, this is set for ELF .debug and .stab sections.
strip tests this flag to see if a section can be
discarded. */
#define SEC_DEBUGGING 0x10000
/* The contents of this section are held in memory pointed to
by the contents field. This is checked by
bfd_get_section_contents, and the data is retrieved from
memory if appropriate. */
#define SEC_IN_MEMORY 0x20000
/* The contents of this section are to be excluded by the
linker for executable and shared objects unless those
objects are to be further relocated. */
#define SEC_EXCLUDE 0x40000
/* The contents of this section are to be sorted by the
based on the address specified in the associated symbol
table. */
#define SEC_SORT_ENTRIES 0x80000
/* When linking, duplicate sections of the same name should be
discarded, rather than being combined into a single section as
is usually done. This is similar to how common symbols are
handled. See SEC_LINK_DUPLICATES below. */
#define SEC_LINK_ONCE 0x100000
/* If SEC_LINK_ONCE is set, this bitfield describes how the linker
should handle duplicate sections. */
#define SEC_LINK_DUPLICATES 0x600000
/* This value for SEC_LINK_DUPLICATES means that duplicate
sections with the same name should simply be discarded. */
#define SEC_LINK_DUPLICATES_DISCARD 0x0
/* This value for SEC_LINK_DUPLICATES means that the linker
should warn if there are any duplicate sections, although
it should still only link one copy. */
#define SEC_LINK_DUPLICATES_ONE_ONLY 0x200000
/* This value for SEC_LINK_DUPLICATES means that the linker
should warn if any duplicate sections are a different size. */
#define SEC_LINK_DUPLICATES_SAME_SIZE 0x400000
/* This value for SEC_LINK_DUPLICATES means that the linker
should warn if any duplicate sections contain different
contents. */
#define SEC_LINK_DUPLICATES_SAME_CONTENTS 0x600000
/* This section was created by the linker as part of dynamic
relocation or other arcane processing. It is skipped when
going through the first-pass output, trusting that someone
else up the line will take care of it later. */
#define SEC_LINKER_CREATED 0x800000
/* End of section flags. */
/* Some internal packed boolean fields. */
/* See the vma field. */
unsigned int user_set_vma : 1;
/* Whether relocations have been processed. */
unsigned int reloc_done : 1;
/* A mark flag used by some of the linker backends. */
unsigned int linker_mark : 1;
/* End of internal packed boolean fields. */
/* The virtual memory address of the section - where it will be
at run time. The symbols are relocated against this. The
user_set_vma flag is maintained by bfd; if it's not set, the
backend can assign addresses (for example, in a.out, where
the default address for .data is dependent on the specific
target and various flags). */
bfd_vma vma;
/* The load address of the section - where it would be in a
rom image; really only used for writing section header
information. */
bfd_vma lma;
/* The size of the section in bytes, as it will be output.
contains a value even if the section has no contents (e.g., the
size of .bss). This will be filled in after relocation */
bfd_size_type _cooked_size;
/* The original size on disk of the section, in bytes. Normally this
value is the same as the size, but if some relaxing has
been done, then this value will be bigger. */
bfd_size_type _raw_size;
/* If this section is going to be output, then this value is the
offset into the output section of the first byte in the input
section. E.g., if this was going to start at the 100th byte in
the output section, this value would be 100. */
bfd_vma output_offset;
/* The output section through which to map on output. */
struct sec *output_section;
/* The alignment requirement of the section, as an exponent of 2 -
e.g., 3 aligns to 2^3 (or 8). */
unsigned int alignment_power;
/* If an input section, a pointer to a vector of relocation
records for the data in this section. */
struct reloc_cache_entry *relocation;
/* If an output section, a pointer to a vector of pointers to
relocation records for the data in this section. */
struct reloc_cache_entry **orelocation;
/* The number of relocation records in one of the above */
unsigned reloc_count;
/* Information below is back end specific - and not always used
or updated. */
/* File position of section data */
file_ptr filepos;
/* File position of relocation info */
file_ptr rel_filepos;
/* File position of line data */
file_ptr line_filepos;
/* Pointer to data for applications */
PTR userdata;
/* If the SEC_IN_MEMORY flag is set, this points to the actual
contents. */
unsigned char *contents;
/* Attached line number information */
alent *lineno;
/* Number of line number records */
unsigned int lineno_count;
/* When a section is being output, this value changes as more
linenumbers are written out */
file_ptr moving_line_filepos;
/* What the section number is in the target world */
int target_index;
PTR used_by_bfd;
/* If this is a constructor section then here is a list of the
relocations created to relocate items within it. */
struct relent_chain *constructor_chain;
/* The BFD which owns the section. */
bfd *owner;
/* A symbol which points at this section only */
struct symbol_cache_entry *symbol;
struct symbol_cache_entry **symbol_ptr_ptr;
struct bfd_link_order *link_order_head;
struct bfd_link_order *link_order_tail;
} asection ;
/* These sections are global, and are managed by BFD. The application
and target back end are not permitted to change the values in
these sections. New code should use the section_ptr macros rather
than referring directly to the const sections. The const sections
may eventually vanish. */
#define BFD_ABS_SECTION_NAME "*ABS*"
#define BFD_UND_SECTION_NAME "*UND*"
#define BFD_COM_SECTION_NAME "*COM*"
#define BFD_IND_SECTION_NAME "*IND*"
/* the absolute section */
extern const asection bfd_abs_section;
#define bfd_abs_section_ptr ((asection *) &bfd_abs_section)
#define bfd_is_abs_section(sec) ((sec) == bfd_abs_section_ptr)
/* Pointer to the undefined section */
extern const asection bfd_und_section;
#define bfd_und_section_ptr ((asection *) &bfd_und_section)
#define bfd_is_und_section(sec) ((sec) == bfd_und_section_ptr)
/* Pointer to the common section */
extern const asection bfd_com_section;
#define bfd_com_section_ptr ((asection *) &bfd_com_section)
/* Pointer to the indirect section */
extern const asection bfd_ind_section;
#define bfd_ind_section_ptr ((asection *) &bfd_ind_section)
#define bfd_is_ind_section(sec) ((sec) == bfd_ind_section_ptr)
extern const struct symbol_cache_entry * const bfd_abs_symbol;
extern const struct symbol_cache_entry * const bfd_com_symbol;
extern const struct symbol_cache_entry * const bfd_und_symbol;
extern const struct symbol_cache_entry * const bfd_ind_symbol;
#define bfd_get_section_size_before_reloc(section) \
(section->reloc_done ? (abort(),1): (section)->_raw_size)
#define bfd_get_section_size_after_reloc(section) \
((section->reloc_done) ? (section)->_cooked_size: (abort(),1))
These are the functions exported by the section handling part of BFD.
bfd_get_section_by_nameSynopsis
asection *bfd_get_section_by_name(bfd *abfd, CONST char *name);
Description
Run through abfd and return the one of the
asections whose name matches name, otherwise NULL.
See section Sections, for more information.
This should only be used in special cases; the normal way to process
all sections of a given name is to use bfd_map_over_sections and
strcmp on the name (or better yet, base it on the section flags
or something else) for each section.
bfd_make_section_old_waySynopsis
asection *bfd_make_section_old_way(bfd *abfd, CONST char *name);
Description
Create a new empty section called name
and attach it to the end of the chain of sections for the
BFD abfd. An attempt to create a section with a name which
is already in use returns its pointer without changing the
section chain.
It has the funny name since this is the way it used to be before it was rewritten....
Possible errors are:
bfd_error_invalid_operation -
If output has already started for this BFD.
bfd_error_no_memory -
If memory allocation fails.
bfd_make_section_anywaySynopsis
asection *bfd_make_section_anyway(bfd *abfd, CONST char *name);
Description
Create a new empty section called name and attach it to the end of
the chain of sections for abfd. Create a new section even if there
is already a section with that name.
Return NULL and set bfd_error on error; possible errors are:
bfd_error_invalid_operation - If output has already started for abfd.
bfd_error_no_memory - If memory allocation fails.
bfd_make_sectionSynopsis
asection *bfd_make_section(bfd *, CONST char *name);
Description
Like bfd_make_section_anyway, but return NULL (without calling
bfd_set_error ()) without changing the section chain if there is already a
section named name. If there is an error, return NULL and set
bfd_error.
bfd_set_section_flagsSynopsis
boolean bfd_set_section_flags(bfd *abfd, asection *sec, flagword flags);
Description
Set the attributes of the section sec in the BFD
abfd to the value flags. Return true on success,
false on error. Possible error returns are:
bfd_error_invalid_operation -
The section cannot have one or more of the attributes
requested. For example, a .bss section in a.out may not
have the SEC_HAS_CONTENTS field set.
bfd_map_over_sectionsSynopsis
void bfd_map_over_sections(bfd *abfd,
void (*func)(bfd *abfd,
asection *sect,
PTR obj),
PTR obj);
Description
Call the provided function func for each section
attached to the BFD abfd, passing obj as an
argument. The function will be called as if by
func(abfd, the_section, obj);
This is the prefered method for iterating over sections; an alternative would be to use a loop:
section *p;
for (p = abfd->sections; p != NULL; p = p->next)
func(abfd, p, ...)
bfd_set_section_sizeSynopsis
boolean bfd_set_section_size(bfd *abfd, asection *sec, bfd_size_type val);
Description
Set sec to the size val. If the operation is
ok, then true is returned, else false.
Possible error returns:
bfd_error_invalid_operation -
Writing has started to the BFD, so setting the size is invalid.
bfd_set_section_contentsSynopsis
boolean bfd_set_section_contents
(bfd *abfd,
asection *section,
PTR data,
file_ptr offset,
bfd_size_type count);
Description
Sets the contents of the section section in BFD
abfd to the data starting in memory at data. The
data is written to the output section starting at offset
offset for count bytes.
Normally true is returned, else false. Possible error
returns are:
bfd_error_no_contents -
The output section does not have the SEC_HAS_CONTENTS
attribute, so nothing can be written to it.
This routine is front end to the back end function
_bfd_set_section_contents.
bfd_get_section_contentsSynopsis
boolean bfd_get_section_contents
(bfd *abfd, asection *section, PTR location,
file_ptr offset, bfd_size_type count);
Description
Read data from section in BFD abfd
into memory starting at location. The data is read at an
offset of offset from the start of the input section,
and is read for count bytes.
If the contents of a constructor with the SEC_CONSTRUCTOR
flag set are requested or if the section does not have the
SEC_HAS_CONTENTS flag set, then the location is filled
with zeroes. If no errors occur, true is returned, else
false.
bfd_copy_private_section_dataSynopsis
boolean bfd_copy_private_section_data(bfd *ibfd, asection *isec, bfd *obfd, asection *osec);
Description
Copy private section information from isec in the BFD
ibfd to the section osec in the BFD obfd.
Return true on success, false on error. Possible error
returns are:
bfd_error_no_memory -
Not enough memory exists to create private data for osec.
#define bfd_copy_private_section_data(ibfd, isection, obfd, osection) \
BFD_SEND (obfd, _bfd_copy_private_section_data, \
(ibfd, isection, obfd, osection))
BFD tries to maintain as much symbol information as it can when
it moves information from file to file. BFD passes information
to applications though the asymbol structure. When the
application requests the symbol table, BFD reads the table in
the native form and translates parts of it into the internal
format. To maintain more than the information passed to
applications, some targets keep some information "behind the
scenes" in a structure only the particular back end knows
about. For example, the coff back end keeps the original
symbol table structure as well as the canonical structure when
a BFD is read in. On output, the coff back end can reconstruct
the output symbol table so that no information is lost, even
information unique to coff which BFD doesn't know or
understand. If a coff symbol table were read, but were written
through an a.out back end, all the coff specific information
would be lost. The symbol table of a BFD
is not necessarily read in until a canonicalize request is
made. Then the BFD back end fills in a table provided by the
application with pointers to the canonical information. To
output symbols, the application provides BFD with a table of
pointers to pointers to asymbols. This allows applications
like the linker to output a symbol as it was read, since the "behind
the scenes" information will be still available.
