Originally filed in the Debian BTS,
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=413463

X crashes on start with the radeon driver, using version 6.6.3-5 of the Debian package. Using VESA or falling back to version 6.6.3-2 works ok.

Using a Radeon 9100
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon R200 QM [Radeon 9100]

X config is attached to the Debian bug, se above URL.

Backtrace of the crash,
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1210890560 (LWP 7460)]
0xb7c0aabe in RADEONValidateMergeModes (pScrn1=0x81ef390)
    at ../../src/radeon_modes.c:648
648	    if (pScrn->monitor->DDC) {
(gdb) #0  0xb7c0aabe in RADEONValidateMergeModes (pScrn1=0x81ef390)
    at ../../src/radeon_modes.c:648
#1  0xb7bf756f in RADEONPreInitModes (pScrn=0x81ef390, 
    pInt10=<value optimized out>) at ../../src/radeon_driver.c:2252
#2  0xb7bfa5c9 in RADEONPreInit (pScrn=0x81ef390, flags=<value optimized out>)
    at ../../src/radeon_driver.c:3187
#3  0x0809ff54 in InitOutput (pScreenInfo=0x81dc540, argc=11, argv=0xbfd3b294)
    at ../../../../hw/xfree86/common/xf86Init.c:601
#4  0x0806e35b in main (argc=11, argv=0xbfd3b294, envp=0xbfd3b2c4)
    at ../../dix/main.c:370
(gdb) Continuing.

Backtrace:
0: /usr/bin/Xorg.orig(xf86SigHandler+0x84) [0x80cc2a4]
1: [0xb7fc2420]
2: /usr/lib/xorg/modules/drivers//radeon_drv.so [0xb7bf756f]
3: /usr/lib/xorg/modules/drivers//radeon_drv.so(RADEONPreInit+0xb99) [0xb7bfa5c9]
4: /usr/bin/Xorg.orig(InitOutput+0x9c4) [0x809ff54]
5: /usr/bin/Xorg.orig(main+0x27b) [0x806e35b]
6: /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xc8) [0xb7ddaea8]
7: /usr/bin/Xorg.orig(FontFileCompleteXLFD+0xa5) [0x806d8a1]

Fatal server error:
Caught signal 11.  Server aborting


Program received signal SIGABRT, Aborted.
0xb7fc2410 in ?? ()
(gdb) The program is running.  Exit anyway? (y or n) [answered Y; input not from terminal]