Re: %gs:0x14

[Neill Miller]

On Tue, 14 Nov 2006 17:57:50 +0100
Thomas Schwinge <tschwinge@gnu.org> wrote:

Oops, that was on PPC.  Let me try this again ;-)

Note that while it's an AMD 64 chip, it's running in full 32-bit mode with no 
64 bit anything.  Hope that helps.

> #v+
> $ echo 'void f (void) { volatile char a[8]; a[3]; }' | gcc -S -x c -O2 
> -fstack-protector - -o -; uname -a; /lib/libc-*.so
> #v-

boiler ~ # /lib/libc.so.6 
GNU C Library stable release version 2.5, by Roland McGrath et al.
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.1.1 (Gentoo 4.1.1-r1).
Compiled on a Linux 2.6.17 system on 2006-10-30.
Available extensions:
        The C stubs add-on version 2.1.2.
        crypt add-on version 2.1 by Michael Glad and others
        Gentoo patchset 1.2
        GNU Libidn by Simon Josefsson
        GNU libio by Per Bothner
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
        Native POSIX Threads Library by Ulrich Drepper et al
        Support for some architectures added on, not maintained in glibc core.
        BIND-8.2.3-T5B
Thread-local storage support included.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.
boiler ~ # gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/gcc-4.1.1-r1/work/gcc-4.1.1/configure 
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.1 
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.1/include 
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.1 
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.1/man 
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.1/info 
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.1/include/g++-v4 
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec 
--enable-nls --without-included-gettext --with-system-zlib --disable-checking 
--disable-werror --disable-libunwind-exceptions --disable-multilib 
--disable-libmudflap --disable-libssp --disable-libgcj 
--enable-languages=c,c++,fortran --enable-shared --enable-threads=posix 
--enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.1 (Gentoo 4.1.1-r1)
boiler ~ # echo 'void f (void) { volatile char a[8]; a[3]; }' | gcc -S -x c -O2 
-fstack-protector - -o -; uname -a; /lib/libc-*.so
        .file   ""
        .text
        .p2align 4,,15
.globl f
        .type   f, @function
f:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        movl    %gs:20, %eax
        movl    %eax, -4(%ebp)
        xorl    %eax, %eax
        movzbl  -9(%ebp), %eax
        movl    -4(%ebp), %eax
        xorl    %gs:20, %eax
        jne     .L5
        leave
        ret
.L5:
        call    __stack_chk_fail
        .size   f, .-f
        .ident  "GCC: (GNU) 4.1.1 (Gentoo 4.1.1-r1)"
        .section        .note.GNU-stack,"",@progbits
Linux boiler.chaos.net 2.6.18 #1 PREEMPT Sat Oct 7 15:31:26 CDT 2006 i686 AMD 
Athlon(tm) 64 Processor 3200+ AuthenticAMD GNU/Linux
GNU C Library stable release version 2.5, by Roland McGrath et al.
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.1.1 (Gentoo 4.1.1-r1).
Compiled on a Linux 2.6.17 system on 2006-10-30.
Available extensions:
        The C stubs add-on version 2.1.2.
        crypt add-on version 2.1 by Michael Glad and others
        Gentoo patchset 1.2
        GNU Libidn by Simon Josefsson
        GNU libio by Per Bothner
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
        Native POSIX Threads Library by Ulrich Drepper et al
        Support for some architectures added on, not maintained in glibc core.
        BIND-8.2.3-T5B
Thread-local storage support included.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.

-Neill.
(IRC: __sempai)