There are two stages to reading a symbol table from a BFD: allocating storage, and the actual reading process. This is an excerpt from an application which reads the symbol table:
long storage_needed;
asymbol **symbol_table;
long number_of_symbols;
long i;
storage_needed = bfd_get_symtab_upper_bound (abfd);
if (storage_needed < 0)
FAIL
if (storage_needed == 0) {
return ;
}
symbol_table = (asymbol **) xmalloc (storage_needed);
...
number_of_symbols =
bfd_canonicalize_symtab (abfd, symbol_table);
if (number_of_symbols < 0)
FAIL
for (i = 0; i < number_of_symbols; i++) {
process_symbol (symbol_table[i]);
}
All storage for the symbols themselves is in an objalloc connected to the BFD; it is freed when the BFD is closed.
Writing of a symbol table is automatic when a BFD open for
writing is closed. The application attaches a vector of
pointers to pointers to symbols to the BFD being written, and
fills in the symbol count. The close and cleanup code reads
through the table provided and performs all the necessary
operations. The BFD output code must always be provided with an
"owned" symbol: one which has come from another BFD, or one
which has been created using bfd_make_empty_symbol. Here is an
example showing the creation of a symbol table with only one element:
#include "bfd.h"
main()
{
bfd *abfd;
asymbol *ptrs[2];
asymbol *new;
abfd = bfd_openw("foo","a.out-sunos-big");
bfd_set_format(abfd, bfd_object);
new = bfd_make_empty_symbol(abfd);
new->name = "dummy_symbol";
new->section = bfd_make_section_old_way(abfd, ".text");
new->flags = BSF_GLOBAL;
new->value = 0x12345;
ptrs[0] = new;
ptrs[1] = (asymbol *)0;
bfd_set_symtab(abfd, ptrs, 1);
bfd_close(abfd);
}
./makesym
nm foo
00012345 A dummy_symbol
Many formats cannot represent arbitary symbol information; for
instance, the a.out object format does not allow an
arbitary number of sections. A symbol pointing to a section
which is not one of .text, .data or .bss cannot
be described.
Mini symbols provide read-only access to the symbol table. They use less memory space, but require more time to access. They can be useful for tools like nm or objdump, which may have to handle symbol tables of extremely large executables.
The bfd_read_minisymbols function will read the symbols
into memory in an internal form. It will return a void *
pointer to a block of memory, a symbol count, and the size of
each symbol. The pointer is allocated using malloc, and
should be freed by the caller when it is no longer needed.
The function bfd_minisymbol_to_symbol will take a pointer
to a minisymbol, and a pointer to a structure returned by
bfd_make_empty_symbol, and return a asymbol structure.
The return value may or may not be the same as the value from
bfd_make_empty_symbol which was passed in.
An asymbol has the form:
typedef struct symbol_cache_entry
{
/* A pointer to the BFD which owns the symbol. This information
is necessary so that a back end can work out what additional
information (invisible to the application writer) is carried
with the symbol.
This field is *almost* redundant, since you can use section->owner
instead, except that some symbols point to the global sections
bfd_{abs,com,und}_section. This could be fixed by making
these globals be per-bfd (or per-target-flavor). FIXME. */
struct _bfd *the_bfd; /* Use bfd_asymbol_bfd(sym) to access this field. */
/* The text of the symbol. The name is left alone, and not copied; the
application may not alter it. */
CONST char *name;
/* The value of the symbol. This really should be a union of a
numeric value with a pointer, since some flags indicate that
a pointer to another symbol is stored here. */
symvalue value;
/* Attributes of a symbol: */
#define BSF_NO_FLAGS 0x00
/* The symbol has local scope; static in C. The value
is the offset into the section of the data. */
#define BSF_LOCAL 0x01
/* The symbol has global scope; initialized data in C. The
value is the offset into the section of the data. */
#define BSF_GLOBAL 0x02
/* The symbol has global scope and is exported. The value is
the offset into the section of the data. */
#define BSF_EXPORT BSF_GLOBAL /* no real difference */
/* A normal C symbol would be one of:
BSF_LOCAL, BSF_FORT_COMM, BSF_UNDEFINED or
BSF_GLOBAL */
/* The symbol is a debugging record. The value has an arbitary
meaning. */
#define BSF_DEBUGGING 0x08
/* The symbol denotes a function entry point. Used in ELF,
perhaps others someday. */
#define BSF_FUNCTION 0x10
/* Used by the linker. */
#define BSF_KEEP 0x20
#define BSF_KEEP_G 0x40
/* A weak global symbol, overridable without warnings by
a regular global symbol of the same name. */
#define BSF_WEAK 0x80
/* This symbol was created to point to a section, e.g. ELF's
STT_SECTION symbols. */
#define BSF_SECTION_SYM 0x100
/* The symbol used to be a common symbol, but now it is
allocated. */
#define BSF_OLD_COMMON 0x200
/* The default value for common data. */
#define BFD_FORT_COMM_DEFAULT_VALUE 0
/* In some files the type of a symbol sometimes alters its
location in an output file - ie in coff a ISFCN symbol
which is also C_EXT symbol appears where it was
declared and not at the end of a section. This bit is set
by the target BFD part to convey this information. */
#define BSF_NOT_AT_END 0x400
/* Signal that the symbol is the label of constructor section. */
#define BSF_CONSTRUCTOR 0x800
/* Signal that the symbol is a warning symbol. The name is a
warning. The name of the next symbol is the one to warn about;
if a reference is made to a symbol with the same name as the next
symbol, a warning is issued by the linker. */
#define BSF_WARNING 0x1000
/* Signal that the symbol is indirect. This symbol is an indirect
pointer to the symbol with the same name as the next symbol. */
#define BSF_INDIRECT 0x2000
/* BSF_FILE marks symbols that contain a file name. This is used
for ELF STT_FILE symbols. */
#define BSF_FILE 0x4000
/* Symbol is from dynamic linking information. */
#define BSF_DYNAMIC 0x8000
/* The symbol denotes a data object. Used in ELF, and perhaps
others someday. */
#define BSF_OBJECT 0x10000
flagword flags;
/* A pointer to the section to which this symbol is
relative. This will always be non NULL, there are special
sections for undefined and absolute symbols. */
struct sec *section;
/* Back end special data. */
union
{
PTR p;
bfd_vma i;
} udata;
} asymbol;
bfd_get_symtab_upper_bound
Description
Return the number of bytes required to store a vector of pointers
to asymbols for all the symbols in the BFD abfd,
including a terminal NULL pointer. If there are no symbols in
the BFD, then return 0. If an error occurs, return -1.
#define bfd_get_symtab_upper_bound(abfd) \
BFD_SEND (abfd, _bfd_get_symtab_upper_bound, (abfd))
bfd_is_local_labelSynopsis
boolean bfd_is_local_label(bfd *abfd, asymbol *sym);
Description
Return true if the given symbol sym in the BFD abfd is
a compiler generated local label, else return false.
bfd_is_local_label_nameSynopsis
boolean bfd_is_local_label_name(bfd *abfd, const char *name);
Description
Return true if a symbol with the name name in the BFD
abfd is a compiler generated local label, else return
false. This just checks whether the name has the form of a
local label.
#define bfd_is_local_label_name(abfd, name) \
BFD_SEND (abfd, _bfd_is_local_label_name, (abfd, name))
bfd_canonicalize_symtab
Description
Read the symbols from the BFD abfd, and fills in
the vector location with pointers to the symbols and
a trailing NULL.
Return the actual number of symbol pointers, not
including the NULL.
#define bfd_canonicalize_symtab(abfd, location) \
BFD_SEND (abfd, _bfd_canonicalize_symtab,\
(abfd, location))
bfd_set_symtabSynopsis
boolean bfd_set_symtab (bfd *abfd, asymbol **location, unsigned int count);
Description
Arrange that when the output BFD abfd is closed,
the table location of count pointers to symbols
will be written.
bfd_print_symbol_vandfSynopsis
void bfd_print_symbol_vandf(PTR file, asymbol *symbol);
Description
Print the value and flags of the symbol supplied to the
stream file.
bfd_make_empty_symbol
Description
Create a new asymbol structure for the BFD abfd
and return a pointer to it.
This routine is necessary because each back end has private
information surrounding the asymbol. Building your own
asymbol and pointing to it will not create the private
information, and will cause problems later on.
#define bfd_make_empty_symbol(abfd) \
BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
bfd_make_debug_symbol
Description
Create a new asymbol structure for the BFD abfd,
to be used as a debugging symbol. Further details of its use have
yet to be worked out.
#define bfd_make_debug_symbol(abfd,ptr,size) \
BFD_SEND (abfd, _bfd_make_debug_symbol, (abfd, ptr, size))
bfd_decode_symclass
Description
Return a character corresponding to the symbol
class of symbol, or '?' for an unknown class.
Synopsis
int bfd_decode_symclass(asymbol *symbol);
bfd_symbol_info
Description
Fill in the basic info about symbol that nm needs.
Additional info may be added by the back-ends after
calling this function.
Synopsis
void bfd_symbol_info(asymbol *symbol, symbol_info *ret);
bfd_copy_private_symbol_dataSynopsis
boolean bfd_copy_private_symbol_data(bfd *ibfd, asymbol *isym, bfd *obfd, asymbol *osym);
Description
Copy private symbol information from isym in the BFD
ibfd to the symbol osym in the BFD obfd.
Return true on success, false on error. Possible error
returns are:
bfd_error_no_memory -
Not enough memory exists to create private data for osec.
#define bfd_copy_private_symbol_data(ibfd, isymbol, obfd, osymbol) \
BFD_SEND (obfd, _bfd_copy_private_symbol_data, \
(ibfd, isymbol, obfd, osymbol))
Description
An archive (or library) is just another BFD. It has a symbol
table, although there's not much a user program will do with it.
The big difference between an archive BFD and an ordinary BFD is that the archive doesn't have sections. Instead it has a chain of BFDs that are considered its contents. These BFDs can be manipulated like any other. The BFDs contained in an archive opened for reading will all be opened for reading. You may put either input or output BFDs into an archive opened for output; they will be handled correctly when the archive is closed.
Use bfd_openr_next_archived_file to step through
the contents of an archive opened for input. You don't
have to read the entire archive if you don't want
to! Read it until you find what you want.
Archive contents of output BFDs are chained through the
next pointer in a BFD. The first one is findable through
the archive_head slot of the archive. Set it with
bfd_set_archive_head (q.v.). A given BFD may be in only one
open output archive at a time.
As expected, the BFD archive code is more general than the archive code of any given environment. BFD archives may contain files of different formats (e.g., a.out and coff) and even different architectures. You may even place archives recursively into archives!
This can cause unexpected confusion, since some archive formats are more expressive than others. For instance, Intel COFF archives can preserve long filenames; SunOS a.out archives cannot. If you move a file from the first to the second format and back again, the filename may be truncated. Likewise, different a.out environments have different conventions as to how they truncate filenames, whether they preserve directory names in filenames, etc. When interoperating with native tools, be sure your files are homogeneous.
Beware: most of these formats do not react well to the presence of spaces in filenames. We do the best we can, but can't always handle this case due to restrictions in the format of archives. Many Unix utilities are braindead in regards to spaces and such in filenames anyway, so this shouldn't be much of a restriction.
Archives are supported in BFD in archive.c.
bfd_get_next_mapentSynopsis
symindex bfd_get_next_mapent(bfd *abfd, symindex previous, carsym **sym);
Description
Step through archive abfd's symbol table (if it
has one). Successively update sym with the next symbol's
information, returning that symbol's (internal) index into the
symbol table.
Supply BFD_NO_MORE_SYMBOLS as the previous entry to get
the first one; returns BFD_NO_MORE_SYMBOLS when you've already
got the last one.
A carsym is a canonical archive symbol. The only
user-visible element is its name, a null-terminated string.
bfd_set_archive_headSynopsis
boolean bfd_set_archive_head(bfd *output, bfd *new_head);
Description
Set the head of the chain of
BFDs contained in the archive output to new_head.
bfd_openr_next_archived_fileSynopsis
bfd *bfd_openr_next_archived_file(bfd *archive, bfd *previous);
Description
Provided a BFD, archive, containing an archive and NULL, open
an input BFD on the first contained element and returns that.
Subsequent calls should pass
the archive and the previous return value to return a created
BFD to the next contained element. NULL is returned when there
are no more.
