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 @dfn{constructors} and @dfn{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 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 before <<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 compiler 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 (i.e., the linker) to deal with
  58         constructor information independently of their external
  59         implementation by providing a set of entry points for the
  60         indiviual object back ends to call to maintain 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, i.e., is it a constructor, a destructor or
  72         something else someone dreamed up to make our lives difficult.
  73
  74         The constructor module takes this information and 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 does 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         @var{symbol_ptr_ptr} describes the
 105         function to be called; @var{type} descibes the xtor type,
 106         e.g., something like "CTOR" or "DTOR" would be fine.  @var{abfd}
 107         is the BFD which owns the function.  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     /* Look up the section we're using to store the table in */
 121     asection *rel_section = bfd_get_section_by_name (abfd, type);
 122     if (rel_section == (asection *)NULL) {
 123         rel_section = bfd_make_section (abfd, type);
 124         rel_section->flags = SEC_CONSTRUCTOR;
 125         rel_section->alignment_power = 2;
 126     }
 127
 128     /* Create a relocation into the section which references the entry
 129        point */
 130    {
 131        arelent_chain *reloc = (arelent_chain *)bfd_alloc(abfd,
 132                                                          sizeof(arelent_chain));
 133
 134 /*       reloc->relent.section = (asection *)NULL;*/
 135        reloc->relent.addend = 0;
 136
 137        reloc->relent.sym_ptr_ptr = symbol_ptr_ptr;
 138        reloc->next = rel_section->constructor_chain;
 139        rel_section->constructor_chain = reloc;
 140        reloc->relent.address = rel_section->_cooked_size;
 141        /* ask the cpu which howto to use */
 142        reloc->relent.howto = bfd_reloc_type_lookup(abfd, BFD_RELOC_CTOR);
 143        rel_section->_cooked_size += sizeof(int *);
 144        rel_section->reloc_count++;
 145    }
 146
 147 }