1991-11-02 22:37:07 +00:00
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/* 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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/*doc*
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@section Constructors
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Classes in C++ have 'constructors' and 'destructors'. These are
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functions which are called automatically by the language whenever data
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of a class is created or destroyed. Class data which is static data
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may also be have a type which requires 'construction', the contructor
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must be called before the data can be referenced, so the contructor
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must be called before the program begins.
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The common solution to this problem is for the compiler to call a
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magic function as the first statement @code{main}. This magic
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function, (often called @code{__main}) runs around calling the
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constructors for all the things needing it.
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With COFF the compile has a bargain with the linker et al. All
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constructors are given strange names, for example
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@code{__GLOBAL__$I$foo} might be the label of a contructor for the
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class @var{foo}. The solution on unfortunate systems (most system V
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machines) is to perform a partial link on all the .o files, do an
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@code{nm} on the result, run @code{awk} or some such over the result
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looking for strange @code{__GLOBAL__$} symbols, generate a C program
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from this, compile it and link with the partially linked input. This
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process is usually called @code{collect}.
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Some versions of @code{a.out} use something called the
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@code{set_vector} mechanism. The constructor symbols are output from
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the compiler with a special stab code saying that they are
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constructors, and the linker can deal with them directly.
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BFD allows applications (ie the linker) to deal with constructor
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information independently of their external implimentation by
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providing a set of entry points for the indiviual object back ends to
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call which maintains a database of the contructor information. The
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application can interrogate the database to find out what it wants.
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The construction data essential for the linker to be able to perform
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its job are:
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@itemize @bullet
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@item asymbol
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The asymbol of the contructor entry point contains all the information
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necessary to call the function.
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@item table id
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The type of symbol, ie is it a contructor, a destructor or something
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else someone dreamed up to make our lives difficult.
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@end itemize
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This module takes this information and then builds extra sections
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attached to the bfds which own the entry points. It creates these
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sections as if they were tables of pointers to the entry points, and
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builds relocation entries to go with them so that the tables can be
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relocated along with the data they reference.
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These sections are marked with a special bit (@code{SEC_CONSTRUCTOR})
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which the linker notices and do with 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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/*proto-internal* bfd_constructor_entry
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This function is called with an a symbol describing the
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function to be called, an string which descibes the xtor type, eg
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something like "CTOR" or "DTOR" would be fine. And the bfd which owns
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the function.
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It's duty is to create a section called "CTOR" or "DTOR" or whatever
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if the bfd doesn't already have one, and grow a relocation table for
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the entry points as they accumulate.
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*; PROTO(void, bfd_constructor_entry,
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(bfd *abfd,
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asymbol **symbol_ptr_ptr,
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1991-11-04 00:35:19 +00:00
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CONST char*type));
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1991-11-02 22:37:07 +00:00
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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->size;
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/* ask the cpu which howto to use */
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reloc->relent.howto =
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bfd_reloc_type_lookup(abfd->arch_info,
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BFD_RELOC_CTOR);
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rel_section->size += sizeof(int *);
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rel_section->reloc_count++;
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}
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}
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