syms.c

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/* Generic symbol-table support for the BFD library.
   Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
   2000
   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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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::
@* Mini 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:

|	  long storage_needed;
|	  asymbol **symbol_table;
|	  long number_of_symbols;
|	  long i;
|
|	  storage_needed = bfd_get_symtab_upper_bound (abfd);
|
|         if (storage_needed < 0)
|           FAIL
|
|	  if (storage_needed == 0) {
|	     return ;
|	  }
|	  symbol_table = (asymbol **) xmalloc (storage_needed);
|	    ...
|	  number_of_symbols =
|	     bfd_canonicalize_symtab (abfd, symbol_table);
|
|         if (number_of_symbols < 0)
|           FAIL
|
|	  for (i = 0; i < number_of_symbols; i++) {
|	     process_symbol (symbol_table[i]);
|	  }

	All storage for the symbols themselves is in an objalloc
	connected to the BFD; it is freed when the BFD is closed.

INODE
Writing Symbols, Mini Symbols, 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.

INODE
Mini Symbols, typedef asymbol, Writing Symbols, Symbols
SUBSECTION
	Mini Symbols

	Mini symbols provide read-only access to the symbol table.
	They use less memory space, but require more time to access.
	They can be useful for tools like nm or objdump, which may
	have to handle symbol tables of extremely large executables.

	The <<bfd_read_minisymbols>> function will read the symbols
	into memory in an internal form.  It will return a <<void *>>
	pointer to a block of memory, a symbol count, and the size of
	each symbol.  The pointer is allocated using <<malloc>>, and
	should be freed by the caller when it is no longer needed.

	The function <<bfd_minisymbol_to_symbol>> will take a pointer
	to a minisymbol, and a pointer to a structure returned by
	<<bfd_make_empty_symbol>>, and return a <<asymbol>> structure.
	The return value may or may not be the same as the value from
	<<bfd_make_empty_symbol>> which was passed in.

*/

/*
DOCDD
INODE
typedef asymbol, symbol handling functions, Mini 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, unless BSF_DEBUGGING_RELOC is also set.  *}
.#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.  The name is a
.	   warning.  The name of the next symbol is the one to warn about;
.	   if a reference is made to a symbol with the same name as the next
.	   symbol, a warning is issued by the linker. *}
.#define BSF_WARNING       0x1000
.
.	{* Signal that the symbol is indirect.  This symbol is an indirect
.	   pointer to the symbol with the same name as the next symbol. *}
.#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
.
.       {* The symbol denotes a data object.  Used in ELF, and perhaps
.          others someday.  *}
.#define BSF_OBJECT	   0x10000
.
.       {* This symbol is a debugging symbol.  The value is the offset
.          into the section of the data.  BSF_DEBUGGING should be set
.          as well.  *}
.#define BSF_DEBUGGING_RELOC 0x20000
.
.  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.  *}
.  union
.    {
.      PTR p;
.      bfd_vma i;
.    } udata;
.
.} asymbol;
*/

#include "bfd.h"
#include "sysdep.h"
#include "libbfd.h"
#include "bfdlink.h"
#include "aout/stab_gnu.h"

static char coff_section_type PARAMS ((const char *));

/*
DOCDD
INODE
symbol handling functions,  , typedef asymbol, Symbols
SUBSECTION
	Symbol handling functions
*/

/*
FUNCTION
	bfd_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.  If an error occurs, return -1.

.#define bfd_get_symtab_upper_bound(abfd) \
.     BFD_SEND (abfd, _bfd_get_symtab_upper_bound, (abfd))

*/

/*
FUNCTION
	bfd_is_local_label

SYNOPSIS
        boolean bfd_is_local_label(bfd *abfd, asymbol *sym);

DESCRIPTION
	Return true if the given symbol @var{sym} in the BFD @var{abfd} is
	a compiler generated local label, else return false.
*/

boolean
bfd_is_local_label (abfd, sym)
     bfd *abfd;
     asymbol *sym;
{
  if ((sym->flags & (BSF_GLOBAL | BSF_WEAK)) != 0)
    return false;
  if (sym->name == NULL)
    return false;
  return bfd_is_local_label_name (abfd, sym->name);
}

/*
FUNCTION
	bfd_is_local_label_name

SYNOPSIS
        boolean bfd_is_local_label_name(bfd *abfd, const char *name);

DESCRIPTION
	Return true if a symbol with the name @var{name} in the BFD
	@var{abfd} is a compiler generated local label, else return
	false.  This just checks whether the name has the form of a
	local label.

.#define bfd_is_local_label_name(abfd, name) \
.     BFD_SEND (abfd, _bfd_is_local_label_name, (abfd, name))
*/

/*
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