/* Generic symbol-table support for the BFD library. Copyright (C) 1990-1991 Free Software Foundation, Inc. Written by Cygnus Support. This file is part of BFD, the Binary File Descriptor library. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ /* SECTION Symbols BFD trys to maintain as much symbol information as it can when it moves information from file to file. BFD passes information to applications though the <> 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 infomation passed to applications some targets keep some information 'behind the sceans', 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 was read, but was 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 <>s. This allows applications like the linker to output a symbol as read, since the 'behind the sceens' information will be still available. @menu @* Reading Symbols:: @* Writing Symbols:: @* typedef asymbol:: @* symbol handling functions:: @end menu @node Reading Symbols, Writing Symbols, Symbols, Symbols SUBSECTION Reading Symbols 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 appliction which reads the symbol table: | unsigned int storage_needed; | asymbol **symbol_table; | unsigned int number_of_symbols; | unsigned int i; | | storage_needed = get_symtab_upper_bound (abfd); | | if (storage_needed == 0) { | return ; | } | symbol_table = (asymbol **) bfd_xmalloc (storage_needed); | ... | number_of_symbols = | bfd_canonicalize_symtab (abfd, symbol_table); | | for (i = 0; i < number_of_symbols; i++) { | process_symbol (symbol_table[i]); | } All storage for the symbols themselves is in an obstack connected to the BFD, and is freed when the BFD is closed. @node Writing Symbols, typedef asymbol, Reading Symbols, Symbols SUBSECTION Writing Symbols 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 outputing code must always be provided with an 'owned' symbol; one which has come from another BFD, or one which has been created using <>. 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 <> 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. */ /* @node typedef asymbol, symbol handling functions, Writing Symbols, Symbols */ /* SUBSECTION typedef asymbol An <> has the form: */ /* CODE_FRAGMENT .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 . (invisible to the application writer) information is carried . with the symbol. *} . . struct _bfd *the_bfd; . . {* 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.*} . symvalue value; . . {* Attributes of a symbol: *} . .#define BSF_NO_FLAGS 0x00 . . {* The symbol has local scope; <> in <>. The value . is the offset into the section of the data. *} .#define BSF_LOCAL 0x01 . . {* The symbol has global scope; initialized data in <>. The . value is the offset into the section of the data. *} .#define BSF_GLOBAL 0x02 . . {* Obsolete *} .#define BSF_IMPORT 0x04 . . {* The symbol has global scope, and is exported. The value is . the offset into the section of the data. *} .#define BSF_EXPORT 0x08 . . {* The symbol is undefined. <> in <>. The value has . no meaning. *} .#define BSF_UNDEFINED_OBS 0x10 . . {* The symbol is common, initialized to zero; default in . <>. The value is the size of the object in bytes. *} .#define BSF_FORT_COMM_OBS 0x20 . . {* A normal C symbol would be one of: . <>, <>, <> or . <> *} . . {* The symbol is a debugging record. The value has an arbitary . meaning. *} .#define BSF_DEBUGGING 0x40 . . {* Used by the linker *} .#define BSF_KEEP 0x10000 .#define BSF_KEEP_G 0x80000 . . {* Unused *} .#define BSF_WEAK 0x100000 .#define BSF_CTOR 0x200000 . . {* This symbol was created to point to a section *} .#define BSF_SECTION_SYM 0x400000 . . {* The symbol used to be a common symbol, but now it is . allocated. *} .#define BSF_OLD_COMMON 0x800000 . . {* 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 <> symbol . which is also <> 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 0x40000 . . {* Signal that the symbol is the label of constructor section. *} .