bfd: coff
3.3 coff backends
=================
BFD supports a number of different flavours of coff format. The major
differences between formats are the sizes and alignments of fields in
structures on disk, and the occasional extra field.
Coff in all its varieties is implemented with a few common files and
a number of implementation specific files. For example, the i386 coff
format is implemented in the file 'coff-i386.c'. This file '#include's
'coff/i386.h' which defines the external structure of the coff format
for the i386, and 'coff/internal.h' which defines the internal
structure. 'coff-i386.c' also defines the relocations used by the i386
coff format 
Relocations.
3.3.1 Porting to a new version of coff
--------------------------------------
The recommended method is to select from the existing implementations
the version of coff which is most like the one you want to use. For
example, we'll say that i386 coff is the one you select, and that your
coff flavour is called foo. Copy 'i386coff.c' to 'foocoff.c', copy
'../include/coff/i386.h' to '../include/coff/foo.h', and add the lines
to 'targets.c' and 'Makefile.in' so that your new back end is used.
Alter the shapes of the structures in '../include/coff/foo.h' so that
they match what you need. You will probably also have to add '#ifdef's
to the code in 'coff/internal.h' and 'coffcode.h' if your version of
coff is too wild.
You can verify that your new BFD backend works quite simply by
building 'objdump' from the 'binutils' directory, and making sure that
its version of what's going on and your host system's idea (assuming it
has the pretty standard coff dump utility, usually called 'att-dump' or
just 'dump') are the same. Then clean up your code, and send what
you've done to Cygnus. Then your stuff will be in the next release, and
you won't have to keep integrating it.
3.3.2 How the coff backend works
--------------------------------
3.3.2.1 File layout
...................
The Coff backend is split into generic routines that are applicable to
any Coff target and routines that are specific to a particular target.
The target-specific routines are further split into ones which are
basically the same for all Coff targets except that they use the
external symbol format or use different values for certain constants.
The generic routines are in 'coffgen.c'. These routines work for any
Coff target. They use some hooks into the target specific code; the
hooks are in a 'bfd_coff_backend_data' structure, one of which exists
for each target.
The essentially similar target-specific routines are in 'coffcode.h'.
This header file includes executable C code. The various Coff targets
first include the appropriate Coff header file, make any special defines
that are needed, and then include 'coffcode.h'.
Some of the Coff targets then also have additional routines in the
target source file itself.
3.3.2.2 Coff long section names
...............................
In the standard Coff object format, section names are limited to the
eight bytes available in the 's_name' field of the 'SCNHDR' section
header structure. The format requires the field to be NUL-padded, but
not necessarily NUL-terminated, so the longest section names permitted
are a full eight characters.
The Microsoft PE variants of the Coff object file format add an
extension to support the use of long section names. This extension is
defined in section 4 of the Microsoft PE/COFF specification (rev 8.1).
If a section name is too long to fit into the section header's 's_name'
field, it is instead placed into the string table, and the 's_name'
field is filled with a slash ("/") followed by the ASCII decimal
representation of the offset of the full name relative to the string
table base.
Note that this implies that the extension can only be used in object
files, as executables do not contain a string table. The standard
specifies that long section names from objects emitted into executable
images are to be truncated.
However, as a GNU extension, BFD can generate executable images that
contain a string table and long section names. This would appear to be
technically valid, as the standard only says that Coff debugging
information is deprecated, not forbidden, and in practice it works,
although some tools that parse PE files expecting the MS standard format
may become confused; 'PEview' is one known example.
The functionality is supported in BFD by code implemented under the
control of the macro 'COFF_LONG_SECTION_NAMES'. If not defined, the
format does not support long section names in any way. If defined, it
is used to initialise a flag, '_bfd_coff_long_section_names', and a hook
function pointer, '_bfd_coff_set_long_section_names', in the Coff
backend data structure. The flag controls the generation of long
section names in output BFDs at runtime; if it is false, as it will be
by default when generating an executable image, long section names are
truncated; if true, the long section names extension is employed. The
hook points to a function that allows the value of the flag to be
altered at runtime, on formats that support long section names at all;
on other formats it points to a stub that returns an error indication.
With input BFDs, the flag is set according to whether any long
section names are detected while reading the section headers. For a
completely new BFD, the flag is set to the default for the target
format. This information can be used by a client of the BFD library
when deciding what output format to generate, and means that a BFD that
is opened for read and subsequently converted to a writeable BFD and
modified in-place will retain whatever format it had on input.
