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__executable_start (was: [bug #17644] glibc: support for TLS)

From: Thomas Schwinge <thomas at codesourcery dot com>
To: Roland McGrath <roland at hack dot frob dot com>, <libc-alpha at sourceware dot org>
Cc: Samuel Thibault <samuel dot thibault at ens-lyon dot org>, <bug-hurd at gnu dot org>
Date: Sun, 26 May 2013 16:38:23 +0200
Subject: __executable_start (was: [bug #17644] glibc: support for TLS)
References: <20061106-162243 dot sv33391 dot 95744 at savannah dot gnu dot org> <20061106-163926 dot sv33391 dot 3217 at savannah dot gnu dot org> <20070612-021101 dot sv13138 dot 26156 at savannah dot gnu dot org> <20070613-044302 dot sv13138 dot 42718 at savannah dot gnu dot org> <20070613-063711 dot sv13138 dot 86063 at savannah dot gnu dot org> <20070613-063821 dot sv13138 dot 28638 at savannah dot gnu dot org> <20070613-075056 dot sv13138 dot 72692 at savannah dot gnu dot org> <20070613-075935 dot sv13138 dot 27391 at savannah dot gnu dot org> <20070614-000207 dot sv13138 dot 96203 at savannah dot gnu dot org> <20070624-160912 dot sv13138 dot 20130 at savannah dot gnu dot org> <20070624154535 dot GK4668 at interface dot famille dot thibault dot fr>

Hi!

Re-submitting an oldie of Samuel's:

On Sun, 24 Jun 2007 17:45:35 +0200, Samuel Thibault <samuel.thibault@ens-lyon.org> wrote:
> - _start points on the first instruction, not on the elf header.
>   __executable_start does point on the elf header.

> --- sysdeps/mach/hurd/i386/init-first.c.orig	2007-06-23 19:27:14.000000000 +0000
> +++ sysdeps/mach/hurd/i386/init-first.c	2007-06-23 21:41:40.000000000 +0000
> @@ -116,14 +116,14 @@
>        /* We may need to see our own phdrs, e.g. for TLS setup.
>           Try the usual kludge to find the headers without help from
>  	 the exec server.  */
> -      extern const void _start;
> -      const ElfW(Ehdr) *const ehdr = &_start;
> +      extern const void __executable_start;
> +      const ElfW(Ehdr) *const ehdr = &__executable_start;
>        _dl_phdr = (ElfW(Phdr) *) ((const void *) ehdr + ehdr->e_phoff);
>        _dl_phnum = ehdr->e_phnum;
>        assert (ehdr->e_phentsize == sizeof (ElfW(Phdr)));

This is, as far as I can tell, the only such usage of _start in glibc.

OK to commit?

	* sysdeps/mach/hurd/i386/init-first.c (init1): Use
	__executable_start symbol intsead instead of _start.

diff --git sysdeps/mach/hurd/i386/init-first.c sysdeps/mach/hurd/i386/init-first.c
index fc3330c..7031ed4 100644
--- sysdeps/mach/hurd/i386/init-first.c
+++ sysdeps/mach/hurd/i386/init-first.c
@@ -125,8 +125,8 @@ init1 (int argc, char *arg0, ...)
           /* We may need to see our own phdrs, e.g. for TLS setup.
              Try the usual kludge to find the headers without help from
              the exec server.  */
-          extern const void _start;
-          const ElfW(Ehdr) *const ehdr = &_start;
+          extern const void __executable_start;
+          const ElfW(Ehdr) *const ehdr = &__executable_start;
           _dl_phdr = (const void *) ehdr + ehdr->e_phoff;
           _dl_phnum = ehdr->e_phnum;
           assert (ehdr->e_phentsize == sizeof (ElfW(Phdr)));


GrÃÃe,
 Thomas

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Follow-Ups:
- Re: __executable_start
  - From: Emilio Pozuelo Monfort
- Re: __executable_start (was: [bug #17644] glibc: support for TLS)
  - From: Roland McGrath

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