A format is a BFD concept of high level file contents type. The formats supported by BFD are:
bfd_object
The BFD may contain data, symbols, relocations and debug info.
bfd_archive
The BFD contains other BFDs and an optional index.
bfd_core
The BFD contains the result of an executable core dump.
bfd_check_formatSynopsis
boolean bfd_check_format(bfd *abfd, bfd_format format);
Description
Verify if the file attached to the BFD abfd is compatible
with the format format (i.e., one of bfd_object,
bfd_archive or bfd_core).
If the BFD has been set to a specific target before the
call, only the named target and format combination is
checked. If the target has not been set, or has been set to
default, then all the known target backends is
interrogated to determine a match. If the default target
matches, it is used. If not, exactly one target must recognize
the file, or an error results.
The function returns true on success, otherwise false
with one of the following error codes:
bfd_error_invalid_operation -
if format is not one of bfd_object, bfd_archive or
bfd_core.
bfd_error_system_call -
if an error occured during a read - even some file mismatches
can cause bfd_error_system_calls.
file_not_recognised -
none of the backends recognised the file format.
bfd_error_file_ambiguously_recognized -
more than one backend recognised the file format.
bfd_check_format_matchesSynopsis
boolean bfd_check_format_matches(bfd *abfd, bfd_format format, char ***matching);
Description
Like bfd_check_format, except when it returns false with
bfd_errno set to bfd_error_file_ambiguously_recognized. In that
case, if matching is not NULL, it will be filled in with
a NULL-terminated list of the names of the formats that matched,
allocated with malloc.
Then the user may choose a format and try again.
When done with the list that matching points to, the caller should free it.
bfd_set_formatSynopsis
boolean bfd_set_format(bfd *abfd, bfd_format format);
Description
This function sets the file format of the BFD abfd to the
format format. If the target set in the BFD does not
support the format requested, the format is invalid, or the BFD
is not open for writing, then an error occurs.
bfd_format_stringSynopsis
CONST char *bfd_format_string(bfd_format format);
Description
Return a pointer to a const string
invalid, object, archive, core, or unknown,
depending upon the value of format.
BFD maintains relocations in much the same way it maintains
symbols: they are left alone until required, then read in
en-mass and translated into an internal form. A common
routine bfd_perform_relocation acts upon the
canonical form to do the fixup.
Relocations are maintained on a per section basis, while symbols are maintained on a per BFD basis.
All that a back end has to do to fit the BFD interface is to create
a struct reloc_cache_entry for each relocation
in a particular section, and fill in the right bits of the structures.
This is the structure of a relocation entry:
typedef enum bfd_reloc_status
{
/* No errors detected */
bfd_reloc_ok,
/* The relocation was performed, but there was an overflow. */
bfd_reloc_overflow,
/* The address to relocate was not within the section supplied. */
bfd_reloc_outofrange,
/* Used by special functions */
bfd_reloc_continue,
/* Unsupported relocation size requested. */
bfd_reloc_notsupported,
/* Unused */
bfd_reloc_other,
/* The symbol to relocate against was undefined. */
bfd_reloc_undefined,
/* The relocation was performed, but may not be ok - presently
generated only when linking i960 coff files with i960 b.out
symbols. If this type is returned, the error_message argument
to bfd_perform_relocation will be set. */
bfd_reloc_dangerous
}
bfd_reloc_status_type;
typedef struct reloc_cache_entry
{
/* A pointer into the canonical table of pointers */
struct symbol_cache_entry **sym_ptr_ptr;
/* offset in section */
bfd_size_type address;
/* addend for relocation value */
bfd_vma addend;
/* Pointer to how to perform the required relocation */
reloc_howto_type *howto;
} arelent;
Description
Here is a description of each of the fields within an arelent:
sym_ptr_ptr
The symbol table pointer points to a pointer to the symbol
associated with the relocation request. It is
the pointer into the table returned by the back end's
get_symtab action. See section Symbols. The symbol is referenced
through a pointer to a pointer so that tools like the linker
can fix up all the symbols of the same name by modifying only
one pointer. The relocation routine looks in the symbol and
uses the base of the section the symbol is attached to and the
value of the symbol as the initial relocation offset. If the
symbol pointer is zero, then the section provided is looked up.
address
The address field gives the offset in bytes from the base of
the section data which owns the relocation record to the first
byte of relocatable information. The actual data relocated
will be relative to this point; for example, a relocation
type which modifies the bottom two bytes of a four byte word
would not touch the first byte pointed to in a big endian
world.
addend
The addend is a value provided by the back end to be added (!)
to the relocation offset. Its interpretation is dependent upon
the howto. For example, on the 68k the code:
char foo[];
main()
{
return foo[0x12345678];
}
Could be compiled into:
linkw fp,#-4
moveb @#12345678,d0
extbl d0
unlk fp
rts
This could create a reloc pointing to foo, but leave the
offset in the data, something like:
RELOCATION RECORDS FOR [.text]: offset type value 00000006 32 _foo 00000000 4e56 fffc ; linkw fp,#-4 00000004 1039 1234 5678 ; moveb @#12345678,d0 0000000a 49c0 ; extbl d0 0000000c 4e5e ; unlk fp 0000000e 4e75 ; rts
Using coff and an 88k, some instructions don't have enough space in them to represent the full address range, and pointers have to be loaded in two parts. So you'd get something like:
or.u r13,r0,hi16(_foo+0x12345678)
ld.b r2,r13,lo16(_foo+0x12345678)
jmp r1
This should create two relocs, both pointing to _foo, and with
0x12340000 in their addend field. The data would consist of:
RELOCATION RECORDS FOR [.text]: offset type value 00000002 HVRT16 _foo+0x12340000 00000006 LVRT16 _foo+0x12340000 00000000 5da05678 ; or.u r13,r0,0x5678 00000004 1c4d5678 ; ld.b r2,r13,0x5678 00000008 f400c001 ; jmp r1
The relocation routine digs out the value from the data, adds
it to the addend to get the original offset, and then adds the
value of _foo. Note that all 32 bits have to be kept around
somewhere, to cope with carry from bit 15 to bit 16.
One further example is the sparc and the a.out format. The sparc has a similar problem to the 88k, in that some instructions don't have room for an entire offset, but on the sparc the parts are created in odd sized lumps. The designers of the a.out format chose to not use the data within the section for storing part of the offset; all the offset is kept within the reloc. Anything in the data should be ignored.
save %sp,-112,%sp
sethi %hi(_foo+0x12345678),%g2
ldsb [%g2+%lo(_foo+0x12345678)],%i0
ret
restore
Both relocs contain a pointer to foo, and the offsets
contain junk.
RELOCATION RECORDS FOR [.text]: offset type value 00000004 HI22 _foo+0x12345678 00000008 LO10 _foo+0x12345678 00000000 9de3bf90 ; save %sp,-112,%sp 00000004 05000000 ; sethi %hi(_foo+0),%g2 00000008 f048a000 ; ldsb [%g2+%lo(_foo+0)],%i0 0000000c 81c7e008 ; ret 00000010 81e80000 ; restore
howto
The howto field can be imagined as a
relocation instruction. It is a pointer to a structure which
contains information on what to do with all of the other
information in the reloc record and data section. A back end
would normally have a relocation instruction set and turn
relocations into pointers to the correct structure on input -
but it would be possible to create each howto field on demand.
enum complain_overflowIndicates what sort of overflow checking should be done when performing a relocation.
enum complain_overflow
{
/* Do not complain on overflow. */
complain_overflow_dont,
/* Complain if the bitfield overflows, whether it is considered
as signed or unsigned. */
complain_overflow_bitfield,
/* Complain if the value overflows when considered as signed
number. */
complain_overflow_signed,
/* Complain if the value overflows when considered as an
unsigned number. */
complain_overflow_unsigned
};
reloc_howto_type
The reloc_howto_type is a structure which contains all the
information that libbfd needs to know to tie up a back end's data.
struct symbol_cache_entry; /* Forward declaration */
struct reloc_howto_struct
{
/* The type field has mainly a documentary use - the back end can
do what it wants with it, though normally the back end's
external idea of what a reloc number is stored
in this field. For example, a PC relative word relocation
in a coff environment has the type 023 - because that's
what the outside world calls a R_PCRWORD reloc. */
unsigned int type;
/* The value the final relocation is shifted right by. This drops
unwanted data from the relocation. */
unsigned int rightshift;
/* The size of the item to be relocated. This is *not* a
power-of-two measure. To get the number of bytes operated
on by a type of relocation, use bfd_get_reloc_size. */
int size;
/* The number of bits in the item to be relocated. This is used
when doing overflow checking. */
unsigned int bitsize;
/* Notes that the relocation is relative to the location in the
data section of the addend. The relocation function will
subtract from the relocation value the address of the location
being relocated. */
boolean pc_relative;
/* The bit position of the reloc value in the destination.
The relocated value is left shifted by this amount. */
unsigned int bitpos;
/* What type of overflow error should be checked for when
relocating. */
enum complain_overflow complain_on_overflow;
/* If this field is non null, then the supplied function is
called rather than the normal function. This allows really
strange relocation methods to be accomodated (e.g., i960 callj
instructions). */
bfd_reloc_status_type (*special_function)
PARAMS ((bfd *abfd,
arelent *reloc_entry,
struct symbol_cache_entry *symbol,
PTR data,
asection *input_section,
bfd *output_bfd,
char **error_message));
/* The textual name of the relocation type. */
char *name;
/* When performing a partial link, some formats must modify the
relocations rather than the data - this flag signals this.*/
boolean partial_inplace;
/* The src_mask selects which parts of the read in data
are to be used in the relocation sum. E.g., if this was an 8 bit
bit of data which we read and relocated, this would be
0x000000ff. When we have relocs which have an addend, such as
sun4 extended relocs, the value in the offset part of a
relocating field is garbage so we never use it. In this case
the mask would be 0x00000000. */
bfd_vma src_mask;
/* The dst_mask selects which parts of the instruction are replaced
into the instruction. In most cases src_mask == dst_mask,
except in the above special case, where dst_mask would be
0x000000ff, and src_mask would be 0x00000000. */
bfd_vma dst_mask;
/* When some formats create PC relative instructions, they leave
the value of the pc of the place being relocated in the offset
slot of the instruction, so that a PC relative relocation can
be made just by adding in an ordinary offset (e.g., sun3 a.out).
Some formats leave the displacement part of an instruction
empty (e.g., m88k bcs); this flag signals the fact.*/
boolean pcrel_offset;
};
The HOWTO Macro
Description
The HOWTO define is horrible and will go away.
#define HOWTO(C, R,S,B, P, BI, O, SF, NAME, INPLACE, MASKSRC, MASKDST, PC) \
{(unsigned)C,R,S,B, P, BI, O,SF,NAME,INPLACE,MASKSRC,MASKDST,PC}
Description
And will be replaced with the totally magic way. But for the
moment, we are compatible, so do it this way.
#define NEWHOWTO( FUNCTION, NAME,SIZE,REL,IN) HOWTO(0,0,SIZE,0,REL,0,complain_overflow_dont,FUNCTION, NAME,false,0,0,IN)
Description
Helper routine to turn a symbol into a relocation value.
#define HOWTO_PREPARE(relocation, symbol) \
{ \
if (symbol != (asymbol *)NULL) { \
if (bfd_is_com_section (symbol->section)) { \
relocation = 0; \
} \
else { \
relocation = symbol->value; \
} \
} \
}
bfd_get_reloc_sizeSynopsis
unsigned int bfd_get_reloc_size (reloc_howto_type *);
Description
For a reloc_howto_type that operates on a fixed number of bytes,
this returns the number of bytes operated on.
arelent_chain
Description
How relocs are tied together in an asection:
typedef struct relent_chain {
arelent relent;
struct relent_chain *next;
} arelent_chain;
bfd_check_overflowSynopsis
bfd_reloc_status_type
bfd_check_overflow
(enum complain_overflow how,
unsigned int bitsize,
unsigned int rightshift,
bfd_vma relocation);
Description
Perform overflow checking on relocation which has bitsize
significant bits and will be shifted right by rightshift bits.
