[x86] Disable AVX unless the operating system explicitly claims to support it.

src/ia32/assembler-ia32.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 28 matching lines @@
 #include <cstring>
 
 #if V8_TARGET_ARCH_IA32
 
 #if V8_OS_MACOSX
 #include <sys/sysctl.h>
 #endif
 
 #include "src/base/bits.h"
 #include "src/base/cpu.h"
-#if V8_OS_WIN
-#include "src/base/win32-headers.h"
-#endif
 #include "src/disassembler.h"
 #include "src/macro-assembler.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 
 // -----------------------------------------------------------------------------
 // Implementation of CpuFeatures
 
 namespace {
 
-bool EnableAVX() {
+bool OSHasAVXSupport() {
 #if V8_OS_MACOSX
   // Mac OS X up to 10.9 has a bug where AVX transitions were indeed being
   // caused by ISRs, so we detect that here and disable AVX in that case.
   char buffer[128];
   size_t buffer_size = arraysize(buffer);
-  int ctl_name[] = { CTL_KERN , KERN_OSRELEASE };
+  int ctl_name[] = {CTL_KERN, KERN_OSRELEASE};
   if (sysctl(ctl_name, 2, buffer, &buffer_size, nullptr, 0) != 0) {
     V8_Fatal(__FILE__, __LINE__, "V8 failed to get kernel version");
   }
   // The buffer now contains a string of the form XX.YY.ZZ, where
   // XX is the major kernel version component.
   char* period_pos = strchr(buffer, '.');
   DCHECK_NOT_NULL(period_pos);
   *period_pos = '\0';
   long kernel_version_major = strtol(buffer, nullptr, 10);  // NOLINT
   if (kernel_version_major <= 13) return false;
-#elif V8_OS_WIN
-  // The same problem seems to appear on Windows XP and Vista.
-  OSVERSIONINFOEX osvi;
-  DWORDLONG mask = 0;
-  memset(&osvi, 0, sizeof(osvi));
-  osvi.dwOSVersionInfoSize = sizeof(osvi);
-  osvi.dwMajorVersion = 6;
-  osvi.dwMinorVersion = 1;
-  VER_SET_CONDITION(mask, VER_MAJORVERSION, VER_GREATER_EQUAL);
-  VER_SET_CONDITION(mask, VER_MINORVERSION, VER_GREATER_EQUAL);
-  if (!VerifyVersionInfo(&osvi, VER_MAJORVERSION | VER_MINORVERSION, mask)) {
-    return false;
+#endif  // V8_OS_MACOSX
+  // Check whether OS claims to support AVX.
+  int flags = 0;
+#if V8_CC_GNU
+  // Check xgetbv; this uses a .byte sequence instead of the instruction
+  // directly because older assemblers do not include support for xgetbv and
+  // there is no easy way to conditionally compile based on the assembler used.
+  __asm__ __volatile__(".byte 0x0f, 0x01, 0xd0"
+                       : "=a"(flags)
+                       : "c"(0)
+                       : "%edx");
+#elif V8_CC_MSVC
+  __asm {
+    xor ecx, ecx  // ecx = 0
+    // Use the raw opcode for xgetbv for compatibility with older
+    // toolchains.
+        __asm _emit 0x0f __asm _emit 0x01 __asm _emit 0xd0

[Jakob Kummerow, 2015/01/27 09:07:34]

nit: indentation. (Or not, if clang-format doesn't like Tuesdays.)

+        mov flags, eax
   }
-#endif  // V8_OS_MACOSX
-  return FLAG_enable_avx;
+#endif
+  return (flags & 6) == 6;
 }
 
 }  // namespace
 
 
 void CpuFeatures::ProbeImpl(bool cross_compile) {
   base::CPU cpu;
   CHECK(cpu.has_sse2());  // SSE2 support is mandatory.
   CHECK(cpu.has_cmov());  // CMOV support is mandatory.
 
   // Only use statically determined features for cross compile (snapshot).
   if (cross_compile) return;
 
   if (cpu.has_sse41() && FLAG_enable_sse4_1) supported_ |= 1u << SSE4_1;
   if (cpu.has_sse3() && FLAG_enable_sse3) supported_ |= 1u << SSE3;
-  if (cpu.has_avx() && EnableAVX()) supported_ |= 1u << AVX;
-  if (cpu.has_fma3() && FLAG_enable_fma3) supported_ |= 1u << FMA3;
+  if (cpu.has_avx() && FLAG_enable_avx && cpu.has_osxsave() &&
+      OSHasAVXSupport()) {
+    supported_ |= 1u << AVX;
+  }
+  if (cpu.has_fma3() && FLAG_enable_fma3 && cpu.has_osxsave() &&
+      OSHasAVXSupport()) {
+    supported_ |= 1u << FMA3;
+  }
   if (strcmp(FLAG_mcpu, "auto") == 0) {
     if (cpu.is_atom()) supported_ |= 1u << ATOM;
   } else if (strcmp(FLAG_mcpu, "atom") == 0) {
     supported_ |= 1u << ATOM;
   }
 }
 
 
 void CpuFeatures::PrintTarget() { }
 void CpuFeatures::PrintFeatures() {
@@ skipping 2676 matching lines @@
     fprintf(coverage_log, "%s\n", file_line);
     fflush(coverage_log);
   }
 }
 
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32