bfd/ctor.c

   1 /* BFD library support routines for constructors
   2    Copyright (C) 1990-1991 Free Software Foundation, Inc.
   3
   4    Hacked by Steve Chamberlain of Cygnus Support. With some help from
   5    Judy Chamberlain too.
   6
   7
   8 This file is part of BFD, the Binary File Descriptor library.
   9
  10 This program is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU General Public License as published by
  12 the Free Software Foundation; either version 2 of the License, or
  13 (at your option) any later version.
  14
  15 This program is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with this program; if not, write to the Free Software
  22 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  23
  24 /*
  25 SECTION
  26         Constructors
  27
  28         Classes in C++ have 'constructors' and 'destructors'.  These
  29         are functions which are called automatically by the language
  30         whenever data of a class is created or destroyed.  Class data
  31         which is static data may also be have a type which requires
  32         'construction', the contructor must be called before the data
  33         can be referenced, so the contructor must be called before the
  34         program begins.
  35
  36         The common solution to this problem is for the compiler to
  37         call a magic function as the first statement <<main>>.
  38         This magic function, (often called <<__main>>) runs around
  39         calling the constructors for all the things needing it.
  40
  41         With COFF the compile has a bargain with the linker et al.
  42         All constructors are given strange names, for example
  43         <<__GLOBAL__$I$foo>> might be the label of a contructor for
  44         the class @var{foo}.  The solution on unfortunate systems
  45         (most system V machines) is to perform a partial link on all
  46         the .o files, do an <<nm>> on the result, run <<awk>> or some
  47         such over the result looking for strange <<__GLOBAL__$>>
  48         symbols, generate a C program from this, compile it and link
  49         with the partially linked input. This process is usually
  50         called <<collect>>.
  51
  52         Some versions of <<a.out>> use something called the
  53         <<set_vector>> mechanism.  The constructor symbols are output
  54         from the compiler with a special stab code saying that they
  55         are constructors, and the linker can deal with them directly.
  56
  57         BFD allows applications (ie the linker) to deal with
  58         constructor information independently of their external
  59         implimentation by providing a set of entry points for the
  60         indiviual object back ends to call which maintains a database
  61         of the contructor information.  The application can
  62         interrogate the database to find out what it wants.  The
  63         construction data essential for the linker to be able to
  64         perform its job are:
  65
  66         o asymbol
  67         The asymbol of the contructor entry point contains all the
  68         information necessary to call the function.
  69
  70         o table id
  71         The type of symbol, ie is it a contructor, a destructor or
  72         something else someone dreamed up to make our lives difficult.
  73
  74         This module takes this information and then builds extra
  75         sections attached to the bfds which own the entry points.  It
  76         creates these sections as if they were tables of pointers to
  77         the entry points, and builds relocation entries to go with
  78         them so that the tables can be relocated along with the data
  79         they reference.
  80
  81         These sections are marked with a special bit
  82         (<<SEC_CONSTRUCTOR>>) which the linker notices and do with
  83         what it wants.
  84
  85 */
  86
  87 #include <bfd.h>
  88 #include <sysdep.h>
  89 #include <libbfd.h>
  90
  91
  92
  93 /*
  94 INTERNAL_FUNCTION
  95         bfd_constructor_entry
  96
  97 SYNOPSIS
  98         void bfd_constructor_entry(bfd *abfd,
  99                 asymbol **symbol_ptr_ptr,
 100                 CONST char*type);
 101
 102
 103 DESCRIPTION
 104         This function is called with an a symbol describing the
 105         function to be called, an string which descibes the xtor type,
 106         eg something like "CTOR" or "DTOR" would be fine. And the bfd
 107         which owns the function. Its duty is to create a section
 108         called "CTOR" or "DTOR" or whatever if the bfd doesn't already
 109         have one, and grow a relocation table for the entry points as
 110         they accumulate.
 111
 112 */
 113
 114
 115 void DEFUN(bfd_constructor_entry,(abfd, symbol_ptr_ptr, type),
 116            bfd *abfd AND
 117            asymbol **symbol_ptr_ptr AND
 118            CONST char *type)
 119
 120 {
 121     /* Look up the section we're using to store the table in */
 122     asection *rel_section = bfd_get_section_by_name (abfd, type);
 123     if (rel_section == (asection *)NULL) {
 124         rel_section = bfd_make_section (abfd, type);
 125         rel_section->flags = SEC_CONSTRUCTOR;
 126         rel_section->alignment_power = 2;
 127     }
 128
 129     /* Create a relocation into the section which references the entry
 130        point */
 131    {
 132        arelent_chain *reloc = (arelent_chain *)bfd_alloc(abfd,
 133                                                          sizeof(arelent_chain));
 134
 135 /*       reloc->relent.section = (asection *)NULL;*/
 136        reloc->relent.addend = 0;
 137
 138        reloc->relent.sym_ptr_ptr = symbol_ptr_ptr;
 139        reloc->next = rel_section->constructor_chain;
 140        rel_section->constructor_chain = reloc;
 141        reloc->relent.address = rel_section->_cooked_size;
 142        /* ask the cpu which howto to use */
 143        reloc->relent.howto = bfd_reloc_type_lookup(abfd, BFD_RELOC_CTOR);
 144        rel_section->_cooked_size += sizeof(int *);
 145        rel_section->reloc_count++;
 146    }
 147
 148 }