372 lines
10 KiB
C
372 lines
10 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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/*doc*
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@section Symbols
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BFD trys to maintain as much symbol information as it can when it
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moves information from file to file. BFD passes information to
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applications though the @code{asymbol} structure. When the application
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requests the symbol table, BFD reads the table in the native form and
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translates parts of it into the internal format. To maintain more than
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the infomation passed to applications some targets keep
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some information 'behind the sceans', in a structure only the
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particular back end knows about. For example, the coff back end keeps
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the original symbol table structure as well as the canonical structure
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when 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 understand. If a
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coff symbol table was read, but was written through an a.out back end,
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all the coff specific information would be lost. (.. until BFD 2 :).
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The symbol table of a BFD is not necessarily read in until a
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canonicalize request is made. Then the BFD back end fills in a table
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provided by the application with pointers to the canonical
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information.
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To output symbols, the application provides BFD with a table of
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pointers to pointers to @code{asymbol}s. This allows applications like
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the linker to output a symbol as read, since the 'behind the sceens'
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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 Reading Symbols
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There are two stages to reading a symbol table from a BFD; allocating
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storage, and the actual reading process. This is an excerpt from an
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appliction which reads the symbol table:
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*+
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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 **) malloc (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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*-
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All storage for the symbols themselves is in an obstack connected to
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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 Writing Symbols
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Writing of a symbol table is automatic when a BFD open for writing
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is closed. The application attaches a vector of pointers to pointers to symbols
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to the BFD being written, and fills in the symbol count. The close and
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cleanup code reads through the table provided and performs all the
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necessary operations. The outputing code must always be provided with
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an 'owned' symbol; one which has come from another BFD, or one which
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has been created using @code{bfd_make_empty_symbol}.
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An example showing the creation of a symbol table with only one
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element:
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*+
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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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*-
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Many formats cannot represent arbitary symbol information; for
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instance the @code{a.out} object format does not allow an arbitary
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number of sections. A symbol pointing to a section which is not one of
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@code{.text}, @code{.data} or @code{.bss} cannot 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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/*proto*
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@subsection typedef asymbol
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An @code{asymbol} has the form:
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*+++
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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 is
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necessary so that a back end can work out what additional (invisible to
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the application writer) information is carried 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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$#define BSF_NO_FLAGS 0x00
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The symbol has local scope; @code{static} in @code{C}. The value is
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the offset into the section of the data.
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$#define BSF_LOCAL 0x01
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The symbol has global scope; initialized data in @code{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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$#define BSF_EXPORT 0x08
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The symbol is undefined. @code{extern} in @code{C}. The value has no meaning.
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$#define BSF_UNDEFINED 0x10
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The symbol is common, initialized to zero; default in @code{C}. The
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value is the size of the object in bytes.
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$#define BSF_FORT_COMM 0x20
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A normal @code{C} symbol would be one of:
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@code{BSF_LOCAL}, @code{BSF_FORT_COMM}, @code{BSF_UNDEFINED} or @code{BSF_EXPORT|BSD_GLOBAL}
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The symbol is a debugging record. The value has an arbitary meaning.
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$#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 @code{ISFCN} symbol which is also @code{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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Aointer 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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@code{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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*/
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#include "sysdep.h"
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#include "bfd.h"
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#include "libbfd.h"
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/*doc*
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@node symbol handling functions, Symbols, typedef asymbol, Symbols
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@subsection Symbol Handling Functions
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*/
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/*proto* get_symtab_upper_bound
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Returns the number of bytes required in a vector of pointers to
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@code{asymbols} for all the symbols in the supplied BFD, including a
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terminal NULL pointer. If there are no symbols in the BFD, then 0 is
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returned.
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*+
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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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/*proto* bfd_canonicalize_symtab
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Supplied a BFD and a pointer to an uninitialized vector of pointers.
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This reads in the symbols from the BFD, and fills in the table with
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pointers to the symbols, and a trailing NULL. The routine returns the
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actual number of symbol pointers not including the NULL.
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*+
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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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/*proto* bfd_set_symtab
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Provided a table of pointers to to symbols and a count, writes to the
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output BFD the symbols when closed.
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*; PROTO(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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/*proto* bfd_print_symbol_vandf
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Prints the value and flags of the symbol supplied to the stream file.
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*; PROTO(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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/*proto* bfd_make_empty_symbol
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This function creates a new @code{asymbol} structure for the BFD, and
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returns a pointer to it.
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This routine is necessary, since each back end has private information
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surrounding the @code{asymbol}. Building your own @code{asymbol} and
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pointing to it will not create the private information, and will cause
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problems later on.
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*+
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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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