The result is either of bfd_reloc_ok or
bfd_reloc_overflow.
bfd_perform_relocationSynopsis
bfd_reloc_status_type
bfd_perform_relocation
(bfd *abfd,
arelent *reloc_entry,
PTR data,
asection *input_section,
bfd *output_bfd,
char **error_message);
Description
If output_bfd is supplied to this function, the
generated image will be relocatable; the relocations are
copied to the output file after they have been changed to
reflect the new state of the world. There are two ways of
reflecting the results of partial linkage in an output file:
by modifying the output data in place, and by modifying the
relocation record. Some native formats (e.g., basic a.out and
basic coff) have no way of specifying an addend in the
relocation type, so the addend has to go in the output data.
This is no big deal since in these formats the output data
slot will always be big enough for the addend. Complex reloc
types with addends were invented to solve just this problem.
The error_message argument is set to an error message if
this return bfd_reloc_dangerous.
bfd_install_relocationSynopsis
bfd_reloc_status_type
bfd_install_relocation
(bfd *abfd,
arelent *reloc_entry,
PTR data, bfd_vma data_start,
asection *input_section,
char **error_message);
Description
This looks remarkably like bfd_perform_relocation, except it
does not expect that the section contents have been filled in.
I.e., it's suitable for use when creating, rather than applying
a relocation.
For now, this function should be considered reserved for the assembler.
When an application wants to create a relocation, but doesn't know what the target machine might call it, it can find out by using this bit of code.
bfd_reloc_code_type
Description
The insides of a reloc code. The idea is that, eventually, there
will be one enumerator for every type of relocation we ever do.
Pass one of these values to bfd_reloc_type_lookup, and it'll
return a howto pointer.
This does mean that the application must determine the correct enumerator value; you can't get a howto pointer from a random set of attributes.
Here are the possible values for enum bfd_reloc_code_real:
The 24-bit relocation is used in some Intel 960 configurations.
The LITERAL reloc, at the LDQ instruction, refers to the .lita section symbol. The addend is ignored when writing, but is filled in with the file's GP value on reading, for convenience, as with the GPDISP_LO16 reloc.
The ELF_LITERAL reloc is somewhere between 16_GOTOFF and GPDISP_LO16. It should refer to the symbol to be referenced, as with 16_GOTOFF, but it generates output not based on the position within the .got section, but relative to the GP value chosen for the file during the final link stage.
The LITUSE reloc, on the instruction using the loaded address, gives information to the linker that it might be able to use to optimize away some literal section references. The symbol is ignored (read as the absolute section symbol), and the "addend" indicates the type of instruction using the register: 1 - "memory" fmt insn 2 - byte-manipulation (byte offset reg) 3 - jsr (target of branch)
The GNU linker currently doesn't do any of this optimizing.
typedef enum bfd_reloc_code_real bfd_reloc_code_real_type;
bfd_reloc_type_lookupSynopsis
reloc_howto_type * bfd_reloc_type_lookup (bfd *abfd, bfd_reloc_code_real_type code);
Description
Return a pointer to a howto structure which, when
invoked, will perform the relocation code on data from the
architecture noted.
bfd_default_reloc_type_lookupSynopsis
reloc_howto_type *bfd_default_reloc_type_lookup (bfd *abfd, bfd_reloc_code_real_type code);
Description
Provides a default relocation lookup routine for any architecture.
bfd_get_reloc_code_nameSynopsis
const char *bfd_get_reloc_code_name (bfd_reloc_code_real_type code);
Description
Provides a printable name for the supplied relocation code.
Useful mainly for printing error messages.
bfd_generic_relax_sectionSynopsis
boolean bfd_generic_relax_section
(bfd *abfd,
asection *section,
struct bfd_link_info *,
boolean *);
Description
Provides default handling for relaxing for back ends which
don't do relaxing -- i.e., does nothing.
bfd_generic_get_relocated_section_contentsSynopsis
bfd_byte *
bfd_generic_get_relocated_section_contents (bfd *abfd,
struct bfd_link_info *link_info,
struct bfd_link_order *link_order,
bfd_byte *data,
boolean relocateable,
asymbol **symbols);
Description
Provides default handling of relocation effort for back ends
which can't be bothered to do it efficiently.
Description
These are functions pertaining to core files.
bfd_core_file_failing_commandSynopsis
CONST char *bfd_core_file_failing_command(bfd *abfd);
Description
Return a read-only string explaining which program was running
when it failed and produced the core file abfd.
bfd_core_file_failing_signalSynopsis
int bfd_core_file_failing_signal(bfd *abfd);
Description
Returns the signal number which caused the core dump which
generated the file the BFD abfd is attached to.
core_file_matches_executable_pSynopsis
boolean core_file_matches_executable_p (bfd *core_bfd, bfd *exec_bfd);
Description
Return true if the core file attached to core_bfd
was generated by a run of the executable file attached to
exec_bfd, false otherwise.
Description
Each port of BFD to a different machine requries the creation
of a target back end. All the back end provides to the root
part of BFD is a structure containing pointers to functions
which perform certain low level operations on files. BFD
translates the applications's requests through a pointer into
calls to the back end routines.
When a file is opened with bfd_openr, its format and
target are unknown. BFD uses various mechanisms to determine
how to interpret the file. The operations performed are:
_bfd_new_bfd, then call bfd_find_target with the
target string supplied to bfd_openr and the new BFD pointer.
bfd_find_target,
look up the environment variable GNUTARGET and use
that as the target string.
NULL, or the target string is
default, then use the first item in the target vector
as the target type, and set target_defaulted in the BFD to
cause bfd_check_format to loop through all the targets.
See section bfd_target. See section File formats.
bfd_error_invalid_target to
bfd_openr.
bfd_openr attempts to open the file using
bfd_open_file, and returns the BFD.
Once the BFD has been opened and the target selected, the file
format may be determined. This is done by calling
bfd_check_format on the BFD with a suggested format.
If target_defaulted has been set, each possible target
type is tried to see if it recognizes the specified format.
bfd_check_format returns true when the caller guesses right.
Description
This structure contains everything that BFD knows about a
target. It includes things like its byte order, name, and which
routines to call to do various operations.
Every BFD points to a target structure with its xvec
member.
The macros below are used to dispatch to functions through the
bfd_target vector. They are used in a number of macros further
down in `bfd.h', and are also used when calling various
routines by hand inside the BFD implementation. The arglist
argument must be parenthesized; it contains all the arguments
to the called function.
They make the documentation (more) unpleasant to read, so if someone wants to fix this and not break the above, please do.
#define BFD_SEND(bfd, message, arglist) \
((*((bfd)->xvec->message)) arglist)
#ifdef DEBUG_BFD_SEND
#undef BFD_SEND
#define BFD_SEND(bfd, message, arglist) \
(((bfd) && (bfd)->xvec && (bfd)->xvec->message) ? \
((*((bfd)->xvec->message)) arglist) : \
(bfd_assert (__FILE__,__LINE__), NULL))
#endif
For operations which index on the BFD format:
#define BFD_SEND_FMT(bfd, message, arglist) \
(((bfd)->xvec->message[(int)((bfd)->format)]) arglist)
#ifdef DEBUG_BFD_SEND
#undef BFD_SEND_FMT
#define BFD_SEND_FMT(bfd, message, arglist) \
(((bfd) && (bfd)->xvec && (bfd)->xvec->message) ? \
(((bfd)->xvec->message[(int)((bfd)->format)]) arglist) : \
(bfd_assert (__FILE__,__LINE__), NULL))
#endif
This is the structure which defines the type of BFD this is. The
xvec member of the struct bfd itself points here. Each
module that implements access to a different target under BFD,
defines one of these.
FIXME, these names should be rationalised with the names of the entry points which call them. Too bad we can't have one macro to define them both!
enum bfd_flavour {
bfd_target_unknown_flavour,
bfd_target_aout_flavour,
bfd_target_coff_flavour,
bfd_target_ecoff_flavour,
bfd_target_elf_flavour,
bfd_target_ieee_flavour,
bfd_target_nlm_flavour,
bfd_target_oasys_flavour,
bfd_target_tekhex_flavour,
bfd_target_srec_flavour,
bfd_target_ihex_flavour,
bfd_target_som_flavour,
bfd_target_os9k_flavour,
bfd_target_versados_flavour,
bfd_target_msdos_flavour,
bfd_target_evax_flavour
};
enum bfd_endian { BFD_ENDIAN_BIG, BFD_ENDIAN_LITTLE, BFD_ENDIAN_UNKNOWN };
/* Forward declaration. */
typedef struct bfd_link_info _bfd_link_info;
typedef struct bfd_target
{
Identifies the kind of target, e.g., SunOS4, Ultrix, etc.
char *name;
The "flavour" of a back end is a general indication about the contents of a file.
enum bfd_flavour flavour;
The order of bytes within the data area of a file.
enum bfd_endian byteorder;
The order of bytes within the header parts of a file.
enum bfd_endian header_byteorder;
A mask of all the flags which an executable may have set -
from the set BFD_NO_FLAGS, HAS_RELOC, ...D_PAGED.
flagword object_flags;
A mask of all the flags which a section may have set - from
the set SEC_NO_FLAGS, SEC_ALLOC, ...SET_NEVER_LOAD.
flagword section_flags;
The character normally found at the front of a symbol (if any), perhaps `_'.
char symbol_leading_char;
The pad character for file names within an archive header.
char ar_pad_char;
The maximum number of characters in an archive header.
unsigned short ar_max_namelen;
Entries for byte swapping for data. These are different from the other entry points, since they don't take a BFD asthe first argument. Certain other handlers could do the same.
bfd_vma (*bfd_getx64) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_getx_signed_64) PARAMS ((const bfd_byte *)); void (*bfd_putx64) PARAMS ((bfd_vma, bfd_byte *)); bfd_vma (*bfd_getx32) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_getx_signed_32) PARAMS ((const bfd_byte *)); void (*bfd_putx32) PARAMS ((bfd_vma, bfd_byte *)); bfd_vma (*bfd_getx16) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_getx_signed_16) PARAMS ((const bfd_byte *)); void (*bfd_putx16) PARAMS ((bfd_vma, bfd_byte *));
Byte swapping for the headers
bfd_vma (*bfd_h_getx64) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_h_getx_signed_64) PARAMS ((const bfd_byte *)); void (*bfd_h_putx64) PARAMS ((bfd_vma, bfd_byte *)); bfd_vma (*bfd_h_getx32) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_h_getx_signed_32) PARAMS ((const bfd_byte *)); void (*bfd_h_putx32) PARAMS ((bfd_vma, bfd_byte *)); bfd_vma (*bfd_h_getx16) PARAMS ((const bfd_byte *)); bfd_signed_vma (*bfd_h_getx_signed_16) PARAMS ((const bfd_byte *)); void (*bfd_h_putx16) PARAMS ((bfd_vma, bfd_byte *));
Format dependent routines: these are vectors of entry points within the target vector structure, one for each format to check.
Check the format of a file being read. Return a bfd_target * or zero.
const struct bfd_target *(*_bfd_check_format[bfd_type_end]) PARAMS ((bfd *));
Set the format of a file being written.
boolean (*_bfd_set_format[bfd_type_end]) PARAMS ((bfd *));
Write cached information into a file being written, at bfd_close.
boolean (*_bfd_write_contents[bfd_type_end]) PARAMS ((bfd *));
The general target vector.
