This is Info file bfd.info, produced by Makeinfo-1.55 from the input file ./bfd.texinfo. START-INFO-DIR-ENTRY * Bfd:: The Binary File Descriptor library. END-INFO-DIR-ENTRY This file documents the BFD library. Copyright (C) 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, subject to the terms of the GNU General Public License, which includes the provision that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions.  File: bfd.info, Node: coff, Next: elf, Prev: aout, Up: BFD back end coff backends ============= BFD supports a number of different flavours of coff format. The major difference between formats are the sizes and alignments of fields in structures on disk, and the occasional extra field. Coff in all its varieties is implimented with a few common files and a number of implementation specific files. For example, The 88k bcs coff format is implemented in the file `coff-m88k.c'. This file `#include's `coff/m88k.h' which defines the external structure of the coff format for the 88k, and `coff/internal.h' which defines the internal structure. `coff-m88k.c' also defines the relocations used by the 88k format *Note Relocations::. The Intel i960 processor version of coff is implemented in `coff-i960.c'. This file has the same structure as `coff-m88k.c', except that it includes `coff/i960.h' rather than `coff-m88k.h'. Porting To A New Version of Coff -------------------------------- The recommended method is to select from the existing implimentations the version of coff which is most like the one you want to use, for our purposes, we'll say that i386 coff is the one you select, and that your coff flavour is called foo. Copy the `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 at your host systems 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. How The Coff Backend Works -------------------------- 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 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. For example, `coff-i960.c' includes `coff/internal.h' and `coff/i960.h'. It then defines a few constants, such as `I960', and includes `coffcode.h'. Since the i960 has complex relocation types, `coff-i960.c' also includes some code to manipulate the i960 relocs. This code is not in `coffcode.h' because it would not be used by any other target. Bit Twiddling ............. Each flavour of coff supported in BFD has its own header file descibing 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'. Eg 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 for 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_linno_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. This also allows BFD (and thus the linker) to use the same header files as `gas', which makes one avenue to disaster disappear. 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 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 changes 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 in 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' *Note 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. 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 was born, 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. Note that this transformation uses the `output_section' field of the `asymbol''s `asection' *Note 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 hierachy required by coff. It changes each pointer to a symbol to an index into the symbol table of the symbol being referenced. * 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 tabel to the file. `coff_symbol_type' .................. *Description* The hidden information for an asymbol is described in a coff_ptr_struct, which is typedefed to 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 tag field of this symbol be renumbered. Created by coff_pointerize_aux. */ char fix_tag; /* Should the endidx field of this symbol be renumbered. Created by coff_pointerize_aux. */ char fix_end; /* 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 ? */ boolean done_lineno; } coff_symbol_type; `bfd_coff_backend_data' ....................... Special entry points for gdb to swap in coff symbol table parts typedef struct { void (*_bfd_coff_swap_aux_in) PARAMS (( bfd *abfd , PTR ext, int type, int class , PTR in)); void (*_bfd_coff_swap_sym_in) PARAMS (( bfd *abfd , PTR ext, PTR in)); void (*_bfd_coff_swap_lineno_in) PARAMS (( bfd *abfd, PTR ext, PTR in)); Special entry points for gas to swap coff parts unsigned int (*_bfd_coff_swap_aux_out) PARAMS (( bfd *abfd, PTR in, int