If 'COFF_LONG_SECTION_NAMES' is simply defined (blank), or is defined
to the value "1", then long section names are enabled by default; if it
is defined to the value zero, they are disabled by default (but still
accepted in input BFDs). The header 'coffcode.h' defines a macro,
'COFF_DEFAULT_LONG_SECTION_NAMES', which is used in the backends to
initialise the backend data structure fields appropriately; see the
comments for further detail.
3.3.2.3 Bit twiddling
.....................
Each flavour of coff supported in BFD has its own header file describing
the external layout of the structures. There is also an internal
description of the coff layout, in 'coff/internal.h'. A major function
of the coff backend is swapping the bytes and twiddling the bits to
translate the external form of the structures into the normal internal
form. This is all performed in the 'bfd_swap'_thing_direction routines.
Some elements are different sizes between different versions of coff; it
is the duty of the coff version specific include file to override the
definitions of various packing routines in 'coffcode.h'. E.g., the size
of line number entry in coff is sometimes 16 bits, and sometimes 32
bits. '#define'ing 'PUT_LNSZ_LNNO' and 'GET_LNSZ_LNNO' will select the
correct one. No doubt, some day someone will find a version of coff
which has a varying field size not catered to at the moment. To port
BFD, that person will have to add more '#defines'. Three of the bit
twiddling routines are exported to 'gdb'; 'coff_swap_aux_in',
'coff_swap_sym_in' and 'coff_swap_lineno_in'. 'GDB' reads the symbol
table on its own, but uses BFD to fix things up. More of the bit
twiddlers are exported for 'gas'; 'coff_swap_aux_out',
'coff_swap_sym_out', 'coff_swap_lineno_out', 'coff_swap_reloc_out',
'coff_swap_filehdr_out', 'coff_swap_aouthdr_out',
'coff_swap_scnhdr_out'. 'Gas' currently keeps track of all the symbol
table and reloc drudgery itself, thereby saving the internal BFD
overhead, but uses BFD to swap things on the way out, making cross ports
much safer. Doing so also allows BFD (and thus the linker) to use the
same header files as 'gas', which makes one avenue to disaster
disappear.
3.3.2.4 Symbol reading
......................
The simple canonical form for symbols used by BFD is not rich enough to
keep all the information available in a coff symbol table. The back end
gets around this problem by keeping the original symbol table around,
"behind the scenes".
When a symbol table is requested (through a call to
'bfd_canonicalize_symtab'), a request gets through to
'coff_get_normalized_symtab'. This reads the symbol table from the coff
file and swaps all the structures inside into the internal form. It
also fixes up all the pointers in the table (represented in the file by
offsets from the first symbol in the table) into physical pointers to
elements in the new internal table. This involves some work since the
meanings of fields change depending upon context: a field that is a
pointer to another structure in the symbol table at one moment may be
the size in bytes of a structure at the next. Another pass is made over
the table. All symbols which mark file names ('C_FILE' symbols) are
modified so that the internal string points to the value in the auxent
(the real filename) rather than the normal text associated with the
symbol ('".file"').
At this time the symbol names are moved around. Coff stores all
symbols less than nine characters long physically within the symbol
table; longer strings are kept at the end of the file in the string
table. This pass moves all strings into memory and replaces them with
pointers to the strings.
The symbol table is massaged once again, this time to create the
canonical table used by the BFD application. Each symbol is inspected
in turn, and a decision made (using the 'sclass' field) about the
various flags to set in the 'asymbol'. Symbols. The generated
canonical table shares strings with the hidden internal symbol table.
Any linenumbers are read from the coff file too, and attached to the
symbols which own the functions the linenumbers belong to.
3.3.2.5 Symbol writing
......................
Writing a symbol to a coff file which didn't come from a coff file will
lose any debugging information. The 'asymbol' structure remembers the
BFD from which the symbol was taken, and on output the back end makes
sure that the same destination target as source target is present.
When the symbols have come from a coff file then all the debugging
information is preserved.
Symbol tables are provided for writing to the back end in a vector of
pointers to pointers. This allows applications like the linker to
accumulate and output large symbol tables without having to do too much
byte copying.
This function runs through the provided symbol table and patches each
symbol marked as a file place holder ('C_FILE') to point to the next
file place holder in the list. It also marks each 'offset' field in the
list with the offset from the first symbol of the current symbol.
