452 lines
12 KiB
C
452 lines
12 KiB
C
/* Generic symbol-table support for the BFD library.
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Copyright (C) 1990-1991 Free Software Foundation, Inc.
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Written by Cygnus Support.
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This file is part of BFD, the Binary File Descriptor library.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
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/*
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SECTION
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Symbols
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DESCRIPTION
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BFD trys to maintain as much symbol information as it can when
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it moves information from file to file. BFD passes information
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to applications though the <<asymbol>> structure. When the
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applicationrequests the symbol table, BFD reads the table in
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the native form and translates parts of it into the internal
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format. To maintain more than the infomation passed to
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applications some targets keep some information 'behind the
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sceans', in a structure only the particular back end knows
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about. For example, the coff back end keeps the original
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symbol table structure as well as the canonical structure when
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a BFD is read in. On output, the coff back end can reconstruct
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the output symbol table so that no information is lost, even
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information unique to coff which BFD doesn't know or
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understand. If a coff symbol table was read, but was written
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through an a.out back end, all the coff specific information
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would be lost. (.. until BFD 2 :). The symbol table of a BFD
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is not necessarily read in until a canonicalize request is
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made. Then the BFD back end fills in a table provided by the
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application with pointers to the canonical information. To
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output symbols, the application provides BFD with a table of
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pointers to pointers to <<asymbol>>s. This allows applications
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like the linker to output a symbol as read, since the 'behind
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the sceens' information will be still available.
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@menu
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* Reading Symbols::
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* Writing Symbols::
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* typedef asymbol::
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* symbol handling functions::
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@end menu
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@node Reading Symbols, Writing Symbols, Symbols, Symbols
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SUBSECTION
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Reading Symbols
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DESCRIPTION
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There are two stages to reading a symbol table from a BFD;
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allocating storage, and the actual reading process. This is an
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excerpt from an appliction which reads the symbol table:
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EXAMPLE
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unsigned int storage_needed;
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asymbol **symbol_table;
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unsigned int number_of_symbols;
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unsigned int i;
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storage_needed = get_symtab_upper_bound (abfd);
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if (storage_needed == 0) {
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return ;
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}
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symbol_table = (asymbol **) bfd_xmalloc (storage_needed);
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...
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number_of_symbols =
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bfd_canonicalize_symtab (abfd, symbol_table);
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for (i = 0; i < number_of_symbols; i++) {
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process_symbol (symbol_table[i]);
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}
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DESCRIPTION
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All storage for the symbols themselves is in an obstack
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connected to the BFD, and is freed when the BFD is closed.
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@node Writing Symbols, typedef asymbol, Reading Symbols, Symbols
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SUBSECTION
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Writing Symbols
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DESCRIPTION
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Writing of a symbol table is automatic when a BFD open for
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writing is closed. The application attaches a vector of
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pointers to pointers to symbols to the BFD being written, and
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fills in the symbol count. The close and cleanup code reads
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through the table provided and performs all the necessary
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operations. The outputing code must always be provided with an
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'owned' symbol; one which has come from another BFD, or one
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which has been created using <<bfd_make_empty_symbol>>. An
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example showing the creation of a symbol table with only one element:
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EXAMPLE
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#include "bfd.h"
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main()
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{
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bfd *abfd;
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asymbol *ptrs[2];
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asymbol *new;
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abfd = bfd_openw("foo","a.out-sunos-big");
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bfd_set_format(abfd, bfd_object);
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new = bfd_make_empty_symbol(abfd);
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new->name = "dummy_symbol";
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new->section = (asection *)0;
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new->flags = BSF_ABSOLUTE | BSF_GLOBAL;
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new->value = 0x12345;
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ptrs[0] = new;
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ptrs[1] = (asymbol *)0;
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bfd_set_symtab(abfd, ptrs, 1);
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bfd_close(abfd);
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}
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./makesym
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nm foo
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00012345 A dummy_symbol
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DESCRIPTION
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Many formats cannot represent arbitary symbol information; for
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instance the <<a.out>> object format does not allow an
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arbitary number of sections. A symbol pointing to a section
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which is not one of <<.text>>, <<.data>> or <<.bss>> cannot
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be described.
