Comment 5 for bug 311544

Running Xorg under gdb gives the following:

This is a pre-release version of the X server from The X.Org Foundation.
It is not supported in any way.
Bugs may be filed in the bugzilla at http://bugs.freedesktop.org/.
Select the "xorg" product for bugs you find in this release.
Before reporting bugs in pre-release versions please check the
latest version in the X.Org Foundation git repository.
See http://wiki.x.org/wiki/GitPage for git access instructions.

X.Org X Server 1.5.99.3
Release Date: (unreleased)
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.24-19-server i686 Ubuntu
Current Operating System: Linux ostrogoth 2.6.28-t23-200812261629 #26 PREEMPT Fri Dec 26 16:46:55 CET 2008 i686
Build Date: 17 December 2008 03:10:17AM
xorg-server 2:1.5.99.3-0ubuntu3 (<email address hidden>)
 Before reporting problems, check http://wiki.x.org
 to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
 (++) from command line, (!!) notice, (II) informational,
 (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Sun Dec 28 19:42:04 2008
(==) Using config file: "/etc/X11/xorg.conf"
[New Thread 0xb7a406c0 (LWP 7886)]
[tcsetpgrp failed in terminal_inferior: Operation not permitted]
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
    [10f] 320 x 200, 70Hz
    [112] 640 x 480, 60Hz, 72Hz, 75Hz, 85Hz, 100Hz
    [115] 800 x 600, 60Hz, 72Hz, 75Hz, 85Hz, 100Hz
    [118] 1024 x 768, 60Hz, 70Hz, 75Hz, 85Hz, 100Hz
    [11b] 1280 x 1024, 60Hz, 75Hz, 85Hz
    [11e] 640 x 400, 70Hz
    [124] 1600 x 1200, 60Hz, 75Hz, 85Hz
    [134] 320 x 240, 72Hz
    [13e] 1400 x 1050, 60Hz, 75Hz
    [144] 400 x 300, 72Hz
    [154] 512 x 384, 70Hz
    [175] 720 x 480, 75Hz
    [17f] 720 x 576, 75Hz

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb7b886c0 (LWP 30543)]
xf86_wrap_crtc_notify (screen=0x9ea5b70, new=0xb7b278c0 <dri_crtc_notify>) at ../../../../hw/xfree86/modes/xf86Crtc.c:2947
warning: Source file is more recent than executable.
2947 old = config->xf86_crtc_notify;

(gdb) thread apply all bt

Thread 1 (Thread 0xb7b886c0 (LWP 30543)):
#0 xf86_wrap_crtc_notify (screen=0x9ea5b70, new=0xb7b278c0 <dri_crtc_notify>)
    at ../../../../hw/xfree86/modes/xf86Crtc.c:2947
#1 0xb7b27821 in DRIFinishScreenInit (pScreen=0x9ea5b70) at ../../../../hw/xfree86/dri/dri.c:620
#2 0xb7af1dc0 in SAVAGEDRIFinishScreenInit (pScreen=0x9ea5b70) at ../../src/savage_dri.c:1071
#3 0xb7ae56f2 in SavageScreenInit (scrnIndex=0, pScreen=0x9ea5b70, argc=1, argv=0xbf9841c4)
    at ../../src/savage_driver.c:3646
#4 0x080711dd in AddScreen (pfnInit=0xb7ae4910 <SavageScreenInit>, argc=1, argv=0xbf9841c4) at ../../dix/main.c:688
#5 0x080adeb6 in InitOutput (pScreenInfo=0x81f3ee0, argc=1, argv=0xbf9841c4)
    at ../../../../hw/xfree86/common/xf86Init.c:1245
#6 0x080718d1 in main (argc=1, argv=0xbf9841c4, envp=0xbf9841cc) at ../../dix/main.c:309

So the segfault happens in xf86_wrap_crtc_notify () when it tries to assign something to old. However, old is optimized out by the compiler:

(gdb) p old
$1 = <value optimized out>
(gdb) p *old
Cannot access memory at address 0x0

Soooo... it seems my problems are caused by a compiler bug... I'll rebuild without optimizations and try again...