Re: Advice on the prefered way to brand ELF binaries as needed on FreeBSD

[Ulrich Drepper <drepper at redhat dot com>]

"David O'Brien" <obrien@FreeBSD.org> writes:

> Since I don't have a Linux box, could you point me to the proper place in
> the Binutils code?

There is no binutils change needed.  Create a .note section and put an
appropriate record for the OS in it.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/* Special .init and .fini section support.
   Copyright (C) 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it
   and/or modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   In addition to the permissions in the GNU Library General Public
   License, the Free Software Foundation gives you unlimited
   permission to link the compiled version of this file with other
   programs, and to distribute those programs without any restriction
   coming from the use of this file.  (The Library General Public
   License restrictions do apply in other respects; for example, they
   cover modification of the file, and distribution when not linked
   into another program.)

   The GNU C Library 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 Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* Define an ELF note identifying the operating-system ABI that the
   executable was created for.  The ELF note information identifies a
   particular OS or coordinated development effort within which the
   ELF header's e_machine value plus (for dynamically linked programs)
   the PT_INTERP dynamic linker name and DT_NEEDED shared library
   names fully identify the runtime environment required by an
   executable.

   The general format of ELF notes is as follows.
   Offsets and lengths are bytes or (parenthetical references) to the
   values in other fields.

offset	length	contents	
0	4	length of name
4	4	length of data
8	4	note type
12	(0)	vendor name
		- null-terminated ASCII string, padded to 4-byte alignment
12+(0)	(4)	note data, 

   The GNU project and cooperating development efforts (including the
   Linux community) use note type 1 and a vendor name string of "GNU"
   for a note descriptor that indicates ABI requirements.  The note data
   is four 32-bit words.  The first of these is an operating system
   number (0=Hurd, 1=Linux, 2=Solaris, ...) and the remaining three
   identify the earliest release of that OS that supports this ABI.
   See abi-tags (top level) for details. */

#include <abi-tag.h>		/* OS-specific ABI tag value */
	
/* The linker (GNU ld 2.8 and later) recognizes an allocated section whose
   name begins with `.note' and creates a PT_NOTE program header entry
   pointing at it. */

	.section ".note.ABI-tag", "a"
	.align 4
	.long 1f - 0f		/* name length */
	.long 3f - 2f		/* data length */
	.long  1		/* note type */
0:	.asciz "GNU"		/* vendor name */
1:	.align 4		
2:	.long ABI_TAG		/* note data: the ABI tag */
3:	.align 4		/* pad out section */
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Define ABI_TAG to something like

#define ABI_TAG 0,2,0,0

(This is the Linux version.  It comes from a file in glibc which contains

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.*-.*-linux.*           0       2.0.0   # earliest compatible kernel version

.*-.*-gnu-gnu.*         1       0.0.0

.*-sun-solaris2.*       2       2.0.0   # just an arbitrary value
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Pick your own values.


-- 
---------------.      drepper at gnu.org  ,-.   1325 Chesapeake Terrace
Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
Red Hat          `--' drepper at redhat.com   `------------------------