Another function of this procedure is to turn the canonical value
form of BFD into the form used by coff. Internally, BFD expects symbol
values to be offsets from a section base; so a symbol physically at
0x120, but in a section starting at 0x100, would have the value 0x20.
Coff expects symbols to contain their final value, so symbols have their
values changed at this point to reflect their sum with their owning
section. This transformation uses the 'output_section' field of the
'asymbol''s 'asection' Sections.
* 'coff_mangle_symbols'
This routine runs though the provided symbol table and uses the
offsets generated by the previous pass and the pointers generated when
the symbol table was read in to create the structured hierarchy required
by coff. It changes each pointer to a symbol into the index into the
symbol table of the asymbol.
* 'coff_write_symbols'
This routine runs through the symbol table and patches up the symbols
from their internal form into the coff way, calls the bit twiddlers, and
writes out the table to the file.
3.3.2.6 'coff_symbol_type'
..........................
*Description*
The hidden information for an 'asymbol' is described in a
'combined_entry_type':
typedef struct coff_ptr_struct
{
/* Remembers the offset from the first symbol in the file for
this symbol. Generated by coff_renumber_symbols. */
unsigned int offset;
/* Should the value of this symbol be renumbered. Used for
XCOFF C_BSTAT symbols. Set by coff_slurp_symbol_table. */
unsigned int fix_value : 1;
/* Should the tag field of this symbol be renumbered.
Created by coff_pointerize_aux. */
unsigned int fix_tag : 1;
/* Should the endidx field of this symbol be renumbered.
Created by coff_pointerize_aux. */
unsigned int fix_end : 1;
/* Should the x_csect.x_scnlen field be renumbered.
Created by coff_pointerize_aux. */
unsigned int fix_scnlen : 1;
/* Fix up an XCOFF C_BINCL/C_EINCL symbol. The value is the
index into the line number entries. Set by coff_slurp_symbol_table. */
unsigned int fix_line : 1;
/* The container for the symbol structure as read and translated
from the file. */
union
{
union internal_auxent auxent;
struct internal_syment syment;
} u;
/* Selector for the union above. */
bfd_boolean is_sym;
} combined_entry_type;
/* Each canonical asymbol really looks like this: */
typedef struct coff_symbol_struct
{
/* The actual symbol which the rest of BFD works with */
asymbol symbol;
/* A pointer to the hidden information for this symbol */
combined_entry_type *native;
/* A pointer to the linenumber information for this symbol */
struct lineno_cache_entry *lineno;
/* Have the line numbers been relocated yet ? */
bfd_boolean done_lineno;
} coff_symbol_type;
3.3.2.7 'bfd_coff_backend_data'
...............................
/* COFF symbol classifications. */
enum coff_symbol_classification
{
/* Global symbol. */
COFF_SYMBOL_GLOBAL,
/* Common symbol. */
COFF_SYMBOL_COMMON,
/* Undefined symbol. */
COFF_SYMBOL_UNDEFINED,
/* Local symbol. */
COFF_SYMBOL_LOCAL,
/* PE section symbol. */
COFF_SYMBOL_PE_SECTION
};
typedef asection * (*coff_gc_mark_hook_fn)
(asection *, struct bfd_link_info *, struct internal_reloc *,
struct coff_link_hash_entry *, struct internal_syment *);
Special entry points for gdb to swap in coff symbol table parts:
typedef struct
{
void (*_bfd_coff_swap_aux_in)
(bfd *, void *, int, int, int, int, void *);
void (*_bfd_coff_swap_sym_in)
(bfd *, void *, void *);
void (*_bfd_coff_swap_lineno_in)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_aux_out)
(bfd *, void *, int, int, int, int, void *);
unsigned int (*_bfd_coff_swap_sym_out)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_lineno_out)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_reloc_out)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_filehdr_out)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_aouthdr_out)
