Adding check for OS support to AVX

base/cpu.cc

Index: base/cpu.cc
diff --git a/base/cpu.cc b/base/cpu.cc
index d6976bab33b316aed50e3a133edf1a7e8a060a97..6191d1fc829dc4f42a6ac6cf64c2da7cc9bf28d7 100644
--- a/base/cpu.cc
+++ b/base/cpu.cc
@@ -11,6 +11,15 @@
 #include "build/build_config.h"
 
 #if defined(ARCH_CPU_X86_FAMILY)
+#if defined(OS_LINUX)
+#include <stdio.h>
+#endif
+
+#if defined (OS_MACOSX)
+#include <sys/param.h>
+#include <sys/sysctl.h>
+#endif
+
 #if defined(_MSC_VER)
 #include <intrin.h>
 #endif
@@ -32,6 +41,7 @@ CPU::CPU()
     has_ssse3_(false),
     has_sse41_(false),
     has_sse42_(false),
+    has_avx_(false),
     cpu_vendor_("unknown") {
   Initialize();
 }
@@ -81,6 +91,72 @@ void __cpuidex(int cpu_info[4], int info_type, int info_index) {
 
 #endif
 #endif  // _MSC_VER
+
+#if defined(OS_WIN)
+bool OSHasAVXSupport() {
+  OSVERSIONINFO version_info;
+
+  if (GetVersionEx(&version_info))

[apatrick_chromium, 2013/03/06 02:02:28]

Youu mean this?

if (!GetVersionEx(&version_info))

+    return false;
+
+  // Windows 7 SP1 added support for AVX.
+  return version_info.dwMajorVersion >= 6 && version_info.dwMinorVersion > 1;

[apatrick_chromium, 2013/03/06 02:02:28]

This won't work for 7.0 and 7.1 if the major version number ever gets bumped.
Also, it doesn't check for Windows 7 SP1, just Windows 8 and Windows Server
2012, right?

Check OSInfo in base/win/windows_version.h.

+}
+#elif defined(OS_LINUX)
+bool OSHasAVXSupport() {
+  FILE* f = fopen("/proc/cpuinfo", "r");

[apatrick_chromium, 2013/03/06 02:02:28]

I think you can use file_util::ReadFileToString here. Then there are no issues
with the fixed size buffer. Also, I think it will assert if it is called on a
thread that does not allow IO.

+  if (!f)
+    return false;
+
+  // Scan through /proc/cpuinfo to see if the kernel supports AVX.
+  char buffer[4096];
+  while (fgets(buffer, (int)sizeof(buffer), f)) {

[brettw, 2013/03/06 04:53:36]

Use C++ casts.

+    if (strncmp(buffer, "flags", sizeof(buffer))) {
+      if (strstr(buffer, "avx")) {

[apatrick_chromium, 2013/03/06 02:02:28]

Does /proc/cpuinfo reflect whether the OS has AVX or just the CPU?

+        fclose(f);
+        return true;
+      }
+    }
+  }
+
+  fclose(f);
+  return false;
+}
+#elif  defined(OS_MACOSX)
+bool OSHasAVXSupport() {
+  size_t length;
+  char* kernelVersion;

[apatrick_chromium, 2013/03/06 02:02:28]

nit: not chrome style

+  static int mib[2] = { CTL_KERN, KERN_OSRELEASE };
+
+  if (sysctl(mib, 2, NULL, &length, NULL, 0) < 0)
+    return false;
+
+  kernel_version = new char[length];

[apatrick_chromium, 2013/03/06 02:02:28]

scoped_ptr<char[]>

+  if (!kernel_version)
+    return false;
+
+  if (sysctl(mib, 2, kernel_version, &length, NULL, 0) < 0) {
+    delete [] kernel_version;

[apatrick_chromium, 2013/03/06 02:02:28]

not needed for scoped_ptr

+    return false;
+  }
+
+  int major, minor, patch_level;
+  if (sscanf(kernel_version, "%d.%d.%d", &major, &minor, &patch_level) != 3) {

[apatrick_chromium, 2013/03/06 02:02:28]

check base/version.h. It can deal with version numbers with a variable number of
components and has as IsOlderThan for comparisons.

+    if (sscanf(kernel_version, "%d.%d", &major, &minor) != 2) {
+      delete [] kernel_version;

[apatrick_chromium, 2013/03/06 02:02:28]

not needed for scoped_ptr

+      return false;
+    }
+  }
+  free(kernelVersion);

[apatrick_chromium, 2013/03/06 02:02:28]

kernelVersion is uninitialized

+
+  // AVX support was added in 10.6.8, which has kernel 10.8.
+  return major >= 10 && minor >= 8;

[apatrick_chromium, 2013/03/06 02:02:28]

This won't work for 11.0 through 11.7.

+}
+#else
+bool OSHasAVXSupport() {
+    return false;

[brettw, 2013/03/06 04:53:36]

indent.

+}
+#endif
 #endif  // ARCH_CPU_X86_FAMILY
 
 void CPU::Initialize() {
@@ -117,7 +193,7 @@ void CPU::Initialize() {
     has_ssse3_ = (cpu_info[2] & 0x00000200) != 0;
     has_sse41_ = (cpu_info[2] & 0x00080000) != 0;
     has_sse42_ = (cpu_info[2] & 0x00100000) != 0;
-    has_avx_ = (cpu_info[2] & 0x10000000) != 0;
+    has_avx_ = (cpu_info[2] & 0x10000000) != 0 && OSHasAVXSupport();
   }
 
   // Get the brand string of the cpu.