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*/
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/*doc*
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@node typedef asymbol, symbol handling functions, Writing Symbols, Symbols
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*/
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/*
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TYPEDEF
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typedef asymbol
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DESCRIPTION
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An <<asymbol>> has the form:
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.typedef struct symbol_cache_entry
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.{
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A pointer to the BFD which owns the symbol. This information
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is necessary so that a back end can work out what additional
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(invisible to the application writer) information is carried
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with the symbol.
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. struct _bfd *the_bfd;
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The text of the symbol. The name is left alone, and not copied - the
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application may not alter it.
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. CONST char *name;
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The value of the symbol.
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. symvalue value;
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Attributes of a symbol:
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.#define BSF_NO_FLAGS 0x00
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The symbol has local scope; <<static>> in <<C>>. The value is
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the offset into the section of the data.
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.#define BSF_LOCAL 0x01
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The symbol has global scope; initialized data in <<C>>. The value
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is the offset into the section of the data.
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.#define BSF_GLOBAL 0x02
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Obsolete
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.#define BSF_IMPORT 0x04
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The symbol has global scope, and is exported. The value is the offset
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into the section of the data.
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.#define BSF_EXPORT 0x08
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The symbol is undefined. <<extern>> in <<C>>. The value has no meaning.
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.#define BSF_UNDEFINED 0x10
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The symbol is common, initialized to zero; default in <<C>>. The
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value is the size of the object in bytes.
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.#define BSF_FORT_COMM 0x20
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A normal <<C>> symbol would be one of:
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<<BSF_LOCAL>>, <<BSF_FORT_COMM>>, <<BSF_UNDEFINED>> or <<BSF_EXPORT|BSD_GLOBAL>>
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The symbol is a debugging record. The value has an arbitary meaning.
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.#define BSF_DEBUGGING 0x40
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The symbol has no section attached, any value is the actual value and
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is not a relative offset to a section.
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.#define BSF_ABSOLUTE 0x80
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Used by the linker
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.#define BSF_KEEP 0x10000
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.#define BSF_KEEP_G 0x80000
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Unused
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.#define BSF_WEAK 0x100000
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.#define BSF_CTOR 0x200000
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.#define BSF_FAKE 0x400000
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The symbol used to be a common symbol, but now it is allocated.
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.#define BSF_OLD_COMMON 0x800000
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The default value for common data.
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.#define BFD_FORT_COMM_DEFAULT_VALUE 0
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In some files the type of a symbol sometimes alters its location
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in an output file - ie in coff a <<ISFCN>> symbol which is also <<C_EXT>>
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symbol appears where it was declared and not at the end of a section.
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This bit is set by the target BFD part to convey this information.
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.#define BSF_NOT_AT_END 0x40000
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Signal that the symbol is the label of constructor section.
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.#define BSF_CONSTRUCTOR 0x1000000
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Signal that the symbol is a warning symbol. If the symbol is a warning
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symbol, then the value field (I know this is tacky) will point to the
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asymbol which when referenced will cause the warning.
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.#define BSF_WARNING 0x2000000
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Signal that the symbol is indirect. The value of the symbol is a
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pointer to an undefined asymbol which contains the name to use
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instead.
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.#define BSF_INDIRECT 0x4000000
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. flagword flags;
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A pointer to the section to which this symbol is relative, or 0 if the
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symbol is absolute or undefined. Note that it is not sufficient to set
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this location to 0 to mark a symbol as absolute - the flag
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<<BSF_ABSOLUTE>> must be set also.
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. struct sec *section;
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Back end special data. This is being phased out in favour of making
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this a union.
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. PTR udata;
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.} asymbol;
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*/
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#include "bfd.h"
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#include "sysdep.h"
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#include "libbfd.h"
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#include "stab.gnu.h"
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/*
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@node symbol handling functions, , typedef asymbol, Symbols
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SUBSECTION
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Symbol Handling Functions
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*/
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/*
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FUNCTION
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get_symtab_upper_bound
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DESCRIPTION
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Returns the number of bytes required in a vector of pointers
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to <<asymbols>> for all the symbols in the supplied BFD,
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including a terminal NULL pointer. If there are no symbols in
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the BFD, then 0 is returned.
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.#define get_symtab_upper_bound(abfd) \
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. BFD_SEND (abfd, _get_symtab_upper_bound, (abfd))
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*/
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/*
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FUNCTION
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bfd_canonicalize_symtab
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DESCRIPTION
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Supplied a BFD and a pointer to an uninitialized vector of
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pointers. This reads in the symbols from the BFD, and fills in
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the table with pointers to the symbols, and a trailing NULL.