/* Generic entry points. */
#define BFD_JUMP_TABLE_GENERIC(NAME)\
CAT(NAME,_close_and_cleanup),\
CAT(NAME,_bfd_free_cached_info),\
CAT(NAME,_new_section_hook),\
CAT(NAME,_get_section_contents),\
CAT(NAME,_get_section_contents_in_window)
/* Called when the BFD is being closed to do any necessary cleanup. */
boolean (*_close_and_cleanup) PARAMS ((bfd *));
/* Ask the BFD to free all cached information. */
boolean (*_bfd_free_cached_info) PARAMS ((bfd *));
/* Called when a new section is created. */
boolean (*_new_section_hook) PARAMS ((bfd *, sec_ptr));
/* Read the contents of a section. */
boolean (*_bfd_get_section_contents) PARAMS ((bfd *, sec_ptr, PTR,
file_ptr, bfd_size_type));
boolean (*_bfd_get_section_contents_in_window)
PARAMS ((bfd *, sec_ptr, bfd_window *,
file_ptr, bfd_size_type));
/* Entry points to copy private data. */
#define BFD_JUMP_TABLE_COPY(NAME)\
CAT(NAME,_bfd_copy_private_bfd_data),\
CAT(NAME,_bfd_merge_private_bfd_data),\
CAT(NAME,_bfd_copy_private_section_data),\
CAT(NAME,_bfd_copy_private_symbol_data),\
CAT(NAME,_bfd_set_private_flags),\
CAT(NAME,_bfd_print_private_bfd_data)\
/* Called to copy BFD general private data from one object file
to another. */
boolean (*_bfd_copy_private_bfd_data) PARAMS ((bfd *, bfd *));
/* Called to merge BFD general private data from one object file
to a common output file when linking. */
boolean (*_bfd_merge_private_bfd_data) PARAMS ((bfd *, bfd *));
/* Called to copy BFD private section data from one object file
to another. */
boolean (*_bfd_copy_private_section_data) PARAMS ((bfd *, sec_ptr,
bfd *, sec_ptr));
/* Called to copy BFD private symbol data from one symbol
to another. */
boolean (*_bfd_copy_private_symbol_data) PARAMS ((bfd *, asymbol *,
bfd *, asymbol *));
/* Called to set private backend flags */
boolean (*_bfd_set_private_flags) PARAMS ((bfd *, flagword));
/* Called to print private BFD data */
boolean (*_bfd_print_private_bfd_data) PARAMS ((bfd *, PTR));
/* Core file entry points. */
#define BFD_JUMP_TABLE_CORE(NAME)\
CAT(NAME,_core_file_failing_command),\
CAT(NAME,_core_file_failing_signal),\
CAT(NAME,_core_file_matches_executable_p)
char * (*_core_file_failing_command) PARAMS ((bfd *));
int (*_core_file_failing_signal) PARAMS ((bfd *));
boolean (*_core_file_matches_executable_p) PARAMS ((bfd *, bfd *));
/* Archive entry points. */
#define BFD_JUMP_TABLE_ARCHIVE(NAME)\
CAT(NAME,_slurp_armap),\
CAT(NAME,_slurp_extended_name_table),\
CAT(NAME,_construct_extended_name_table),\
CAT(NAME,_truncate_arname),\
CAT(NAME,_write_armap),\
CAT(NAME,_read_ar_hdr),\
CAT(NAME,_openr_next_archived_file),\
CAT(NAME,_get_elt_at_index),\
CAT(NAME,_generic_stat_arch_elt),\
CAT(NAME,_update_armap_timestamp)
boolean (*_bfd_slurp_armap) PARAMS ((bfd *));
boolean (*_bfd_slurp_extended_name_table) PARAMS ((bfd *));
boolean (*_bfd_construct_extended_name_table)
PARAMS ((bfd *, char **, bfd_size_type *, const char **));
void (*_bfd_truncate_arname) PARAMS ((bfd *, CONST char *, char *));
boolean (*write_armap) PARAMS ((bfd *arch,
unsigned int elength,
struct orl *map,
unsigned int orl_count,
int stridx));
PTR (*_bfd_read_ar_hdr_fn) PARAMS ((bfd *));
bfd * (*openr_next_archived_file) PARAMS ((bfd *arch, bfd *prev));
#define bfd_get_elt_at_index(b,i) BFD_SEND(b, _bfd_get_elt_at_index, (b,i))
bfd * (*_bfd_get_elt_at_index) PARAMS ((bfd *, symindex));
int (*_bfd_stat_arch_elt) PARAMS ((bfd *, struct stat *));
boolean (*_bfd_update_armap_timestamp) PARAMS ((bfd *));
/* Entry points used for symbols. */
#define BFD_JUMP_TABLE_SYMBOLS(NAME)\
CAT(NAME,_get_symtab_upper_bound),\
CAT(NAME,_get_symtab),\
CAT(NAME,_make_empty_symbol),\
CAT(NAME,_print_symbol),\
CAT(NAME,_get_symbol_info),\
CAT(NAME,_bfd_is_local_label_name),\
CAT(NAME,_get_lineno),\
CAT(NAME,_find_nearest_line),\
CAT(NAME,_bfd_make_debug_symbol),\
CAT(NAME,_read_minisymbols),\
CAT(NAME,_minisymbol_to_symbol)
long (*_bfd_get_symtab_upper_bound) PARAMS ((bfd *));
long (*_bfd_canonicalize_symtab) PARAMS ((bfd *,
struct symbol_cache_entry **));
struct symbol_cache_entry *
(*_bfd_make_empty_symbol) PARAMS ((bfd *));
void (*_bfd_print_symbol) PARAMS ((bfd *, PTR,
struct symbol_cache_entry *,
bfd_print_symbol_type));
#define bfd_print_symbol(b,p,s,e) BFD_SEND(b, _bfd_print_symbol, (b,p,s,e))
void (*_bfd_get_symbol_info) PARAMS ((bfd *,
struct symbol_cache_entry *,
symbol_info *));
#define bfd_get_symbol_info(b,p,e) BFD_SEND(b, _bfd_get_symbol_info, (b,p,e))
boolean (*_bfd_is_local_label_name) PARAMS ((bfd *, const char *));
alent * (*_get_lineno) PARAMS ((bfd *, struct symbol_cache_entry *));
boolean (*_bfd_find_nearest_line) PARAMS ((bfd *abfd,
struct sec *section, struct symbol_cache_entry **symbols,
bfd_vma offset, CONST char **file, CONST char **func,
unsigned int *line));
/* Back-door to allow format-aware applications to create debug symbols
while using BFD for everything else. Currently used by the assembler
when creating COFF files. */
asymbol * (*_bfd_make_debug_symbol) PARAMS ((
bfd *abfd,
void *ptr,
unsigned long size));
#define bfd_read_minisymbols(b, d, m, s) \
BFD_SEND (b, _read_minisymbols, (b, d, m, s))
long (*_read_minisymbols) PARAMS ((bfd *, boolean, PTR *,
unsigned int *));
#define bfd_minisymbol_to_symbol(b, d, m, f) \
BFD_SEND (b, _minisymbol_to_symbol, (b, d, m, f))
asymbol *(*_minisymbol_to_symbol) PARAMS ((bfd *, boolean, const PTR,
asymbol *));
/* Routines for relocs. */
#define BFD_JUMP_TABLE_RELOCS(NAME)\
CAT(NAME,_get_reloc_upper_bound),\
CAT(NAME,_canonicalize_reloc),\
CAT(NAME,_bfd_reloc_type_lookup)
long (*_get_reloc_upper_bound) PARAMS ((bfd *, sec_ptr));
long (*_bfd_canonicalize_reloc) PARAMS ((bfd *, sec_ptr, arelent **,
struct symbol_cache_entry **));
/* See documentation on reloc types. */
reloc_howto_type *
(*reloc_type_lookup) PARAMS ((bfd *abfd,
bfd_reloc_code_real_type code));
/* Routines used when writing an object file. */
#define BFD_JUMP_TABLE_WRITE(NAME)\
CAT(NAME,_set_arch_mach),\
CAT(NAME,_set_section_contents)
boolean (*_bfd_set_arch_mach) PARAMS ((bfd *, enum bfd_architecture,
unsigned long));
boolean (*_bfd_set_section_contents) PARAMS ((bfd *, sec_ptr, PTR,
file_ptr, bfd_size_type));
/* Routines used by the linker. */
#define BFD_JUMP_TABLE_LINK(NAME)\
CAT(NAME,_sizeof_headers),\
CAT(NAME,_bfd_get_relocated_section_contents),\
CAT(NAME,_bfd_relax_section),\
CAT(NAME,_bfd_link_hash_table_create),\
CAT(NAME,_bfd_link_add_symbols),\
CAT(NAME,_bfd_final_link),\
CAT(NAME,_bfd_link_split_section)
int (*_bfd_sizeof_headers) PARAMS ((bfd *, boolean));
bfd_byte * (*_bfd_get_relocated_section_contents) PARAMS ((bfd *,
struct bfd_link_info *, struct bfd_link_order *,
bfd_byte *data, boolean relocateable,
struct symbol_cache_entry **));
boolean (*_bfd_relax_section) PARAMS ((bfd *, struct sec *,
struct bfd_link_info *, boolean *again));
/* Create a hash table for the linker. Different backends store
different information in this table. */
struct bfd_link_hash_table *(*_bfd_link_hash_table_create) PARAMS ((bfd *));
/* Add symbols from this object file into the hash table. */
boolean (*_bfd_link_add_symbols) PARAMS ((bfd *, struct bfd_link_info *));
/* Do a link based on the link_order structures attached to each
section of the BFD. */
boolean (*_bfd_final_link) PARAMS ((bfd *, struct bfd_link_info *));
/* Should this section be split up into smaller pieces during linking. */
boolean (*_bfd_link_split_section) PARAMS ((bfd *, struct sec *));
/* Routines to handle dynamic symbols and relocs. */
#define BFD_JUMP_TABLE_DYNAMIC(NAME)\
CAT(NAME,_get_dynamic_symtab_upper_bound),\
CAT(NAME,_canonicalize_dynamic_symtab),\
CAT(NAME,_get_dynamic_reloc_upper_bound),\
CAT(NAME,_canonicalize_dynamic_reloc)
/* Get the amount of memory required to hold the dynamic symbols. */
long (*_bfd_get_dynamic_symtab_upper_bound) PARAMS ((bfd *));
/* Read in the dynamic symbols. */
long (*_bfd_canonicalize_dynamic_symtab)
PARAMS ((bfd *, struct symbol_cache_entry **));
/* Get the amount of memory required to hold the dynamic relocs. */
long (*_bfd_get_dynamic_reloc_upper_bound) PARAMS ((bfd *));
/* Read in the dynamic relocs. */
long (*_bfd_canonicalize_dynamic_reloc)
PARAMS ((bfd *, arelent **, struct symbol_cache_entry **));
Data for use by back-end routines, which isn't generic enough to belong in this structure.
PTR backend_data; } bfd_target;
bfd_set_default_targetSynopsis
boolean bfd_set_default_target (const char *name);
Description
Set the default target vector to use when recognizing a BFD.
This takes the name of the target, which may be a BFD target
name or a configuration triplet.
bfd_find_targetSynopsis
const bfd_target *bfd_find_target(CONST char *target_name, bfd *abfd);
Description
Return a pointer to the transfer vector for the object target
named target_name. If target_name is NULL, choose the
one in the environment variable GNUTARGET; if that is null or not
defined, then choose the first entry in the target list.
Passing in the string "default" or setting the environment
variable to "default" will cause the first entry in the target
list to be returned, and "target_defaulted" will be set in the
BFD. This causes bfd_check_format to loop over all the
targets to find the one that matches the file being read.
bfd_target_listSynopsis
const char **bfd_target_list(void);
Description
Return a freshly malloced NULL-terminated
vector of the names of all the valid BFD targets. Do not
modify the names.
BFD keeps one atom in a BFD describing the
architecture of the data attached to the BFD: a pointer to a
bfd_arch_info_type.
Pointers to structures can be requested independently of a BFD so that an architecture's information can be interrogated without access to an open BFD.
The architecture information is provided by each architecture package.
The set of default architectures is selected by the macro
SELECT_ARCHITECTURES. This is normally set up in the
`config/target.mt' file of your choice. If the name is not
defined, then all the architectures supported are included.
When BFD starts up, all the architectures are called with an initialize method. It is up to the architecture back end to insert as many items into the list of architectures as it wants to; generally this would be one for each machine and one for the default case (an item with a machine field of 0).
BFD's idea of an architecture is implemented in `archures.c'.
Description
This enum gives the object file's CPU architecture, in a
global sense--i.e., what processor family does it belong to?
