From b3d17c1cf29ac8cd6b2fcd1db7d824e4af9ea505 Mon Sep 17 00:00:00 2001 From: Carlos O'Donell Date: Mon, 17 Oct 2016 19:35:34 -0400 Subject: Bug 20689: Fix FMA and AVX2 detection on Intel In the Intel Architecture Instruction Set Extensions Programming reference the recommended way to test for FMA in section '2.2.1 Detection of FMA' is: "Application Software must identify that hardware supports AVX as explained in ... after that it must also detect support for FMA..." We don't do that in glibc. We use osxsave to detect the use of xgetbv, and after that we check for AVX and FMA orthogonally. It is conceivable that you could have the AVX bit clear and the FMA bit in an undefined state. This commit fixes FMA and AVX2 detection to depend on usable AVX as required by the recommended Intel sequences. v1: https://www.sourceware.org/ml/libc-alpha/2016-10/msg00241.html v2: https://www.sourceware.org/ml/libc-alpha/2016-10/msg00265.html --- sysdeps/x86/cpu-features.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) (limited to 'sysdeps') diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index 11b9af2231..e228a76c40 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -60,12 +60,20 @@ get_common_indeces (struct cpu_features *cpu_features, { /* Determine if AVX is usable. */ if (CPU_FEATURES_CPU_P (cpu_features, AVX)) - cpu_features->feature[index_arch_AVX_Usable] - |= bit_arch_AVX_Usable; - /* Determine if AVX2 is usable. */ - if (CPU_FEATURES_CPU_P (cpu_features, AVX2)) - cpu_features->feature[index_arch_AVX2_Usable] - |= bit_arch_AVX2_Usable; + { + cpu_features->feature[index_arch_AVX_Usable] + |= bit_arch_AVX_Usable; + /* The following features depend on AVX being usable. */ + /* Determine if AVX2 is usable. */ + if (CPU_FEATURES_CPU_P (cpu_features, AVX2)) + cpu_features->feature[index_arch_AVX2_Usable] + |= bit_arch_AVX2_Usable; + /* Determine if FMA is usable. */ + if (CPU_FEATURES_CPU_P (cpu_features, FMA)) + cpu_features->feature[index_arch_FMA_Usable] + |= bit_arch_FMA_Usable; + } + /* Check if OPMASK state, upper 256-bit of ZMM0-ZMM15 and ZMM16-ZMM31 state are enabled. */ if ((xcrlow & (bit_Opmask_state | bit_ZMM0_15_state @@ -83,10 +91,6 @@ get_common_indeces (struct cpu_features *cpu_features, |= bit_arch_AVX512DQ_Usable; } } - /* Determine if FMA is usable. */ - if (CPU_FEATURES_CPU_P (cpu_features, FMA)) - cpu_features->feature[index_arch_FMA_Usable] - |= bit_arch_FMA_Usable; } } } -- cgit 1.4.1