#define BSF_CONSTRUCTOR 0x1000000 . . {* Signal that the symbol is a warning symbol. If the symbol . is a warning symbol, then the value field (I know this is . tacky) will point to the asymbol which when referenced will . cause the warning. *} .#define BSF_WARNING 0x2000000 . . {* Signal that the symbol is indirect. The value of the symbol . is a pointer to an undefined asymbol which contains the . name to use instead. *} .#define BSF_INDIRECT 0x4000000 . . 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. This is being phased out in favour . of making this a union. *} . PTR udata; . .} asymbol; */ #include "bfd.h" #include "sysdep.h" #include "libbfd.h" #include "aout/stab_gnu.h" /* @node symbol handling functions, , typedef asymbol, Symbols SUBSECTION Symbol Handling Functions */ /* FUNCTION get_symtab_upper_bound DESCRIPTION Returns the number of bytes required in a vector of pointers to <> for all the symbols in the supplied BFD, including a terminal NULL pointer. If there are no symbols in the BFD, then 0 is returned. .#define get_symtab_upper_bound(abfd) \ . BFD_SEND (abfd, _get_symtab_upper_bound, (abfd)) */ /* FUNCTION bfd_canonicalize_symtab DESCRIPTION Supplied a BFD and a pointer to an uninitialized vector of pointers. This reads in the symbols from the BFD, and fills in the table with pointers to the symbols, and a trailing NULL. The routine returns the actual number of symbol pointers not including the NULL. .#define bfd_canonicalize_symtab(abfd, location) \ . BFD_SEND (abfd, _bfd_canonicalize_symtab,\ . (abfd, location)) */ /* FUNCTION bfd_set_symtab DESCRIPTION Provided a table of pointers to symbols and a count, writes to the output BFD the symbols when closed. SYNOPSIS boolean bfd_set_symtab (bfd *, asymbol **, unsigned int ); */ boolean bfd_set_symtab (abfd, location, symcount) bfd *abfd; asymbol **location; unsigned int symcount; { if ((abfd->format != bfd_object) || (bfd_read_p (abfd))) { bfd_error = invalid_operation; return false; } bfd_get_outsymbols (abfd) = location; bfd_get_symcount (abfd) = symcount; return true; } /* FUNCTION bfd_print_symbol_vandf DESCRIPTION Prints the value and flags of the symbol supplied to the stream file. SYNOPSIS void bfd_print_symbol_vandf(PTR file, asymbol *symbol); */ void DEFUN(bfd_print_symbol_vandf,(file, symbol), PTR file AND asymbol *symbol) { flagword type = symbol->flags; if (symbol->section != (asection *)NULL) { fprintf_vma(file, symbol->value+symbol->section->vma); } else { fprintf_vma(file, symbol->value); } fprintf(file," %c%c%c%c%c%c%c%c", (type & BSF_LOCAL) ? 'l':' ', (type & BSF_GLOBAL) ? 'g' : ' ', (type & BSF_IMPORT) ? 'i' : ' ', (type & BSF_EXPORT) ? 'e' : ' ', (type & BSF_CONSTRUCTOR) ? 'C' : ' ', (type & BSF_WARNING) ? 'W' : ' ', (type & BSF_INDIRECT) ? 'I' : ' ', (type & BSF_DEBUGGING) ? 'd' :' '); } /* FUNCTION bfd_make_empty_symbol DESCRIPTION This function creates a new <> structure for the BFD, and returns a pointer to it. This routine is necessary, since each back end has private information surrounding the <>. Building your own <> 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)) */ /* FUNCTION bfd_decode_symclass DESCRIPTION Return a lower-case character corresponding to the symbol class of symbol. SYNOPSIS int bfd_decode_symclass(asymbol *symbol); */ int DEFUN(bfd_decode_symclass,(symbol), asymbol *symbol) { flagword flags = symbol->flags; if (symbol->section == &bfd_com_section) return 'C'; if (symbol->section == &bfd_und_section) return 'U'; if ( flags & (BSF_GLOBAL|BSF_LOCAL) ) { if ( symbol->section == &bfd_abs_section) return (flags & BSF_GLOBAL) ? 'A' : 'a'; else if ( !strcmp(symbol->section->name, ".text") ) return (flags & BSF_GLOBAL) ? 'T' : 't'; else if ( !strcmp(symbol->section->name, ".data") ) return (flags & BSF_GLOBAL) ? 'D' : 'd'; else if ( !strcmp(symbol->section->name, ".bss") ) return (flags & BSF_GLOBAL) ? 'B' : 'b'; else return (flags & BSF_GLOBAL) ? 'O' : 'o'; } /* We don't have to handle these cases just yet, but we will soon: N_SETV: 'v'; N_SETA: 'l'; N_SETT: 'x'; N_SETD: 'z'; N_SETB: 's'; N_INDR: 'i'; */ return '?'; } bfd_symbol_is_absolute() { abort(); }