(bfd *, void *, void *);
unsigned int (*_bfd_coff_swap_scnhdr_out)
(bfd *, void *, void *);
unsigned int _bfd_filhsz;
unsigned int _bfd_aoutsz;
unsigned int _bfd_scnhsz;
unsigned int _bfd_symesz;
unsigned int _bfd_auxesz;
unsigned int _bfd_relsz;
unsigned int _bfd_linesz;
unsigned int _bfd_filnmlen;
bfd_boolean _bfd_coff_long_filenames;
bfd_boolean _bfd_coff_long_section_names;
bfd_boolean (*_bfd_coff_set_long_section_names)
(bfd *, int);
unsigned int _bfd_coff_default_section_alignment_power;
bfd_boolean _bfd_coff_force_symnames_in_strings;
unsigned int _bfd_coff_debug_string_prefix_length;
unsigned int _bfd_coff_max_nscns;
void (*_bfd_coff_swap_filehdr_in)
(bfd *, void *, void *);
void (*_bfd_coff_swap_aouthdr_in)
(bfd *, void *, void *);
void (*_bfd_coff_swap_scnhdr_in)
(bfd *, void *, void *);
void (*_bfd_coff_swap_reloc_in)
(bfd *abfd, void *, void *);
bfd_boolean (*_bfd_coff_bad_format_hook)
(bfd *, void *);
bfd_boolean (*_bfd_coff_set_arch_mach_hook)
(bfd *, void *);
void * (*_bfd_coff_mkobject_hook)
(bfd *, void *, void *);
bfd_boolean (*_bfd_styp_to_sec_flags_hook)
(bfd *, void *, const char *, asection *, flagword *);
void (*_bfd_set_alignment_hook)
(bfd *, asection *, void *);
bfd_boolean (*_bfd_coff_slurp_symbol_table)
(bfd *);
bfd_boolean (*_bfd_coff_symname_in_debug)
(bfd *, struct internal_syment *);
bfd_boolean (*_bfd_coff_pointerize_aux_hook)
(bfd *, combined_entry_type *, combined_entry_type *,
unsigned int, combined_entry_type *);
bfd_boolean (*_bfd_coff_print_aux)
(bfd *, FILE *, combined_entry_type *, combined_entry_type *,
combined_entry_type *, unsigned int);
void (*_bfd_coff_reloc16_extra_cases)
(bfd *, struct bfd_link_info *, struct bfd_link_order *, arelent *,
bfd_byte *, unsigned int *, unsigned int *);
int (*_bfd_coff_reloc16_estimate)
(bfd *, asection *, arelent *, unsigned int,
struct bfd_link_info *);
enum coff_symbol_classification (*_bfd_coff_classify_symbol)
(bfd *, struct internal_syment *);
bfd_boolean (*_bfd_coff_compute_section_file_positions)
(bfd *);
bfd_boolean (*_bfd_coff_start_final_link)
(bfd *, struct bfd_link_info *);
bfd_boolean (*_bfd_coff_relocate_section)
(bfd *, struct bfd_link_info *, bfd *, asection *, bfd_byte *,
struct internal_reloc *, struct internal_syment *, asection **);
reloc_howto_type *(*_bfd_coff_rtype_to_howto)
(bfd *, asection *, struct internal_reloc *,
struct coff_link_hash_entry *, struct internal_syment *, bfd_vma *);
bfd_boolean (*_bfd_coff_adjust_symndx)
(bfd *, struct bfd_link_info *, bfd *, asection *,
struct internal_reloc *, bfd_boolean *);
bfd_boolean (*_bfd_coff_link_add_one_symbol)
(struct bfd_link_info *, bfd *, const char *, flagword,
asection *, bfd_vma, const char *, bfd_boolean, bfd_boolean,
struct bfd_link_hash_entry **);
bfd_boolean (*_bfd_coff_link_output_has_begun)
(bfd *, struct coff_final_link_info *);
bfd_boolean (*_bfd_coff_final_link_postscript)
(bfd *, struct coff_final_link_info *);
bfd_boolean (*_bfd_coff_print_pdata)
(bfd *, void *);
} bfd_coff_backend_data;
#define coff_backend_info(abfd) \
((bfd_coff_backend_data *) (abfd)->xvec->backend_data)
#define bfd_coff_swap_aux_in(a,e,t,c,ind,num,i) \
((coff_backend_info (a)->_bfd_coff_swap_aux_in) (a,e,t,c,ind,num,i))
#define bfd_coff_swap_sym_in(a,e,i) \
((coff_backend_info (a)->_bfd_coff_swap_sym_in) (a,e,i))
#define bfd_coff_swap_lineno_in(a,e,i) \
((coff_backend_info ( a)->_bfd_coff_swap_lineno_in) (a,e,i))
#define bfd_coff_swap_reloc_out(abfd, i, o) \
((coff_backend_info (abfd)->_bfd_coff_swap_reloc_out) (abfd, i, o))
#define bfd_coff_swap_lineno_out(abfd, i, o) \
((coff_backend_info (abfd)->_bfd_coff_swap_lineno_out) (abfd, i, o))
#define bfd_coff_swap_aux_out(a,i,t,c,ind,num,o) \
