147 lines
5.2 KiB
C
147 lines
5.2 KiB
C
/* BFD library support routines for constructors
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Copyright (C) 1990-1991 Free Software Foundation, Inc.
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Hacked by Steve Chamberlain of Cygnus Support. With some help from
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Judy Chamberlain too.
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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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Constructors
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Classes in C++ have @dfn{constructors} and @dfn{destructors}. These
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are functions which are called automatically by the language
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whenever data of a class is created or destroyed. Class data
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which is static may also be have a type which requires
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`construction'; the contructor must be called before the data
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can be referenced, so the contructor must be called before the
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program begins.
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The common solution to this problem is for the compiler to
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call a magic function as the first statement before <<main>>.
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This magic function (often called <<__main>>) runs around
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calling the constructors for all the things needing it.
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With COFF, the compiler has a bargain with the linker et al.
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All constructors are given strange names; for example,
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<<__GLOBAL__$I$foo>> might be the label of a contructor for
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the class @var{foo}. The solution on unfortunate systems
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(most System V machines) is to perform a partial link on all
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the <<.o>> files, do an <<nm>> on the result, run <<awk>> or some
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such over the result looking for strange <<__GLOBAL__$>>
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symbols, generate a C program from this, compile it, and link
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with the partially linked input. This process is usually
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called <<collect>>.
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Some versions of <<a.out>> use something called the
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<<set_vector>> mechanism. The constructor symbols are output
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from the compiler with a special stab code saying that they
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are constructors, and the linker can deal with them directly.
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BFD allows applications (i.e., the linker) to deal with
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constructor information independently of their external
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implementation by providing a set of entry points for the
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indiviual object back ends to call to maintain a database
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of the contructor information. The application can
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interrogate the database to find out what it wants. The
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construction data essential for the linker to be able to
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perform its job are:
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o asymbol -
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The asymbol of the contructor entry point contains all the
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information necessary to call the function.
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o table id -
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The type of symbol, i.e., is it a constructor, a destructor or
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something else someone dreamed up to make our lives difficult.
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The constructor module takes this information and builds extra
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sections attached to the BFDs which own the entry points. It
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creates these sections as if they were tables of pointers to
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the entry points, and builds relocation entries to go with
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them so that the tables can be relocated along with the data
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they reference.
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These sections are marked with a special bit
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(<<SEC_CONSTRUCTOR>>), which the linker notices and does with
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what it wants.
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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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/*
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INTERNAL_FUNCTION
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bfd_constructor_entry
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SYNOPSIS
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void bfd_constructor_entry(bfd *abfd,
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asymbol **symbol_ptr_ptr,
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CONST char*type);
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DESCRIPTION
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@var{symbol_ptr_ptr} describes the
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function to be called; @var{type} descibes the xtor type,
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e.g., something like "CTOR" or "DTOR" would be fine. @var{abfd}
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is the BFD which owns the function. Create a section
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called "CTOR" or "DTOR" or whatever if the BFD doesn't already
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have one, and grow a relocation table for the entry points as
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they accumulate.
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*/
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void DEFUN(bfd_constructor_entry,(abfd, symbol_ptr_ptr, type),
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bfd *abfd AND
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asymbol **symbol_ptr_ptr AND
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CONST char *type)
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{
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/* Look up the section we're using to store the table in */
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asection *rel_section = bfd_get_section_by_name (abfd, type);
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if (rel_section == (asection *)NULL) {
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rel_section = bfd_make_section (abfd, type);
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rel_section->flags = SEC_CONSTRUCTOR;
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rel_section->alignment_power = 2;
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}
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/* Create a relocation into the section which references the entry
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point */
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{
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arelent_chain *reloc = (arelent_chain *)bfd_alloc(abfd,
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sizeof(arelent_chain));
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/* reloc->relent.section = (asection *)NULL;*/
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reloc->relent.addend = 0;
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reloc->relent.sym_ptr_ptr = symbol_ptr_ptr;
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reloc->next = rel_section->constructor_chain;
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rel_section->constructor_chain = reloc;
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reloc->relent.address = rel_section->_cooked_size;
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/* ask the cpu which howto to use */
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reloc->relent.howto = bfd_reloc_type_lookup(abfd, BFD_RELOC_CTOR);
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rel_section->_cooked_size += sizeof(int *);
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rel_section->reloc_count++;
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}
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}
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