/* Generic symbol-table support for the BFD library. Copyright (C) 1990, 1991, 1992, 1993 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 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 <<asymbol>>s. This allows applications like the linker to output a symbol as it was read, since the ``behind the scenes'' information will be still available. @menu @* Reading Symbols:: @* Writing Symbols:: @* typedef asymbol:: @* symbol handling functions:: @end menu INODE 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 application 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 **) 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; it is freed when the BFD is closed. INODE 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 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. */ /* DOCDD INODE typedef asymbol, symbol handling functions, Writing Symbols, Symbols */ /* SUBSECTION typedef asymbol An <<asymbol>> 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 . 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. 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 0x1000 . . {* 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 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 . . 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" /* DOCDD INODE symbol handling functions, , typedef asymbol, Symbols SUBSECTION Symbol handling functions */ /* FUNCTION 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 @var{abfd}, including a terminal NULL pointer. If there are no symbols in the BFD, then return 0. .#define get_symtab_upper_bound(abfd) \ . BFD_SEND (abfd, _get_symtab_upper_bound, (abfd)) */ /* FUNCTION bfd_canonicalize_symtab DESCRIPTION Read the symbols from the BFD @var{abfd}, and fills in the vector @var{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)) */ /* FUNCTION bfd_set_symtab SYNOPSIS boolean bfd_set_symtab (bfd *abfd, asymbol **location, unsigned int count); DESCRIPTION Arrange that when the output BFD @var{abfd} is closed, the table @var{location} of @var{count} pointers to symbols will be written. */ boolean bfd_set_symtab (abfd, location, symcount) bfd *abfd; asymbol **location; unsigned int symcount; { if ((abfd->format != bfd_object) || (bfd_read_p (abfd))) { bfd_set_error (bfd_error_invalid_operation); return false; } bfd_get_outsymbols (abfd) = location; bfd_get_symcount (abfd) = symcount; return true; } /* FUNCTION bfd_print_symbol_vandf SYNOPSIS void bfd_print_symbol_vandf(PTR file, asymbol *symbol); DESCRIPTION Print the value and flags of the @var{symbol} supplied to the stream @var{file}. */ void bfd_print_symbol_vandf (arg, symbol) PTR arg; asymbol *symbol; { FILE *file = (FILE *) arg; flagword type = symbol->flags; if (symbol->section != (asection *) NULL) { fprintf_vma (file, symbol->value + symbol->section->vma); } else { fprintf_vma (file, symbol->value); } /* This presumes that a symbol can not be both BSF_DEBUGGING and BSF_DYNAMIC. */ fprintf (file, " %c%c%c%c%c%c%c", (type & BSF_LOCAL) ? 'l' : ' ', (type & BSF_GLOBAL) ? 'g' : ' ', (type & BSF_WEAK) ? 'w' : ' ', (type & BSF_CONSTRUCTOR) ? 'C' : ' ', (type & BSF_WARNING) ? 'W' : ' ', (type & BSF_INDIRECT) ? 'I' : ' ', (type & BSF_DEBUGGING) ? 'd' : (type & BSF_DYNAMIC) ? 'D' : ' '); } /* FUNCTION bfd_make_empty_symbol DESCRIPTION Create a new <<asymbol>> structure for the BFD @var{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)) */ /* FUNCTION bfd_make_debug_symbol DESCRIPTION Create a new <<asymbol>> structure for the BFD @var{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)) */ struct section_to_type { CONST char *section; char type; }; /* Map section names to POSIX/BSD single-character symbol types. This table is probably incomplete. It is sorted for convenience of adding entries. Since it is so short, a linear search is used. */ static CONST struct section_to_type stt[] = { {"*DEBUG*", 'N'}, {".bss", 'b'}, {".data", 'd'}, {".sbss", 's'}, /* Small BSS (uninitialized data) */ {".scommon", 'c'}, /* Small common */ {".sdata", 'g'}, /* Small initialized data */ {".text", 't'}, {0, 0} }; /* Return the single-character symbol type corresponding to section S, or '?' for an unknown COFF section. */ static char coff_section_type (s) char *s; { CONST struct section_to_type *t; for (t = &stt[0]; t->section; t++) if (!strcmp (s, t->section)) return t->type; return '?'; } #ifndef islower #define islower(c) ((c) >= 'a' && (c) <= 'z') #endif #ifndef toupper #define toupper(c) (islower(c) ? ((c) & ~0x20) : (c)) #endif /* FUNCTION bfd_decode_symclass DESCRIPTION Return a character corresponding to the symbol class of @var{symbol}, or '?' for an unknown class. SYNOPSIS int bfd_decode_symclass(asymbol *symbol); */ int bfd_decode_symclass (symbol) asymbol *symbol; { char c; if (bfd_is_com_section (symbol->section)) return 'C'; if (symbol->section == &bfd_und_section) return 'U'; if (symbol->section == &bfd_ind_section) return 'I'; if (!(symbol->flags & (BSF_GLOBAL | BSF_LOCAL))) return '?'; if (symbol->section == &bfd_abs_section) c = 'a'; else if (symbol->section) c = coff_section_type (symbol->section->name); else return '?'; if (symbol->flags & BSF_GLOBAL) c = toupper (c); return c; /* 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'; */ } /* FUNCTION 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); */ void bfd_symbol_info (symbol, ret) asymbol *symbol; symbol_info *ret; { ret->type = bfd_decode_symclass (symbol); if (ret->type != 'U') ret->value = symbol->value + symbol->section->vma; else ret->value = 0; ret->name = symbol->name; } void bfd_symbol_is_absolute () { abort (); }