((coff_backend_info (a)->_bfd_coff_swap_aux_out) (a,i,t,c,ind,num,o))
#define bfd_coff_swap_sym_out(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_sym_out) (abfd, i, o))
#define bfd_coff_swap_scnhdr_out(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_scnhdr_out) (abfd, i, o))
#define bfd_coff_swap_filehdr_out(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_filehdr_out) (abfd, i, o))
#define bfd_coff_swap_aouthdr_out(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_aouthdr_out) (abfd, i, o))
#define bfd_coff_filhsz(abfd) (coff_backend_info (abfd)->_bfd_filhsz)
#define bfd_coff_aoutsz(abfd) (coff_backend_info (abfd)->_bfd_aoutsz)
#define bfd_coff_scnhsz(abfd) (coff_backend_info (abfd)->_bfd_scnhsz)
#define bfd_coff_symesz(abfd) (coff_backend_info (abfd)->_bfd_symesz)
#define bfd_coff_auxesz(abfd) (coff_backend_info (abfd)->_bfd_auxesz)
#define bfd_coff_relsz(abfd) (coff_backend_info (abfd)->_bfd_relsz)
#define bfd_coff_linesz(abfd) (coff_backend_info (abfd)->_bfd_linesz)
#define bfd_coff_filnmlen(abfd) (coff_backend_info (abfd)->_bfd_filnmlen)
#define bfd_coff_long_filenames(abfd) \
(coff_backend_info (abfd)->_bfd_coff_long_filenames)
#define bfd_coff_long_section_names(abfd) \
(coff_backend_info (abfd)->_bfd_coff_long_section_names)
#define bfd_coff_set_long_section_names(abfd, enable) \
((coff_backend_info (abfd)->_bfd_coff_set_long_section_names) (abfd, enable))
#define bfd_coff_default_section_alignment_power(abfd) \
(coff_backend_info (abfd)->_bfd_coff_default_section_alignment_power)
#define bfd_coff_max_nscns(abfd) \
(coff_backend_info (abfd)->_bfd_coff_max_nscns)
#define bfd_coff_swap_filehdr_in(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_filehdr_in) (abfd, i, o))
#define bfd_coff_swap_aouthdr_in(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_aouthdr_in) (abfd, i, o))
#define bfd_coff_swap_scnhdr_in(abfd, i,o) \
((coff_backend_info (abfd)->_bfd_coff_swap_scnhdr_in) (abfd, i, o))
#define bfd_coff_swap_reloc_in(abfd, i, o) \
((coff_backend_info (abfd)->_bfd_coff_swap_reloc_in) (abfd, i, o))
#define bfd_coff_bad_format_hook(abfd, filehdr) \
((coff_backend_info (abfd)->_bfd_coff_bad_format_hook) (abfd, filehdr))
#define bfd_coff_set_arch_mach_hook(abfd, filehdr)\
((coff_backend_info (abfd)->_bfd_coff_set_arch_mach_hook) (abfd, filehdr))
#define bfd_coff_mkobject_hook(abfd, filehdr, aouthdr)\
((coff_backend_info (abfd)->_bfd_coff_mkobject_hook)\
(abfd, filehdr, aouthdr))
#define bfd_coff_styp_to_sec_flags_hook(abfd, scnhdr, name, section, flags_ptr)\
((coff_backend_info (abfd)->_bfd_styp_to_sec_flags_hook)\
(abfd, scnhdr, name, section, flags_ptr))
#define bfd_coff_set_alignment_hook(abfd, sec, scnhdr)\
((coff_backend_info (abfd)->_bfd_set_alignment_hook) (abfd, sec, scnhdr))
#define bfd_coff_slurp_symbol_table(abfd)\
((coff_backend_info (abfd)->_bfd_coff_slurp_symbol_table) (abfd))
#define bfd_coff_symname_in_debug(abfd, sym)\
((coff_backend_info (abfd)->_bfd_coff_symname_in_debug) (abfd, sym))
#define bfd_coff_force_symnames_in_strings(abfd)\
(coff_backend_info (abfd)->_bfd_coff_force_symnames_in_strings)
#define bfd_coff_debug_string_prefix_length(abfd)\
(coff_backend_info (abfd)->_bfd_coff_debug_string_prefix_length)
#define bfd_coff_print_aux(abfd, file, base, symbol, aux, indaux)\
((coff_backend_info (abfd)->_bfd_coff_print_aux)\
(abfd, file, base, symbol, aux, indaux))
#define bfd_coff_reloc16_extra_cases(abfd, link_info, link_order,\
reloc, data, src_ptr, dst_ptr)\
((coff_backend_info (abfd)->_bfd_coff_reloc16_extra_cases)\
(abfd, link_info, link_order, reloc, data, src_ptr, dst_ptr))
#define bfd_coff_reloc16_estimate(abfd, section, reloc, shrink, link_info)\
((coff_backend_info (abfd)->_bfd_coff_reloc16_estimate)\