type, int class, PTR ext)); unsigned int (*_bfd_coff_swap_sym_out) PARAMS (( bfd *abfd, PTR in, PTR ext)); unsigned int (*_bfd_coff_swap_lineno_out) PARAMS (( bfd *abfd, PTR in, PTR ext)); unsigned int (*_bfd_coff_swap_reloc_out) PARAMS (( bfd *abfd, PTR src, PTR dst)); unsigned int (*_bfd_coff_swap_filehdr_out) PARAMS (( bfd *abfd, PTR in, PTR out)); unsigned int (*_bfd_coff_swap_aouthdr_out) PARAMS (( bfd *abfd, PTR in, PTR out)); unsigned int (*_bfd_coff_swap_scnhdr_out) PARAMS (( bfd *abfd, PTR in, PTR out)); Special entry points for generic COFF routines to call target dependent COFF routines unsigned int _bfd_filhsz; unsigned int _bfd_aoutsz; unsigned int _bfd_scnhsz; unsigned int _bfd_symesz; unsigned int _bfd_auxesz; unsigned int _bfd_linesz; boolean _bfd_coff_long_filenames; void (*_bfd_coff_swap_filehdr_in) PARAMS (( bfd *abfd, PTR ext, PTR in)); void (*_bfd_coff_swap_aouthdr_in) PARAMS (( bfd *abfd, PTR ext, PTR in)); void (*_bfd_coff_swap_scnhdr_in) PARAMS (( bfd *abfd, PTR ext, PTR in)); boolean (*_bfd_coff_bad_format_hook) PARAMS (( bfd *abfd, PTR internal_filehdr)); boolean (*_bfd_coff_set_arch_mach_hook) PARAMS (( bfd *abfd, PTR internal_filehdr)); PTR (*_bfd_coff_mkobject_hook) PARAMS (( bfd *abfd, PTR internal_filehdr, PTR internal_aouthdr)); flagword (*_bfd_styp_to_sec_flags_hook) PARAMS (( bfd *abfd, PTR internal_scnhdr)); asection *(*_bfd_make_section_hook) PARAMS (( bfd *abfd, char *name)); void (*_bfd_set_alignment_hook) PARAMS (( bfd *abfd, asection *sec, PTR internal_scnhdr)); boolean (*_bfd_coff_slurp_symbol_table) PARAMS (( bfd *abfd)); boolean (*_bfd_coff_symname_in_debug) PARAMS (( bfd *abfd, struct internal_syment *sym)); void (*_bfd_coff_reloc16_extra_cases) PARAMS (( bfd *abfd, struct bfd_seclet *seclet, arelent *reloc, bfd_byte *data, unsigned int *src_ptr, unsigned int *dst_ptr)); int (*_bfd_coff_reloc16_estimate) PARAMS (( asection *input_section, asymbol **symbols, arelent *r, unsigned int shrink)); } 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,i) \ ((coff_backend_info (a)->_bfd_coff_swap_aux_in) (a,e,t,c,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(abfd, i, t,c,o) \ ((coff_backend_info (abfd)->_bfd_coff_swap_aux_out) (abfd, i,t,c, 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_linesz(abfd) (coff_backend_info (abfd)->_bfd_linesz) #define bfd_coff_long_filenames(abfd) (coff_backend_info (abfd)->_bfd_coff_long_filenames) #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_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)\ ((coff_backend_info (abfd)->_bfd_styp_to_sec_flags_hook) (abfd, scnhdr)) #define bfd_coff_make_section_hook(abfd, name)\ ((coff_backend_info (abfd)->_bfd_make_section_hook) (abfd, name)) #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_reloc16_extra_cases(abfd, seclet, reloc, data, src_ptr, dst_ptr)\ ((coff_backend_info (abfd)->_bfd_coff_reloc16_extra_cases)\ (abfd, seclet, reloc, data, src_ptr, dst_ptr)) #define bfd_coff_reloc16_estimate(abfd, section, symbols, reloc, shrink)\ ((coff_backend_info (abfd)->_bfd_coff_reloc16_estimate)\ (section, symbols, reloc, shrink)) Writing Relocations ................... To write relocations, all the back end does is step 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 and 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. 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 line number 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. 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 ? Reading Relocations ................... Coff relocations are easily transformed into the internal BFD form (`arelent'). Reading a coff relocation table is done in the following stages: * The entire coff relocation table is read into memory. * Each relocation is processed in turn, first it is swapped from the external to the internal form. * The symbol referenced in the relocation's symbol index is turned intoa pointer into the canonical symbol table. Note that this table is the same as the one returned by a call to `bfd_canonicalize_symtab'. The back end will call the 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 and 960 use the `r_type' to directly produce an index into a howto table vector; the 88k subtracts a number from the `r_type' field and creates an addend field.  