Another field indicates which processor within
the family is in use. The machine gives a number which
distinguishes different versions of the architecture,
containing, for example, 2 and 3 for Intel i960 KA and i960 KB,
and 68020 and 68030 for Motorola 68020 and 68030.
enum bfd_architecture
{
bfd_arch_unknown, /* File arch not known */
bfd_arch_obscure, /* Arch known, not one of these */
bfd_arch_m68k, /* Motorola 68xxx */
#define bfd_mach_m68000 1
#define bfd_mach_m68008 2
#define bfd_mach_m68010 3
#define bfd_mach_m68020 4
#define bfd_mach_m68030 5
#define bfd_mach_m68040 6
#define bfd_mach_m68060 7
bfd_arch_vax, /* DEC Vax */
bfd_arch_i960, /* Intel 960 */
/* The order of the following is important.
lower number indicates a machine type that
only accepts a subset of the instructions
available to machines with higher numbers.
The exception is the "ca", which is
incompatible with all other machines except
"core". */
#define bfd_mach_i960_core 1
#define bfd_mach_i960_ka_sa 2
#define bfd_mach_i960_kb_sb 3
#define bfd_mach_i960_mc 4
#define bfd_mach_i960_xa 5
#define bfd_mach_i960_ca 6
#define bfd_mach_i960_jx 7
#define bfd_mach_i960_hx 8
bfd_arch_a29k, /* AMD 29000 */
bfd_arch_sparc, /* SPARC */
#define bfd_mach_sparc 1
/* The difference between v8plus and v9 is that v9 is a true 64 bit env. */
#define bfd_mach_sparc_sparclet 2
#define bfd_mach_sparc_sparclite 3
#define bfd_mach_sparc_v8plus 4
#define bfd_mach_sparc_v8plusa 5 /* with ultrasparc add'ns */
#define bfd_mach_sparc_v9 6
#define bfd_mach_sparc_v9a 7 /* with ultrasparc add'ns */
/* Nonzero if MACH has the v9 instruction set. */
#define bfd_mach_sparc_v9_p(mach) \
((mach) >= bfd_mach_sparc_v8plus && (mach) <= bfd_mach_sparc_v9a)
bfd_arch_mips, /* MIPS Rxxxx */
#define bfd_mach_mips3000 3000
#define bfd_mach_mips3900 3900
#define bfd_mach_mips4000 4000
#define bfd_mach_mips4010 4010
#define bfd_mach_mips4100 4100
#define bfd_mach_mips4300 4300
#define bfd_mach_mips4400 4400
#define bfd_mach_mips4600 4600
#define bfd_mach_mips4650 4650
#define bfd_mach_mips5000 5000
#define bfd_mach_mips6000 6000
#define bfd_mach_mips8000 8000
#define bfd_mach_mips10000 10000
#define bfd_mach_mips16 16
bfd_arch_i386, /* Intel 386 */
#define bfd_mach_i386_i386 0
#define bfd_mach_i386_i8086 1
bfd_arch_we32k, /* AT&T WE32xxx */
bfd_arch_tahoe, /* CCI/Harris Tahoe */
bfd_arch_i860, /* Intel 860 */
bfd_arch_romp, /* IBM ROMP PC/RT */
bfd_arch_alliant, /* Alliant */
bfd_arch_convex, /* Convex */
bfd_arch_m88k, /* Motorola 88xxx */
bfd_arch_pyramid, /* Pyramid Technology */
bfd_arch_h8300, /* Hitachi H8/300 */
#define bfd_mach_h8300 1
#define bfd_mach_h8300h 2
#define bfd_mach_h8300s 3
bfd_arch_powerpc, /* PowerPC */
bfd_arch_rs6000, /* IBM RS/6000 */
bfd_arch_hppa, /* HP PA RISC */
bfd_arch_d10v, /* Mitsubishi D10V */
bfd_arch_z8k, /* Zilog Z8000 */
#define bfd_mach_z8001 1
#define bfd_mach_z8002 2
bfd_arch_h8500, /* Hitachi H8/500 */
bfd_arch_sh, /* Hitachi SH */
#define bfd_mach_sh 0
#define bfd_mach_sh3 0x30
#define bfd_mach_sh3e 0x3e
#define bfd_mach_sh4 0x40
bfd_arch_alpha, /* Dec Alpha */
bfd_arch_arm, /* Advanced Risc Machines ARM */
#define bfd_mach_arm_2 1
#define bfd_mach_arm_2a 2
#define bfd_mach_arm_3 3
#define bfd_mach_arm_3M 4
#define bfd_mach_arm_4 5
#define bfd_mach_arm_4T 6
bfd_arch_ns32k, /* National Semiconductors ns32000 */
bfd_arch_w65, /* WDC 65816 */
bfd_arch_tic30, /* Texas Instruments TMS320C30 */
bfd_arch_v850, /* NEC V850 */
#define bfd_mach_v850 0
bfd_arch_arc, /* Argonaut RISC Core */
#define bfd_mach_arc_base 0
bfd_arch_m32r, /* Mitsubishi M32R/D */
#define bfd_mach_m32r 0 /* backwards compatibility */
bfd_arch_mn10200, /* Matsushita MN10200 */
bfd_arch_mn10300, /* Matsushita MN10300 */
bfd_arch_last
};
Description
This structure contains information on architectures for use
within BFD.
typedef struct bfd_arch_info
{
int bits_per_word;
int bits_per_address;
int bits_per_byte;
enum bfd_architecture arch;
unsigned long mach;
const char *arch_name;
const char *printable_name;
unsigned int section_align_power;
/* true if this is the default machine for the architecture */
boolean the_default;
const struct bfd_arch_info * (*compatible)
PARAMS ((const struct bfd_arch_info *a,
const struct bfd_arch_info *b));
boolean (*scan) PARAMS ((const struct bfd_arch_info *, const char *));
const struct bfd_arch_info *next;
} bfd_arch_info_type;
bfd_printable_nameSynopsis
const char *bfd_printable_name(bfd *abfd);
Description
Return a printable string representing the architecture and machine
from the pointer to the architecture info structure.
bfd_scan_archSynopsis
const bfd_arch_info_type *bfd_scan_arch(const char *string);
Description
Figure out if BFD supports any cpu which could be described with
the name string. Return a pointer to an arch_info
structure if a machine is found, otherwise NULL.
bfd_arch_listSynopsis
const char **bfd_arch_list(void);
Description
Return a freshly malloced NULL-terminated vector of the names
of all the valid BFD architectures. Do not modify the names.
bfd_arch_get_compatibleSynopsis
const bfd_arch_info_type *bfd_arch_get_compatible(
const bfd *abfd,
const bfd *bbfd);
Description
Determine whether two BFDs'
architectures and machine types are compatible. Calculates
the lowest common denominator between the two architectures
and machine types implied by the BFDs and returns a pointer to
an arch_info structure describing the compatible machine.
bfd_default_arch_struct
Description
The bfd_default_arch_struct is an item of
bfd_arch_info_type which has been initialized to a fairly
generic state. A BFD starts life by pointing to this
structure, until the correct back end has determined the real
architecture of the file.
extern const bfd_arch_info_type bfd_default_arch_struct;
bfd_set_arch_infoSynopsis
void bfd_set_arch_info(bfd *abfd, const bfd_arch_info_type *arg);
Description
Set the architecture info of abfd to arg.
bfd_default_set_arch_machSynopsis
boolean bfd_default_set_arch_mach(bfd *abfd,
enum bfd_architecture arch,
unsigned long mach);
Description
Set the architecture and machine type in BFD abfd
to arch and mach. Find the correct
pointer to a structure and insert it into the arch_info
pointer.
bfd_get_archSynopsis
enum bfd_architecture bfd_get_arch(bfd *abfd);
Description
Return the enumerated type which describes the BFD abfd's
architecture.
bfd_get_machSynopsis
unsigned long bfd_get_mach(bfd *abfd);
Description
Return the long type which describes the BFD abfd's
machine.
bfd_arch_bits_per_byteSynopsis
unsigned int bfd_arch_bits_per_byte(bfd *abfd);
Description
Return the number of bits in one of the BFD abfd's
architecture's bytes.
bfd_arch_bits_per_addressSynopsis
unsigned int bfd_arch_bits_per_address(bfd *abfd);
Description
Return the number of bits in one of the BFD abfd's
architecture's addresses.
bfd_default_compatibleSynopsis
const bfd_arch_info_type *bfd_default_compatible
(const bfd_arch_info_type *a,
const bfd_arch_info_type *b);
Description
The default function for testing for compatibility.
bfd_default_scanSynopsis
boolean bfd_default_scan(const struct bfd_arch_info *info, const char *string);
Description
The default function for working out whether this is an
architecture hit and a machine hit.
bfd_get_arch_infoSynopsis
const bfd_arch_info_type * bfd_get_arch_info(bfd *abfd);
Description
Return the architecture info struct in abfd.
bfd_lookup_archSynopsis
const bfd_arch_info_type *bfd_lookup_arch
(enum bfd_architecture
arch,
unsigned long machine);
Description
Look for the architecure info structure which matches the
arguments arch and machine. A machine of 0 matches the
machine/architecture structure which marks itself as the
default.
bfd_printable_arch_machSynopsis
const char *bfd_printable_arch_mach (enum bfd_architecture arch, unsigned long machine);
Description
Return a printable string representing the architecture and
machine type.
This routine is depreciated.
bfd_openrSynopsis
bfd *bfd_openr(CONST char *filename, CONST char *target);
Description
Open the file filename (using fopen) with the target
target. Return a pointer to the created BFD.
Calls bfd_find_target, so target is interpreted as by
that function.
If NULL is returned then an error has occured. Possible errors
are bfd_error_no_memory, bfd_error_invalid_target or system_call error.
bfd_fdopenrSynopsis
bfd *bfd_fdopenr(CONST char *filename, CONST char *target, int fd);
Description
bfd_fdopenr is to bfd_fopenr much like fdopen is to fopen.
It opens a BFD on a file already described by the fd
supplied.
When the file is later bfd_closed, the file descriptor will be closed.
If the caller desires that this file descriptor be cached by BFD
(opened as needed, closed as needed to free descriptors for
other opens), with the supplied fd used as an initial
file descriptor (but subject to closure at any time), call
bfd_set_cacheable(bfd, 1) on the returned BFD. The default is to
assume no cacheing; the file descriptor will remain open until
bfd_close, and will not be affected by BFD operations on other
files.
Possible errors are bfd_error_no_memory, bfd_error_invalid_target and bfd_error_system_call.
bfd_openstreamrSynopsis
bfd *bfd_openstreamr(const char *, const char *, PTR);
Description
Open a BFD for read access on an existing stdio stream. When
the BFD is passed to bfd_close, the stream will be closed.
bfd_openwSynopsis
bfd *bfd_openw(CONST char *filename, CONST char *target);
Description
Create a BFD, associated with file filename, using the
file format target, and return a pointer to it.
Possible errors are bfd_error_system_call, bfd_error_no_memory,
bfd_error_invalid_target.
bfd_closeSynopsis
boolean bfd_close(bfd *abfd);
Description
Close a BFD. If the BFD was open for writing,
then pending operations are completed and the file written out
and closed. If the created file is executable, then
chmod is called to mark it as such.
All memory attached to the BFD is released.
The file descriptor associated with the BFD is closed (even
if it was passed in to BFD by bfd_fdopenr).
Returns
true is returned if all is ok, otherwise false.
bfd_close_all_doneSynopsis
boolean bfd_close_all_done(bfd *);
Description
Close a BFD. Differs from bfd_close
since it does not complete any pending operations. This
routine would be used if the application had just used BFD for
swapping and didn't want to use any of the writing code.
If the created file is executable, then chmod is called
to mark it as such.
All memory attached to the BFD is released.
Returns
true is returned if all is ok, otherwise false.
bfd_createSynopsis
bfd *bfd_create(CONST char *filename, bfd *templ);
Description
Create a new BFD in the manner of
bfd_openw, but without opening a file. The new BFD
takes the target from the target used by template. The
format is always set to bfd_object.
bfd_allocSynopsis
PTR bfd_alloc (bfd *abfd, size_t wanted);
Description
Allocate a block of wanted bytes of memory attached to
abfd and return a pointer to it.
Description
These routines are used within BFD.
