[Bug 1096323] Re: valgrind claims to support 3dnow! in cpuid, but doesn't

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On 2012-01-15T10:36:17+00:00 Reimar Döffinger wrote:

Created attachment 67842
Remove 3dnow support bits from CPUID

Currently the CPUID values for this are based on a real CPU.
Unfortunately, it is an AMD CPU.
This means that CPUID claims to support 3DNOW while it actually doesn't.
As a result, any program doing audio decoding with FFmpeg crashes in valgrind in x86_64 mode.
Attached patch just hacks the CPUID a bit to remove the 3DNOW flags.
That is not perfect since it now matches no real CPU but claiming to support a feature that will certainly crash is surely worse.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/valgrind/+bug/1096323/comments/0

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On 2012-02-20T20:41:09+00:00 Reimar Döffinger wrote:

Sorry to be impatient, but I'd appreciate if someone could have a look.
This is a really old issue I got finally annoyed enough about to debug
(as a MPlayer/FFmpeg developer using an AMD CPU it is really annoying
when valgrind crashes the program you're debugging half the time).

Reply at:
https://bugs.launchpad.net/ubuntu/+source/valgrind/+bug/1096323/comments/1

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On 2012-02-21T08:59:11+00:00 Jseward wrote:

Committed w/ extra comments, r2259.  Thanks.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/valgrind/+bug/1096323/comments/2


** Changed in: valgrind
       Status: Unknown => Fix Released

** Changed in: valgrind
   Importance: Unknown => Medium

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https://bugs.launchpad.net/bugs/1096323

Title:
  valgrind claims to support 3dnow! in cpuid, but doesn't

Status in Valgrind:
  Fix Released
Status in “valgrind” package in Ubuntu:
  New

Bug description:
  See https://bugs.kde.org/show_bug.cgi?id=291568 - on AMD CPUs,
  valgrind exposes a cpuid that shows 3dnow support, however valgrind
  doesn't actually support those instructions.

  This results in IR decoding errors when using valgrind on ffmpeg-
  related apps (in my case, mythtv).

  I get:

  vex amd64->IR: unhandled instruction bytes: 0xF 0xF 0xC1 0xBF 0xF 0xF
  0xD3 0xBF

  (In this case, this is the PAVGUSB instruction)

  The "fix" is in https://bugs.kde.org/show_bug.cgi?id=291568, which
  masks out the appropriate CPUID bit so that 3dnow isn't claimed as
  present. A bit hackish, but since its upstream....

  Ubuntu 12.04, valgrind 1:3.7.0-0ubuntu3

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