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The routine returns the actual number of symbol pointers not
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including the NULL.
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.#define bfd_canonicalize_symtab(abfd, location) \
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. BFD_SEND (abfd, _bfd_canonicalize_symtab,\
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. (abfd, location))
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*/
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/*
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FUNCTION
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bfd_set_symtab
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DESCRIPTION
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Provided a table of pointers to symbols and a count, writes to
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the output BFD the symbols when closed.
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SYNOPSIS
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boolean bfd_set_symtab (bfd *, asymbol **, unsigned int );
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*/
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boolean
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bfd_set_symtab (abfd, location, symcount)
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bfd *abfd;
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asymbol **location;
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unsigned int symcount;
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{
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if ((abfd->format != bfd_object) || (bfd_read_p (abfd))) {
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bfd_error = invalid_operation;
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return false;
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}
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bfd_get_outsymbols (abfd) = location;
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bfd_get_symcount (abfd) = symcount;
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return true;
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}
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/*
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FUNCTION
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bfd_print_symbol_vandf
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DESCRIPTION
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Prints the value and flags of the symbol supplied to the stream file.
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SYNOPSIS
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void bfd_print_symbol_vandf(PTR file, asymbol *symbol);
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*/
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void
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DEFUN(bfd_print_symbol_vandf,(file, symbol),
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PTR file AND
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asymbol *symbol)
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{
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flagword type = symbol->flags;
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if (symbol->section != (asection *)NULL)
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{
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fprintf_vma(file, symbol->value+symbol->section->vma);
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}
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else
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{
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fprintf_vma(file, symbol->value);
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}
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fprintf(file," %c%c%c%c%c%c%c%c%c%c",
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(type & BSF_LOCAL) ? 'l':' ',
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(type & BSF_GLOBAL) ? 'g' : ' ',
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(type & BSF_IMPORT) ? 'i' : ' ',
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(type & BSF_EXPORT) ? 'e' : ' ',
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(type & BSF_UNDEFINED) ? 'u' : ' ',
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(type & BSF_FORT_COMM) ? 'c' : ' ',
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(type & BSF_CONSTRUCTOR) ? 'C' : ' ',
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(type & BSF_WARNING) ? 'W' : ' ',
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(type & BSF_INDIRECT) ? 'I' : ' ',
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(type & BSF_DEBUGGING) ? 'd' :' ');
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}
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/*
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FUNCTION
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bfd_make_empty_symbol
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DESCRIPTION
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This function creates a new <<asymbol>> structure for the BFD,
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and returns a pointer to it.
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This routine is necessary, since each back end has private
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information surrounding the <<asymbol>>. Building your own
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<<asymbol>> and pointing to it will not create the private
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information, and will cause problems later on.
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.#define bfd_make_empty_symbol(abfd) \
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. BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
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*/
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/*
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FUNCTION
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bfd_decode_symclass
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DESCRIPTION
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Return a lower-case character corresponding to the symbol
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class of symbol.
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SYNOPSIS
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int bfd_decode_symclass(asymbol *symbol);
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*/
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int
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DEFUN(bfd_decode_symclass,(symbol),
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asymbol *symbol)
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{
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flagword flags = symbol->flags;
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if (flags & BSF_FORT_COMM) return 'C';
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if (flags & BSF_UNDEFINED) return 'U';
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if (flags & BSF_ABSOLUTE)
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return (flags & BSF_GLOBAL) ? 'A' : 'a';
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if ( flags & (BSF_GLOBAL|BSF_LOCAL) ) {
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if (symbol->section == (asection *)NULL)
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return '*';
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else if ( !strcmp(symbol->section->name, ".text") )
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return (flags & BSF_GLOBAL) ? 'T' : 't';
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else if ( !strcmp(symbol->section->name, ".data") )
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return (flags & BSF_GLOBAL) ? 'D' : 'd';
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else if ( !strcmp(symbol->section->name, ".bss") )
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return (flags & BSF_GLOBAL) ? 'B' : 'b';
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else
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return (flags & BSF_GLOBAL) ? 'O' : 'o';
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}
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/* We don't have to handle these cases just yet, but we will soon:
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N_SETV: 'v';
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N_SETA: 'l';
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N_SETT: 'x';
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N_SETD: 'z';
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N_SETB: 's';
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N_INDR: 'i';
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*/
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return '?';
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}
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