(abfd, section, reloc, shrink, link_info))
#define bfd_coff_classify_symbol(abfd, sym)\
((coff_backend_info (abfd)->_bfd_coff_classify_symbol)\
(abfd, sym))
#define bfd_coff_compute_section_file_positions(abfd)\
((coff_backend_info (abfd)->_bfd_coff_compute_section_file_positions)\
(abfd))
#define bfd_coff_start_final_link(obfd, info)\
((coff_backend_info (obfd)->_bfd_coff_start_final_link)\
(obfd, info))
#define bfd_coff_relocate_section(obfd,info,ibfd,o,con,rel,isyms,secs)\
((coff_backend_info (ibfd)->_bfd_coff_relocate_section)\
(obfd, info, ibfd, o, con, rel, isyms, secs))
#define bfd_coff_rtype_to_howto(abfd, sec, rel, h, sym, addendp)\
((coff_backend_info (abfd)->_bfd_coff_rtype_to_howto)\
(abfd, sec, rel, h, sym, addendp))
#define bfd_coff_adjust_symndx(obfd, info, ibfd, sec, rel, adjustedp)\
((coff_backend_info (abfd)->_bfd_coff_adjust_symndx)\
(obfd, info, ibfd, sec, rel, adjustedp))
#define bfd_coff_link_add_one_symbol(info, abfd, name, flags, section,\
value, string, cp, coll, hashp)\
((coff_backend_info (abfd)->_bfd_coff_link_add_one_symbol)\
(info, abfd, name, flags, section, value, string, cp, coll, hashp))
#define bfd_coff_link_output_has_begun(a,p) \
((coff_backend_info (a)->_bfd_coff_link_output_has_begun) (a, p))
#define bfd_coff_final_link_postscript(a,p) \
((coff_backend_info (a)->_bfd_coff_final_link_postscript) (a, p))
#define bfd_coff_have_print_pdata(a) \
(coff_backend_info (a)->_bfd_coff_print_pdata)
#define bfd_coff_print_pdata(a,p) \
((coff_backend_info (a)->_bfd_coff_print_pdata) (a, p))
/* Macro: Returns true if the bfd is a PE executable as opposed to a
PE object file. */
#define bfd_pei_p(abfd) \
(CONST_STRNEQ ((abfd)->xvec->name, "pei-"))
3.3.2.8 Writing relocations
...........................
To write relocations, the back end steps though the canonical relocation
table and create an 'internal_reloc'. The symbol index to use is
removed from the 'offset' field in the symbol table supplied. The
address comes directly from the sum of the section base address and the
relocation offset; the type is dug directly from the howto field. Then
the 'internal_reloc' is swapped into the shape of an 'external_reloc'
and written out to disk.
3.3.2.9 Reading linenumbers
...........................
Creating the linenumber table is done by reading in the entire coff
linenumber table, and creating another table for internal use.
A coff linenumber table is structured so that each function is marked
as having a line number of 0. Each line within the function is an
offset from the first line in the function. The base of the line number
information for the table is stored in the symbol associated with the
function.
Note: The PE format uses line number 0 for a flag indicating a new
source file.
The information is copied from the external to the internal table,
and each symbol which marks a function is marked by pointing its...
How does this work ?
3.3.2.10 Reading relocations
............................
Coff relocations are easily transformed into the internal BFD form
('arelent').
Reading a coff relocation table is done in the following stages:
* Read the entire coff relocation table into memory.
* Process each relocation in turn; first swap it from the external to
the internal form.
* Turn the symbol referenced in the relocation's symbol index into a
pointer into the canonical symbol table. This table is the same as
the one returned by a call to 'bfd_canonicalize_symtab'. The back
end will call that routine and save the result if a
canonicalization hasn't been done.
* The reloc index is turned into a pointer to a howto structure, in a
back end specific way. For instance, the 386 uses the 'r_type' to
directly produce an index into a howto table vector.
Info Catalog
bfd: aout
bfd: BFD back ends
bfd: elf