Bug 68297

Summary:	Mesa tries to detect AVX support and fails horribly
Product:	Mesa	Reporter:	Pierre Bourdon <delroth>
Component:	Other	Assignee:	mesa-dev
Status:	RESOLVED INVALID	QA Contact:
Severity:	major
Priority:	medium
Version:	git
Hardware:	x86-64 (AMD64)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:

Description Pierre Bourdon 2013-08-20 00:03:23 UTC

src/gallium/auxiliary/util/u_cpu_detect.c:         util_cpu_caps.has_avx    = ((regs2[2] >> 28) & 1) && // AVX

This is wrong. To check for AVX support, you need to:
1. Check if the AVX bit is set in cpuid (DONE)
2. Check if the XSAVE bit is set in cpuid (NOT DONE)
3. Check if xgetbv with ecx=0 & XFEATURE_ENABLED_MASK == XFEATURE_ENABLED_MASK (NOT DONE)

See, for example:
https://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86Subtarget.cpp?r1=180991&r2=180990&pathrev=180991
https://code.google.com/p/dolphin-emu/source/detail?r=377202b9f6154ae56c5b2f0a45e235ceaeb6da9c

Intel have some reference material about that but software.intel.com seems to be down at the moment.

When trying to run llvmpipe on a machine with hardware AVX support but no kernel support for it, it currently SIGILLs.

Comment 1 Pierre Bourdon 2013-08-20 00:05:23 UTC

Nevermind, I was using a non Git version, looking at a recent Git checkout it seems to have been fixed on Jul 23.

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