[Bug 1247607] Re: Libdrm compiled with gcc 4.8 makes card hang on resume from s2disk

[Launchpad Bug Tracker]

** Branch linked: lp:ubuntu/saucy-proposed/libdrm

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https://bugs.launchpad.net/bugs/1247607

Title:
  Libdrm compiled with gcc 4.8 makes card hang on resume from s2disk

Status in The GNU Compiler Collection:
  New
Status in Accelerated Xorg driver for nVidia cards:
  Fix Released
Status in “libdrm” package in Ubuntu:
  Fix Released
Status in “libdrm” source package in Saucy:
  Fix Committed

Bug description:
  [Impact] 
   * Relocations on nv04-nv4f are completely broken, any kind of memory stress will result in userspace failure.

  [Test Case]
   * Suspend on a system with an affected nvidia card.
   * Resume should complete without any errors in FIFO.
   * Other test is to run max-texture-size from piglit, system should survive.
   * For m-a same change: confirm libdrm-dev:amd64 and libdrm-dev:i386 coinstall.

  [Regression Potential] 
   * Original bug report was caused by undefined behavior in gcc:
     - *push->cur++ = pushbuf_krel(push) 
     - pushbuf_krel uses (push->cur - push->bgn) to calculate offset.
     - It's undefined whether push->cur is incremented before calling pushbuf_krel or not.
     - New gcc changed the order, causing the bug.
     - Fixed by calling push->cur++ in a separate statement.
   * Bug reports will be watched for any new problems that may pop up.

  [Original bug report]
  My initial bugreport was here: https://bugs.freedesktop.org/show_bug.cgi?id=71116

  - Recompiling libdrm with gcc 4.7 fixed the bug.

  Upstream GCC mail thread here: http://gcc.gnu.org/ml/gcc-
  help/2013-07/msg00103.html

  This was fixed thanks to Emil Velikov from the nouveau project.

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