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diff --git a/bfd/doc/coffcode.texi b/bfd/doc/coffcode.texi new file mode 100644 index 0000000000..e487d84701 --- /dev/null +++ b/bfd/doc/coffcode.texi @@ -0,0 +1,685 @@ +@section 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 88k bcs coff format is implemented in the file +@file{coff-m88k.c}. This file @code{#include}s +@file{coff/m88k.h} which defines the external structure of the +coff format for the 88k, and @file{coff/internal.h} which +defines the internal structure. @file{coff-m88k.c} also +defines the relocations used by the 88k format +@xref{Relocations}. + +The Intel i960 processor version of coff is implemented in +@file{coff-i960.c}. This file has the same structure as +@file{coff-m88k.c}, except that it includes @file{coff/i960.h} +rather than @file{coff-m88k.h}. + +@subsection 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 @file{i386coff.c} to @file{foocoff.c}, copy +@file{../include/coff/i386.h} to @file{../include/coff/foo.h}, +and add the lines to @file{targets.c} and @file{Makefile.in} +so that your new back end is used. Alter the shapes of the +structures in @file{../include/coff/foo.h} so that they match +what you need. You will probably also have to add +@code{#ifdef}s to the code in @file{coff/internal.h} and +@file{coffcode.h} if your version of coff is too wild. + +You can verify that your new BFD backend works quite simply by +building @file{objdump} from the @file{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 @code{att-dump} or just +@code{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. + +@subsection How the coff backend works + + +@subsubsection 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 @file{coffgen.c}. These routines +work for any Coff target. They use some hooks into the target +specific code; the hooks are in a @code{bfd_coff_backend_data} +structure, one of which exists for each target. + +The essentially similar target-specific routines are in +@file{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 @file{coffcode.h}. + +Some of the Coff targets then also have additional routines in +the target source file itself. + +For example, @file{coff-i960.c} includes +@file{coff/internal.h} and @file{coff/i960.h}. It then +defines a few constants, such as @code{I960}, and includes +@file{coffcode.h}. Since the i960 has complex relocation +types, @file{coff-i960.c} also includes some code to +manipulate the i960 relocs. This code is not in +@file{coffcode.h} because it would not be used by any other +target. + +@subsubsection Coff long section names +In the standard Coff object format, section names are limited to +the eight bytes available in the @code{s_name} field of the +@code{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 @code{s_name} field, it is instead +placed into the string table, and the @code{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; @file{PEview} is +one known example. + +The functionality is supported in BFD by code implemented under +the control of the macro @code{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, +@code{_bfd_coff_long_section_names}, and a hook function pointer, +@code{_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 @code{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 @file{coffcode.h} +defines a macro, @code{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. + +@subsubsection 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 +@file{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 +@code{bfd_swap}_@i{thing}_@i{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 +@file{coffcode.h}. E.g., the size of line number entry in coff is +sometimes 16 bits, and sometimes 32 bits. @code{#define}ing +@code{PUT_LNSZ_LNNO} and @code{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 @code{#defines}. +Three of the bit twiddling routines are exported to +@code{gdb}; @code{coff_swap_aux_in}, @code{coff_swap_sym_in} +and @code{coff_swap_lineno_in}. @code{GDB} reads the symbol +table on its own, but uses BFD to fix things up. More of the +bit twiddlers are exported for @code{gas}; +@code{coff_swap_aux_out}, @code{coff_swap_sym_out}, +@code{coff_swap_lineno_out}, @code{coff_swap_reloc_out}, +@code{coff_swap_filehdr_out}, @code{coff_swap_aouthdr_out}, +@code{coff_swap_scnhdr_out}. @code{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 @code{gas}, which makes one avenue to disaster disappear. + +@subsubsection 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 +@code{bfd_canonicalize_symtab}), a request gets through to +@code{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 +(@code{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 +(@code{".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 +@code{sclass} field) about the various flags to set in the +@code{asymbol}. @xref{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. + +@subsubsection Symbol writing +Writing a symbol to a coff file which didn't come from a coff +file will lose any debugging information. The @code{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 +(@code{C_FILE}) to point to the next file place holder in the +list. It also marks each @code{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 +@code{output_section} field of the @code{asymbol}'s +@code{asection} @xref{Sections}. + +@itemize @bullet + +@item +@code{coff_mangle_symbols} +@end itemize +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. + +@itemize @bullet + +@item +@code{coff_write_symbols} +@end itemize +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. + +@findex coff_symbol_type +@subsubsection @code{coff_symbol_type} +@strong{Description}@* +The hidden information for an @code{asymbol} is described in a +@code{combined_entry_type}: + + +@example + +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; +@} 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; +@end example +@findex bfd_coff_backend_data +@subsubsection @code{bfd_coff_backend_data} + +@example +/* 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 +@}; + +@end example +Special entry points for gdb to swap in coff symbol table parts: +@example +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; + + 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_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-")) +@end example +@subsubsection Writing relocations +To write relocations, the back end steps though the +canonical relocation table and create an +@code{internal_reloc}. The symbol index to use is removed from +the @code{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 @code{internal_reloc} is +swapped into the shape of an @code{external_reloc} and written +out to disk. + +@subsubsection 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 ? + +@subsubsection Reading relocations +Coff relocations are easily transformed into the internal BFD form +(@code{arelent}). + +Reading a coff relocation table is done in the following stages: + +@itemize @bullet + +@item +Read the entire coff relocation table into memory. + +@item +Process each relocation in turn; first swap it from the +external to the internal form. + +@item +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 +@code{bfd_canonicalize_symtab}. The back end will call that +routine and save the result if a canonicalization hasn't been done. + +@item +The reloc index is turned into a pointer to a howto +structure, in a back end specific way. For instance, the 386 +and 960 use the @code{r_type} to directly produce an index +into a howto table vector; the 88k subtracts a number from the +@code{r_type} field and creates an addend field. +@end itemize + |