File: bfd.info, Node: elf, Prev: coff, Up: BFD back end ELF backends ============ BFD support for ELF formats is being worked on. Currently, the best supported back ends are for sparc and i386 (running svr4 or Solaris 2). Documentation of the internals of the support code still needs to be written. The code is changing quickly enough that we haven't bothered yet. `bfd_elf_find_section' ...................... *Synopsis* struct elf_internal_shdr *bfd_elf_find_section (bfd *abfd, char *name); *Description* Helper functions for GDB to locate the string tables. Since BFD hides string tables from callers, GDB needs to use an internal hook to find them. Sun's .stabstr, in particular, isn't even pointed to by the .stab section, so ordinary mechanisms wouldn't work to find it, even if we had some.  File: bfd.info, Node: Index, Prev: BFD back end, Up: Top Index ***** * Menu: * aout__machine_type: aout. * aout__mkobject: aout. * aout__new_section_hook: aout. * aout__set_arch_mach: aout. * aout__some_aout_object_p: aout. * aout__swap_exec_header_in: aout. * aout__swap_exec_header_out: aout. * BFD: Overview. * BFD canonical format: Canonical format. * bfd_alloc_by_size_t: Opening and Closing. * bfd_arch_bits_per_address: Architectures. * bfd_arch_bits_per_byte: Architectures. * bfd_arch_get_compatible: Architectures. * bfd_arch_init: Architectures. * bfd_arch_linkin: Architectures. * bfd_cache_close: File Caching. * bfd_cache_lookup: File Caching. * bfd_cache_lookup_worker: File Caching. * BFD_CACHE_MAX_OPEN macro: File Caching. * bfd_canonicalize_reloc: BFD front end. * bfd_canonicalize_symtab: symbol handling functions. * bfd_check_format: Formats. * bfd_check_init: Initialization. * bfd_close: Opening and Closing. * bfd_close_all_done: Opening and Closing. * bfd_coff_backend_data: coff. * bfd_constructor_entry: Constructors. * bfd_core_file_failing_command: Core Files. * bfd_core_file_failing_signal: Core Files. * bfd_create: Opening and Closing. * bfd_decode_symclass: symbol handling functions. * bfd_default_arch_struct: Architectures. * bfd_default_compatible: Architectures. * bfd_default_reloc_type_lookup: howto manager. * bfd_default_scan: Architectures. * bfd_default_set_arch_mach: Architectures. * bfd_elf_find_section: elf. * bfd_fdopenr: Opening and Closing. * bfd_find_target: bfd_target. * bfd_format_string: Formats. * bfd_generic_get_relocated_section_contents: howto manager. * bfd_generic_relax_section: howto manager. * bfd_get_arch: Architectures. * bfd_get_arch_info: Architectures. * bfd_get_elt_at_index: Archives. * bfd_get_mach: Architectures. * bfd_get_next_mapent: Archives. * bfd_get_reloc_upper_bound: BFD front end. * bfd_get_section_by_name: section prototypes. * bfd_get_section_contents: section prototypes. * bfd_get_size: Internal. * bfd_h_get_size: Internal. * bfd_h_put_size: Internal. * bfd_init: Initialization. * bfd_last_cache: File Caching. * bfd_log2: Internal. * bfd_lookup_arch: Architectures. * bfd_make_debug_symbol: symbol handling functions. * bfd_make_empty_symbol: symbol handling functions. * bfd_make_section: section prototypes. * bfd_make_section_anyway: section prototypes. * bfd_make_section_old_way: section prototypes. * bfd_map_over_sections: section prototypes. * bfd_openr: Opening and Closing. * bfd_openr_next_archived_file: Archives. * bfd_openw: Opening and Closing. * bfd_open_file: File Caching. * bfd_perform_relocation: typedef arelent. * bfd_printable_arch_mach: Architectures. * bfd_printable_name: Architectures. * bfd_print_symbol_vandf: symbol handling functions. * bfd_put_size: Internal. * bfd_reloc_code_type: howto manager. * bfd_scan_arch: Architectures. * bfd_scan_vma: BFD front end. * bfd_set_archive_head: Archives. * bfd_set_arch_info: Architectures. * bfd_set_file_flags: BFD front end. * bfd_set_format: Formats. * bfd_set_reloc: BFD front end. * bfd_set_section_contents: section prototypes. * bfd_set_section_flags: section prototypes. * bfd_set_section_size: section prototypes. * bfd_set_start_address: BFD front end. * bfd_set_symtab: symbol handling functions. * bfd_symbol_info: symbol handling functions. * bfd_target_list: bfd_target. * bfd_write_bigendian_4byte_int: Internal. * bfd_xmalloc: Internal. * bfd_xmalloc_by_size_t: Internal. * coff_symbol_type: coff. * core_file_matches_executable_p: Core Files. * get_symtab_upper_bound: symbol handling functions. * internal object-file format: Canonical format. * reloc_chain: typedef arelent. * stuff: BFD front end. * The bfd_get_gp_size function: BFD front end. * The bfd_get_mtime function: BFD front end. * The bfd_get_size function: BFD front end. * The bfd_set_gp_size function: BFD front end. * the HOWTO macro: typedef arelent. * what is it?: Overview. .