typedef bfd
bfd_printable_name
bfd_scan_arch
bfd_arch_list
bfd_arch_get_compatible
bfd_default_arch_struct
bfd_set_arch_info
bfd_default_set_arch_mach
bfd_get_arch
bfd_get_mach
bfd_arch_bits_per_byte
bfd_arch_bits_per_address
bfd_default_compatible
bfd_default_scan
bfd_get_arch_info
bfd_lookup_arch
bfd_printable_arch_mach
BFD is a package which allows applications to use the same routines to operate on object files whatever the object file format. A new object file format can be supported simply by creating a new BFD back end and adding it to the library.
BFD is split into two parts: the front end, and the back ends (one for each object file format).
One spur behind BFD was the desire, on the part of the GNU 960 team at Intel Oregon, for interoperability of applications on their COFF and b.out file formats. Cygnus was providing GNU support for the team, and was contracted to provide the required functionality.
The name came from a conversation David Wallace was having with Richard Stallman about the library: RMS said that it would be quite hard--David said "BFD". Stallman was right, but the name stuck.
At the same time, Ready Systems wanted much the same thing, but for different object file formats: IEEE-695, Oasys, Srecords, a.out and 68k coff.
BFD was first implemented by members of Cygnus Support; Steve
Chamberlain (sac@cygnus.com), John Gilmore
(gnu@cygnus.com), K. Richard Pixley (rich@cygnus.com)
and David Henkel-Wallace (gumby@cygnus.com).
To use the library, include `bfd.h' and link with `libbfd.a'.
BFD provides a common interface to the parts of an object file for a calling application.
When an application sucessfully opens a target file (object, archive, or
whatever), a pointer to an internal structure is returned. This pointer
points to a structure called bfd, described in
`bfd.h'. Our convention is to call this pointer a BFD, and
instances of it within code abfd. All operations on
the target object file are applied as methods to the BFD. The mapping is
defined within bfd.h in a set of macros, all beginning
with `bfd_' to reduce namespace pollution.
For example, this sequence does what you would probably expect:
return the number of sections in an object file attached to a BFD
abfd.
#include "bfd.h"
unsigned int number_of_sections(abfd)
bfd *abfd;
{
return bfd_count_sections(abfd);
}
The abstraction used within BFD is that an object file has:
Also, BFDs opened for archives have the additional attribute of an index and contain subordinate BFDs. This approach is fine for a.out and coff, but loses efficiency when applied to formats such as S-records and IEEE-695.
When an object file is opened, BFD subroutines automatically determine the format of the input object file. They then build a descriptor in memory with pointers to routines that will be used to access elements of the object file's data structures.
As different information from the the object files is required, BFD reads from different sections of the file and processes them. For example, a very common operation for the linker is processing symbol tables. Each BFD back end provides a routine for converting between the object file's representation of symbols and an internal canonical format. When the linker asks for the symbol table of an object file, it calls through a memory pointer to the routine from the relevant BFD back end which reads and converts the table into a canonical form. The linker then operates upon the canonical form. When the link is finished and the linker writes the output file's symbol table, another BFD back end routine is called to take the newly created symbol table and convert it into the chosen output format.
Information can be lost during output. The output formats
supported by BFD do not provide identical facilities, and
information which can be described in one form has nowhere to go in
another format. One example of this is alignment information in
b.out. There is nowhere in an a.out format file to store
alignment information on the contained data, so when a file is linked
from b.out and an a.out image is produced, alignment
information will not propagate to the output file. (The linker will
still use the alignment information internally, so the link is performed
correctly).
Another example is COFF section names. COFF files may contain an
unlimited number of sections, each one with a textual section name. If
the target of the link is a format which does not have many sections (e.g.,
a.out) or has sections without names (e.g., the Oasys format), the
link cannot be done simply. You can circumvent this problem by
describing the desired input-to-output section mapping with the linker command
language.
Information can be lost during canonicalization. The BFD internal canonical form of the external formats is not exhaustive; there are structures in input formats for which there is no direct representation internally. This means that the BFD back ends cannot maintain all possible data richness through the transformation between external to internal and back to external formats.
This limitation is only a problem when an application reads one
format and writes another. Each BFD back end is responsible for
maintaining as much data as possible, and the internal BFD
canonical form has structures which are opaque to the BFD core,
and exported only to the back ends. When a file is read in one format,
the canonical form is generated for BFD and the application. At the
same time, the back end saves away any information which may otherwise
be lost. If the data is then written back in the same format, the back
end routine will be able to use the canonical form provided by the
BFD core as well as the information it prepared earlier. Since
there is a great deal of commonality between back ends,
there is no information lost when
linking or copying big endian COFF to little endian COFF, or a.out to
b.out. When a mixture of formats is linked, the information is
only lost from the files whose format differs from the destination.
The greatest potential for loss of information occurs when there is the least overlap between the information provided by the source format, that stored by the canonical format, and that needed by the destination format. A brief description of the canonical form may help you understand which kinds of data you can count on preserving across conversions.
ZMAGIC
file would have both the demand pageable bit and the write protected
text bit set. The byte order of the target is stored on a per-file
basis, so that big- and little-endian object files may be used with one
another.
ld can
operate on a collection of symbols of wildly different formats without
problems.
Normal global and simple local symbols are maintained on output, so an
output file (no matter its format) will retain symbols pointing to
functions and to global, static, and common variables. Some symbol
information is not worth retaining; in a.out, type information is
stored in the symbol table as long symbol names. This information would
be useless to most COFF debuggers; the linker has command line switches
to allow users to throw it away.
There is one word of type information within the symbol, so if the
format supports symbol type information within symbols (for example, COFF,
IEEE, Oasys) and the type is simple enough to fit within one word
(nearly everything but aggregates), the information will be preserved.
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.