They are not intended for export, but are documented here for
completeness.
bfd_write_bigendian_4byte_intSynopsis
void bfd_write_bigendian_4byte_int(bfd *abfd, int i);
Description
Write a 4 byte integer i to the output BFD abfd, in big
endian order regardless of what else is going on. This is useful in
archives.
bfd_put_sizebfd_get_size
Description
These macros as used for reading and writing raw data in
sections; each access (except for bytes) is vectored through
the target format of the BFD and mangled accordingly. The
mangling performs any necessary endian translations and
removes alignment restrictions. Note that types accepted and
returned by these macros are identical so they can be swapped
around in macros--for example, `libaout.h' defines GET_WORD
to either bfd_get_32 or bfd_get_64.
In the put routines, val must be a bfd_vma. If we are on a
system without prototypes, the caller is responsible for making
sure that is true, with a cast if necessary. We don't cast
them in the macro definitions because that would prevent lint
or gcc -Wall from detecting sins such as passing a pointer.
To detect calling these with less than a bfd_vma, use
gcc -Wconversion on a host with 64 bit bfd_vma's.
/* Byte swapping macros for user section data. */
#define bfd_put_8(abfd, val, ptr) \
(*((unsigned char *)(ptr)) = (unsigned char)(val))
#define bfd_put_signed_8 \
bfd_put_8
#define bfd_get_8(abfd, ptr) \
(*(unsigned char *)(ptr))
#define bfd_get_signed_8(abfd, ptr) \
((*(unsigned char *)(ptr) ^ 0x80) - 0x80)
#define bfd_put_16(abfd, val, ptr) \
BFD_SEND(abfd, bfd_putx16, ((val),(ptr)))
#define bfd_put_signed_16 \
bfd_put_16
#define bfd_get_16(abfd, ptr) \
BFD_SEND(abfd, bfd_getx16, (ptr))
#define bfd_get_signed_16(abfd, ptr) \
BFD_SEND (abfd, bfd_getx_signed_16, (ptr))
#define bfd_put_32(abfd, val, ptr) \
BFD_SEND(abfd, bfd_putx32, ((val),(ptr)))
#define bfd_put_signed_32 \
bfd_put_32
#define bfd_get_32(abfd, ptr) \
BFD_SEND(abfd, bfd_getx32, (ptr))
#define bfd_get_signed_32(abfd, ptr) \
BFD_SEND(abfd, bfd_getx_signed_32, (ptr))
#define bfd_put_64(abfd, val, ptr) \
BFD_SEND(abfd, bfd_putx64, ((val), (ptr)))
#define bfd_put_signed_64 \
bfd_put_64
#define bfd_get_64(abfd, ptr) \
BFD_SEND(abfd, bfd_getx64, (ptr))
#define bfd_get_signed_64(abfd, ptr) \
BFD_SEND(abfd, bfd_getx_signed_64, (ptr))
bfd_h_put_size
Description
These macros have the same function as their bfd_get_x
bretheren, except that they are used for removing information
for the header records of object files. Believe it or not,
some object files keep their header records in big endian
order and their data in little endian order.
/* Byte swapping macros for file header data. */
#define bfd_h_put_8(abfd, val, ptr) \
bfd_put_8 (abfd, val, ptr)
#define bfd_h_put_signed_8(abfd, val, ptr) \
bfd_put_8 (abfd, val, ptr)
#define bfd_h_get_8(abfd, ptr) \
bfd_get_8 (abfd, ptr)
#define bfd_h_get_signed_8(abfd, ptr) \
bfd_get_signed_8 (abfd, ptr)
#define bfd_h_put_16(abfd, val, ptr) \
BFD_SEND(abfd, bfd_h_putx16,(val,ptr))
#define bfd_h_put_signed_16 \
bfd_h_put_16
#define bfd_h_get_16(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx16,(ptr))
#define bfd_h_get_signed_16(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx_signed_16, (ptr))
#define bfd_h_put_32(abfd, val, ptr) \
BFD_SEND(abfd, bfd_h_putx32,(val,ptr))
#define bfd_h_put_signed_32 \
bfd_h_put_32
#define bfd_h_get_32(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx32,(ptr))
#define bfd_h_get_signed_32(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx_signed_32, (ptr))
#define bfd_h_put_64(abfd, val, ptr) \
BFD_SEND(abfd, bfd_h_putx64,(val, ptr))
#define bfd_h_put_signed_64 \
bfd_h_put_64
#define bfd_h_get_64(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx64,(ptr))
#define bfd_h_get_signed_64(abfd, ptr) \
BFD_SEND(abfd, bfd_h_getx_signed_64, (ptr))
bfd_log2Synopsis
unsigned int bfd_log2(bfd_vma x);
Description
Return the log base 2 of the value supplied, rounded up. E.g., an
x of 1025 returns 11.
The file caching mechanism is embedded within BFD and allows
the application to open as many BFDs as it wants without
regard to the underlying operating system's file descriptor
limit (often as low as 20 open files). The module in
cache.c maintains a least recently used list of
BFD_CACHE_MAX_OPEN files, and exports the name
bfd_cache_lookup, which runs around and makes sure that
the required BFD is open. If not, then it chooses a file to
close, closes it and opens the one wanted, returning its file
handle.
BFD_CACHE_MAX_OPEN macro
Description
The maximum number of files which the cache will keep open at
one time.
#define BFD_CACHE_MAX_OPEN 10
bfd_last_cacheSynopsis
extern bfd *bfd_last_cache;
Description
Zero, or a pointer to the topmost BFD on the chain. This is
used by the bfd_cache_lookup macro in `libbfd.h' to
determine when it can avoid a function call.
bfd_cache_lookup
Description
Check to see if the required BFD is the same as the last one
looked up. If so, then it can use the stream in the BFD with
impunity, since it can't have changed since the last lookup;
otherwise, it has to perform the complicated lookup function.
#define bfd_cache_lookup(x) \
((x)==bfd_last_cache? \
(FILE*)(bfd_last_cache->iostream): \
bfd_cache_lookup_worker(x))
bfd_cache_initSynopsis
boolean bfd_cache_init (bfd *abfd);
Description
Add a newly opened BFD to the cache.
bfd_cache_closeSynopsis
boolean bfd_cache_close (bfd *abfd);
Description
Remove the BFD abfd from the cache. If the attached file is open,
then close it too.
Returns
false is returned if closing the file fails, true is
returned if all is well.
bfd_open_fileSynopsis
FILE* bfd_open_file(bfd *abfd);
Description
Call the OS to open a file for abfd. Return the FILE *
(possibly NULL) that results from this operation. Set up the
BFD so that future accesses know the file is open. If the FILE *
returned is NULL, then it won't have been put in the
cache, so it won't have to be removed from it.
bfd_cache_lookup_workerSynopsis
FILE *bfd_cache_lookup_worker(bfd *abfd);
Description
Called when the macro bfd_cache_lookup fails to find a
quick answer. Find a file descriptor for abfd. If
necessary, it open it. If there are already more than
BFD_CACHE_MAX_OPEN files open, it tries to close one first, to
avoid running out of file descriptors.
The linker uses three special entry points in the BFD target vector. It is not necessary to write special routines for these entry points when creating a new BFD back end, since generic versions are provided. However, writing them can speed up linking and make it use significantly less runtime memory.
The first routine creates a hash table used by the other routines. The second routine adds the symbols from an object file to the hash table. The third routine takes all the object files and links them together to create the output file. These routines are designed so that the linker proper does not need to know anything about the symbols in the object files that it is linking. The linker merely arranges the sections as directed by the linker script and lets BFD handle the details of symbols and relocs.
The second routine and third routines are passed a pointer to
a struct bfd_link_info structure (defined in
bfdlink.h) which holds information relevant to the link,
including the linker hash table (which was created by the
first routine) and a set of callback functions to the linker
proper.
The generic linker routines are in linker.c, and use the
header file genlink.h. As of this writing, the only back
ends which have implemented versions of these routines are
a.out (in aoutx.h) and ECOFF (in ecoff.c). The a.out
routines are used as examples throughout this section.
The linker routines must create a hash table, which must be
derived from struct bfd_link_hash_table described in
bfdlink.c. See section Hash Tables for information on how to
create a derived hash table. This entry point is called using
the target vector of the linker output file.
The _bfd_link_hash_table_create entry point must allocate
and initialize an instance of the desired hash table. If the
back end does not require any additional information to be
stored with the entries in the hash table, the entry point may
simply create a struct bfd_link_hash_table. Most likely,
however, some additional information will be needed.
For example, with each entry in the hash table the a.out
linker keeps the index the symbol has in the final output file
(this index number is used so that when doing a relocateable
link the symbol index used in the output file can be quickly
filled in when copying over a reloc). The a.out linker code
defines the required structures and functions for a hash table
derived from struct bfd_link_hash_table. The a.out linker
hash table is created by the function
NAME(aout,link_hash_table_create); it simply allocates
space for the hash table, initializes it, and returns a
pointer to it.
When writing the linker routines for a new back end, you will generally not know exactly which fields will be required until you have finished. You should simply create a new hash table which defines no additional fields, and then simply add fields as they become necessary.
The linker proper will call the _bfd_link_add_symbols
entry point for each object file or archive which is to be
linked (typically these are the files named on the command
line, but some may also come from the linker script). The
entry point is responsible for examining the file. For an
object file, BFD must add any relevant symbol information to
the hash table. For an archive, BFD must determine which
elements of the archive should be used and adding them to the
link.
The a.out version of this entry point is
NAME(aout,link_add_symbols).
Normally all the files involved in a link will be of the same
format, but it is also possible to link together different
format object files, and the back end must support that. The
_bfd_link_add_symbols entry point is called via the target
vector of the file to be added. This has an important
consequence: the function may not assume that the hash table
is the type created by the corresponding
_bfd_link_hash_table_create vector. All the
_bfd_link_add_symbols function can assume about the hash
table is that it is derived from struct
bfd_link_hash_table.
Sometimes the _bfd_link_add_symbols function must store
some information in the hash table entry to be used by the
_bfd_final_link function. In such a case the creator
field of the hash table must be checked to make sure that the
hash table was created by an object file of the same format.
The _bfd_final_link routine must be prepared to handle a
hash entry without any extra information added by the
_bfd_link_add_symbols function. A hash entry without
extra information will also occur when the linker script
directs the linker to create a symbol. Note that, regardless
of how a hash table entry is added, all the fields will be
initialized to some sort of null value by the hash table entry
initialization function.
See ecoff_link_add_externals for an example of how to
check the creator field before saving information (in this
case, the ECOFF external symbol debugging information) in a
hash table entry.
When the _bfd_link_add_symbols routine is passed an object
file, it must add all externally visible symbols in that
object file to the hash table. The actual work of adding the
symbol to the hash table is normally handled by the function
_bfd_generic_link_add_one_symbol. The
_bfd_link_add_symbols routine is responsible for reading
all the symbols from the object file and passing the correct
information to _bfd_generic_link_add_one_symbol.
The _bfd_link_add_symbols routine should not use
bfd_canonicalize_symtab to read the symbols. The point of
providing this routine is to avoid the overhead of converting
the symbols into generic asymbol structures.
_bfd_generic_link_add_one_symbol handles the details of
combining common symbols, warning about multiple definitions,
and so forth. It takes arguments which describe the symbol to
add, notably symbol flags, a section, and an offset. The
symbol flags include such things as BSF_WEAK or
BSF_INDIRECT. The section is a section in the object
file, or something like bfd_und_section_ptr for an undefined
symbol or bfd_com_section_ptr for a common symbol.
If the _bfd_final_link routine is also going to need to
read the symbol information, the _bfd_link_add_symbols
routine should save it somewhere attached to the object file
BFD. However, the information should only be saved if the
keep_memory field of the info argument is true, so
that the -no-keep-memory linker switch is effective.
The a.out function which adds symbols from an object file is
aout_link_add_object_symbols, and most of the interesting
work is in aout_link_add_symbols. The latter saves
pointers to the hash tables entries created by
_bfd_generic_link_add_one_symbol indexed by symbol number,
so that the _bfd_final_link routine does not have to call
the hash table lookup routine to locate the entry.
When the _bfd_link_add_symbols routine is passed an
archive, it must look through the symbols defined by the
archive and decide which elements of the archive should be
included in the link. For each such element it must call the
add_archive_element linker callback, and it must add the
symbols from the object file to the linker hash table.
