From 6577534a80c833bd310276f1e2bd3254271bb86d Mon Sep 17 00:00:00 2001 From: "Timothy B. Terriberry" Date: Tue, 28 Jun 2022 22:42:01 -0700 Subject: Work around a valgrind false-positive in CPUID. Valgrind versions prior to 3.17.0 assume that an uninitialized value in ECX causes the whole output of CPUID to be uninitialized, even though ECX is only "read" by CPUID for certain values of EAX. Work around that by guaranteeing that ECX is initialized. --- celt/x86/x86cpu.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/celt/x86/x86cpu.c b/celt/x86/x86cpu.c index accf0676..d95a9b94 100644 --- a/celt/x86/x86cpu.c +++ b/celt/x86/x86cpu.c @@ -68,7 +68,8 @@ static void cpuid(unsigned int CPUInfo[4], unsigned int InfoType) "=r" (CPUInfo[1]), "=c" (CPUInfo[2]), "=d" (CPUInfo[3]) : - "0" (InfoType) + /* We clear ECX to avoid a valgrind false-positive prior to v3.17.0. */ + "0" (InfoType), "2" (0) ); #else __asm__ __volatile__ ( @@ -77,12 +78,15 @@ static void cpuid(unsigned int CPUInfo[4], unsigned int InfoType) "=b" (CPUInfo[1]), "=c" (CPUInfo[2]), "=d" (CPUInfo[3]) : - "0" (InfoType) + /* We clear ECX to avoid a valgrind false-positive prior to v3.17.0. */ + "0" (InfoType), "2" (0) ); #endif #elif defined(CPU_INFO_BY_C) - if !(__get_cpuid(InfoType, &(CPUInfo[0]), &(CPUInfo[1]), &(CPUInfo[2]), &(CPUInfo[3]))) { - /* Our function cannot fail, but __get_cpuid can. + /* We use __get_cpuid_count to clear ECX to avoid a valgrind false-positive + prior to v3.17.0.*/ + if (!__get_cpuid_count(InfoType, 0, &(CPUInfo[0]), &(CPUInfo[1]), &(CPUInfo[2]), &(CPUInfo[3]))) { + /* Our function cannot fail, but __get_cpuid{_count} can. Returning all zeroes will effectively disable all SIMD, which is what we want on CPUs that don't support CPUID. */ CPUInfo[3] = CPUInfo[2] = CPUInfo[1] = CPUInfo[0] = 0; -- cgit v1.2.1