Description of problem:
X fails to launch for both "vesa" and "radeon" drivers on an "ATI Radeon X800". A backtrace is appended to Xorg.0.log. For the "radeon" driver, it reads:

  Backtrace:
  0: /usr/bin/X(xorg_backtrace+0x28) [0x45f3b8]
  1: /usr/bin/X [0x462d39]
  2: /lib64/libpthread.so.0 [0x7f888ee264c0]
  3: /lib64/libc.so.6 [0x7f888d660b26]
  4: /lib64/libc.so.6 [0x7f888d650150]
  5: /lib64/libc.so.6(__isoc99_vsscanf+0x65) [0x7f888d63f8f5]
  6: /lib64/libc.so.6(__isoc99_sscanf+0x88) [0x7f888d63f888]
  7: /usr/bin/X [0x474e8d]
  8: /usr/bin/X(InitOutput+0x52f) [0x470c0f]
  9: /usr/bin/X [0x4227aa]
  10: /lib64/libc.so.6(__libc_start_main+0xfd) [0x7f888d5f9b8d]
  11: /usr/bin/X [0x4224f9]

  Link map:
  0x7fff69aff000: (vdso)
  0x7f888ff26000: /usr/lib64/libxf86config.so.0
  0x7f888fd1f000: /usr/lib64/libpciaccess.so.0
  0x7f888faea000: /usr/lib64/libXfont.so.1
  0x7f888f8e8000: /usr/lib64/libXau.so.6
  0x7f888f6e1000: /usr/lib64/libfontenc.so.1
  0x7f888f485000: /usr/lib64/libpixman-1.so.0
  0x7f888f275000: /usr/lib64/libhal.so.1
  0x7f888f034000: /lib64/libdbus-1.so.3
  0x7f888ee17000: /lib64/libpthread.so.0
  0x7f888ec12000: /usr/lib64/libXdmcp.so.6
  0x7f888e9c0000: /usr/lib64/libssl.so.8
  0x7f888e636000: /usr/lib64/libcrypto.so.8
  0x7f888e432000: /lib64/libdl.so.2
  0x7f888e21d000: /lib64/libz.so.1
  0x7f888e003000: /lib64/libaudit.so.0
  0x7f888dde5000: /lib64/libselinux.so.1
  0x7f888db60000: /lib64/libm.so.6
  0x7f888d958000: /lib64/librt.so.1
  0x7f888d5db000: /lib64/libc.so.6
  0x7f888d340000: /usr/lib64/libfreetype.so.6
  0x7f888d13c000: /lib64/libcap.so.2
  0x7f8890138000: /lib64/ld-linux-x86-64.so.2
  0x7f888cf0d000: /lib64/libgssapi_krb5.so.2
  0x7f888cc50000: /lib64/libkrb5.so.3
  0x7f888ca4d000: /lib64/libcom_err.so.2
  0x7f888c821000: /lib64/libk5crypto.so.3
  0x7f888c61d000: /lib64/libattr.so.1
  0x7f888c414000: /lib64/libkrb5support.so.0
  0x7f888c212000: /lib64/libkeyutils.so.1
  0x7f888bff8000: /lib64/libresolv.so.2
  0x7f888bdd5000: /usr/lib64/xorg/modules/extensions/libextmod.so
  0x7f888bbd1000: /usr/lib64/xorg/modules/extensions/libdbe.so
  0x7f888b96a000: /usr/lib64/xorg/modules/extensions/libglx.so
  0x7f888b768000: /usr/lib64/xorg/modules/extensions/librecord.so
  0x7f888b55e000: /usr/lib64/xorg/modules/extensions/libdri.so
  0x7f888b354000: /usr/lib64/libdrm.so.2
  0x7f888b150000: /usr/lib64/xorg/modules/extensions/libdri2.so
  0x7f888ae5e000: /usr/lib64/xorg/modules/drivers/radeon_drv.so
  0x7f888ac5a000: /usr/lib64/libdrm_radeon.so.1
  0x7f888aa40000: /lib64/libgcc_s.so.1
  Segmentation fault at address (nil)

  Fatal server error:
  Caught signal 11 (Segmentation fault). Server aborting

Version-Release number of selected component (if applicable):
xorg-x11-server-Xorg-1.6.99-25.20090804.fc12.x86_64

How reproducible:
Always.

Steps to Reproduce:
1. Launch X.
  
Actual results:
X aborts instantaneously returning a backtrace.

Expected results:
X is launched successfully.

Additional info:
- Installed packages include:
  * kernel-2.6.31-0.125.rc5.git2.fc12.x86_64
  * xorg-x11-drv-ati-6.12.2-21.fc12.x86_64
  * xorg-x11-drv-vesa-2.2.1-1.fc12.x86_64
  * xorg-x11-server-Xorg-1.6.99-25.20090804.fc12.x86_64
- Reverting X packages to
  * xorg-x11-drv-ati-6.12.2-19.fc12.1.x86_64
  * xorg-x11-server-Xorg-1.6.99-23.20090724.fc12.x86_64
  allows to restore correct operation [KMS needs to be disabled though]