In most cases the work of looking through the symbols in the
archive should be done by the
_bfd_generic_link_add_archive_symbols function. This
function builds a hash table from the archive symbol table and
looks through the list of undefined symbols to see which
elements should be included.
_bfd_generic_link_add_archive_symbols is passed a function
to call to make the final decision about adding an archive
element to the link and to do the actual work of adding the
symbols to the linker hash table.
The function passed to
_bfd_generic_link_add_archive_symbols must read the
symbols of the archive element and decide whether the archive
element should be included in the link. If the element is to
be included, the add_archive_element linker callback
routine must be called with the element as an argument, and
the elements symbols must be added to the linker hash table
just as though the element had itself been passed to the
_bfd_link_add_symbols function.
When the a.out _bfd_link_add_symbols function receives an
archive, it calls _bfd_generic_link_add_archive_symbols
passing aout_link_check_archive_element as the function
argument. aout_link_check_archive_element calls
aout_link_check_ar_symbols. If the latter decides to add
the element (an element is only added if it provides a real,
non-common, definition for a previously undefined or common
symbol) it calls the add_archive_element callback and then
aout_link_check_archive_element calls
aout_link_add_symbols to actually add the symbols to the
linker hash table.
The ECOFF back end is unusual in that it does not normally
call _bfd_generic_link_add_archive_symbols, because ECOFF
archives already contain a hash table of symbols. The ECOFF
back end searches the archive itself to avoid the overhead of
creating a new hash table.
When all the input files have been processed, the linker calls
the _bfd_final_link entry point of the output BFD. This
routine is responsible for producing the final output file,
which has several aspects. It must relocate the contents of
the input sections and copy the data into the output sections.
It must build an output symbol table including any local
symbols from the input files and the global symbols from the
hash table. When producing relocateable output, it must
modify the input relocs and write them into the output file.
There may also be object format dependent work to be done.
The linker will also call the write_object_contents entry
point when the BFD is closed. The two entry points must work
together in order to produce the correct output file.
The details of how this works are inevitably dependent upon
the specific object file format. The a.out
_bfd_final_link routine is NAME(aout,final_link).
Before the linker calls the _bfd_final_link entry point,
it sets up some data structures for the function to use.
The input_bfds field of the bfd_link_info structure
will point to a list of all the input files included in the
link. These files are linked through the link_next field
of the bfd structure.
Each section in the output file will have a list of
link_order structures attached to the link_order_head
field (the link_order structure is defined in
bfdlink.h). These structures describe how to create the
contents of the output section in terms of the contents of
various input sections, fill constants, and, eventually, other
types of information. They also describe relocs that must be
created by the BFD backend, but do not correspond to any input
file; this is used to support -Ur, which builds constructors
while generating a relocateable object file.
The _bfd_final_link function should look through the
link_order structures attached to each section of the
output file. Each link_order structure should either be
handled specially, or it should be passed to the function
_bfd_default_link_order which will do the right thing
(_bfd_default_link_order is defined in linker.c).
For efficiency, a link_order of type
bfd_indirect_link_order whose associated section belongs
to a BFD of the same format as the output BFD must be handled
specially. This type of link_order describes part of an
output section in terms of a section belonging to one of the
input files. The _bfd_final_link function should read the
contents of the section and any associated relocs, apply the
relocs to the section contents, and write out the modified
section contents. If performing a relocateable link, the
relocs themselves must also be modified and written out.
The functions _bfd_relocate_contents and
_bfd_final_link_relocate provide some general support for
performing the actual relocations, notably overflow checking.
Their arguments include information about the symbol the
relocation is against and a reloc_howto_type argument
which describes the relocation to perform. These functions
are defined in reloc.c.
The a.out function which handles reading, relocating, and
writing section contents is aout_link_input_section. The
actual relocation is done in aout_link_input_section_std
and aout_link_input_section_ext.
The _bfd_final_link function must gather all the symbols
in the input files and write them out. It must also write out
all the symbols in the global hash table. This must be
controlled by the strip and discard fields of the
bfd_link_info structure.
The local symbols of the input files will not have been
entered into the linker hash table. The _bfd_final_link
routine must consider each input file and include the symbols
in the output file. It may be convenient to do this when
looking through the link_order structures, or it may be
done by stepping through the input_bfds list.
The _bfd_final_link routine must also traverse the global
hash table to gather all the externally visible symbols. It
is possible that most of the externally visible symbols may be
written out when considering the symbols of each input file,
but it is still necessary to traverse the hash table since the
linker script may have defined some symbols that are not in
any of the input files.
The strip field of the bfd_link_info structure
controls which symbols are written out. The possible values
are listed in bfdlink.h. If the value is strip_some,
then the keep_hash field of the bfd_link_info
structure is a hash table of symbols to keep; each symbol
should be looked up in this hash table, and only symbols which
are present should be included in the output file.
If the strip field of the bfd_link_info structure
permits local symbols to be written out, the discard field
is used to further controls which local symbols are included
in the output file. If the value is discard_l, then all
local symbols which begin with a certain prefix are discarded;
this is controlled by the bfd_is_local_label_name entry point.
The a.out backend handles symbols by calling
aout_link_write_symbols on each input BFD and then
traversing the global hash table with the function
aout_link_write_other_symbol. It builds a string table
while writing out the symbols, which is written to the output
file at the end of NAME(aout,final_link).
bfd_link_split_sectionSynopsis
boolean bfd_link_split_section(bfd *abfd, asection *sec);
Description
Return nonzero if sec should be split during a
reloceatable or final link.
#define bfd_link_split_section(abfd, sec) \
BFD_SEND (abfd, _bfd_link_split_section, (abfd, sec))
BFD provides a simple set of hash table functions. Routines are provided to initialize a hash table, to free a hash table, to look up a string in a hash table and optionally create an entry for it, and to traverse a hash table. There is currently no routine to delete an string from a hash table.
The basic hash table does not permit any data to be stored with a string. However, a hash table is designed to present a base class from which other types of hash tables may be derived. These derived types may store additional information with the string. Hash tables were implemented in this way, rather than simply providing a data pointer in a hash table entry, because they were designed for use by the linker back ends. The linker may create thousands of hash table entries, and the overhead of allocating private data and storing and following pointers becomes noticeable.
The basic hash table code is in hash.c.
To create a hash table, create an instance of a struct
bfd_hash_table (defined in bfd.h) and call
bfd_hash_table_init (if you know approximately how many
entries you will need, the function bfd_hash_table_init_n,
which takes a size argument, may be used).
bfd_hash_table_init returns false if some sort of
error occurs.
The function bfd_hash_table_init take as an argument a
function to use to create new entries. For a basic hash
table, use the function bfd_hash_newfunc. See section Deriving a new hash table type for why you would want to use a
different value for this argument.
bfd_hash_table_init will create an objalloc which will be
used to allocate new entries. You may allocate memory on this
objalloc using bfd_hash_allocate.
Use bfd_hash_table_free to free up all the memory that has
been allocated for a hash table. This will not free up the
struct bfd_hash_table itself, which you must provide.
The function bfd_hash_lookup is used both to look up a
string in the hash table and to create a new entry.
If the create argument is false, bfd_hash_lookup
will look up a string. If the string is found, it will
returns a pointer to a struct bfd_hash_entry. If the
string is not found in the table bfd_hash_lookup will
return NULL. You should not modify any of the fields in
the returns struct bfd_hash_entry.
If the create argument is true, the string will be
entered into the hash table if it is not already there.
Either way a pointer to a struct bfd_hash_entry will be
returned, either to the existing structure or to a newly
created one. In this case, a NULL return means that an
error occurred.
If the create argument is true, and a new entry is
created, the copy argument is used to decide whether to
copy the string onto the hash table objalloc or not. If
copy is passed as false, you must be careful not to
deallocate or modify the string as long as the hash table
exists.
The function bfd_hash_traverse may be used to traverse a
hash table, calling a function on each element. The traversal
is done in a random order.
bfd_hash_traverse takes as arguments a function and a
generic void * pointer. The function is called with a
hash table entry (a struct bfd_hash_entry *) and the
generic pointer passed to bfd_hash_traverse. The function
must return a boolean value, which indicates whether to
continue traversing the hash table. If the function returns
false, bfd_hash_traverse will stop the traversal and
return immediately.
Many uses of hash tables want to store additional information which each entry in the hash table. Some also find it convenient to store additional information with the hash table itself. This may be done using a derived hash table.
Since C is not an object oriented language, creating a derived hash table requires sticking together some boilerplate routines with a few differences specific to the type of hash table you want to create.
An example of a derived hash table is the linker hash table.
The structures for this are defined in bfdlink.h. The
functions are in linker.c.
You may also derive a hash table from an already derived hash table. For example, the a.out linker backend code uses a hash table derived from the linker hash table.
You must define a structure for an entry in the hash table, and a structure for the hash table itself.
The first field in the structure for an entry in the hash
table must be of the type used for an entry in the hash table
you are deriving from. If you are deriving from a basic hash
table this is struct bfd_hash_entry, which is defined in
bfd.h. The first field in the structure for the hash
table itself must be of the type of the hash table you are
deriving from itself. If you are deriving from a basic hash
table, this is struct bfd_hash_table.
For example, the linker hash table defines struct
bfd_link_hash_entry (in bfdlink.h). The first field,
root, is of type struct bfd_hash_entry. Similarly,
the first field in struct bfd_link_hash_table, table,
is of type struct bfd_hash_table.
You must write a routine which will create and initialize an
entry in the hash table. This routine is passed as the
function argument to bfd_hash_table_init.
In order to permit other hash tables to be derived from the hash table you are creating, this routine must be written in a standard way.
The first argument to the creation routine is a pointer to a
hash table entry. This may be NULL, in which case the
routine should allocate the right amount of space. Otherwise
the space has already been allocated by a hash table type
derived from this one.
After allocating space, the creation routine must call the creation routine of the hash table type it is derived from, passing in a pointer to the space it just allocated. This will initialize any fields used by the base hash table.
Finally the creation routine must initialize any local fields for the new hash table type.
Here is a boilerplate example of a creation routine. function_name is the name of the routine. entry_type is the type of an entry in the hash table you are creating. base_newfunc is the name of the creation routine of the hash table type your hash table is derived from.
struct bfd_hash_entry *
function_name (entry, table, string)
struct bfd_hash_entry *entry;
struct bfd_hash_table *table;
const char *string;
{
struct entry_type *ret = (entry_type *) entry;
/* Allocate the structure if it has not already been allocated by a
derived class. */
if (ret == (entry_type *) NULL)
{
ret = ((entry_type *)
bfd_hash_allocate (table, sizeof (entry_type)));
if (ret == (entry_type *) NULL)
return NULL;
}
/* Call the allocation method of the base class. */
ret = ((entry_type *)
base_newfunc ((struct bfd_hash_entry *) ret, table, string));
/* Initialize the local fields here. */
return (struct bfd_hash_entry *) ret;
}
Description
The creation routine for the linker hash table, which is in
linker.c, looks just like this example.
function_name is _bfd_link_hash_newfunc.
entry_type is struct bfd_link_hash_entry.
base_newfunc is bfd_hash_newfunc, the creation
routine for a basic hash table.
_bfd_link_hash_newfunc also initializes the local fields
in a linker hash table entry: type, written and
next.
You will want to write other routines for your new hash table, as well.
You will want an initialization routine which calls the
initialization routine of the hash table you are deriving from
and initializes any other local fields. For the linker hash
table, this is _bfd_link_hash_table_init in linker.c.
You will want a lookup routine which calls the lookup routine
of the hash table you are deriving from and casts the result.
The linker hash table uses bfd_link_hash_lookup in
linker.c (this actually takes an additional argument which
it uses to decide how to return the looked up value).
You may want a traversal routine. This should just call the
traversal routine of the hash table you are deriving from with
appropriate casts. The linker hash table uses
bfd_link_hash_traverse in linker.c.
These routines may simply be defined as macros. For example,
the a.out backend linker hash table, which is derived from the
linker hash table, uses macros for the lookup and traversal
routines. These are aout_link_hash_lookup and
aout_link_hash_traverse in aoutx.h.
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