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..a7dc97bb080d311d04701093b6425b28cecc24f7 100644
--- a/base/cpu.cc
+++ b/base/cpu.cc
@@ -11,6 +11,16 @@
 #include "build/build_config.h"
 
 #if defined(ARCH_CPU_X86_FAMILY)
+#if defined(OS_LINUX)
+#include "base/file_util.h"
+#endif
+
+#if defined (OS_MACOSX)

[apatrick_chromium, 2013/03/06 19:19:21]

nit: space between "defined" and "("

+#include "base/version.h"

[apatrick_chromium, 2013/03/06 19:19:21]

#include "base/memory/scoped_ptr.h"

+#include <sys/param.h>
+#include <sys/sysctl.h>
+#endif
+

[apatrick_chromium, 2013/03/06 19:19:21]

#if defined(OS_WIN)
#include <windows.h>
#endif

 #if defined(_MSC_VER)
 #include <intrin.h>
 #endif
@@ -32,6 +42,7 @@ CPU::CPU()
     has_ssse3_(false),
     has_sse41_(false),
     has_sse42_(false),
+    has_avx_(false),
     cpu_vendor_("unknown") {
   Initialize();
 }
@@ -81,6 +92,56 @@ 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;

[apatrick_chromium, 2013/03/06 19:19:21]

Consider OSVERSIONINFOEX to get service pack version. See below.

+
+  if (!GetVersionEx(&version_info))

[apatrick_chromium, 2013/03/06 19:19:21]

You need to set version_info.dwOSVersionInfoSize to sizeof(version_info) before
calling this.

+    return false;
+
+  // Windows 7 SP1 added support for AVX.

[apatrick_chromium, 2013/03/06 19:19:21]

This tests for Windows 7 or later rather than Windows 7 SP1 or later. There's
code in base/win/windows_version.h to get the the service pack. Alternatively,
version_info.wServicePackMajor >= 1 when Windows version is 6.1.

+  return version_info.dwMajorVersion > 6 ||
+      version_info.dwMajorVersion == 6 &&
+      version_info.dwMinorVersion > 1;
+}
+#elif defined(OS_LINUX)
+bool OSHasAVXSupport() {
+  std::string buffer;
+  if (!file_util::ReadFileToString("/proc/cpuinfo", &buffer))

[DaleCurtis, 2013/03/06 18:32:37]

Is there a different way you can write this check? Doing this prevents base/cpu
from being used in the renderer side due to sandbox.

[apatrick_chromium, 2013/03/06 19:19:21]

First argument should be of type base::FilePath.

+    return false;
+
+  // Scan through /proc/cpuinfo to see if the kernel supports AVX.
+  return buffer.find("avx") != std::string::npos;
+}
+#elif  defined(OS_MACOSX)

[apatrick_chromium, 2013/03/06 19:19:21]

nit: two spaces between #elif and defined

+bool OSHasAVXSupport() {
+  size_t length;
+  char* kernel_version;
+  const static int mib[2] = {CTL_KERN, KERN_OSRELEASE};

[apatrick_chromium, 2013/03/06 19:19:21]

This is passed to sysctl so it can't be const.
http://docs.oracle.com/cd/E19048-01/chorus5/806-7021/6jfu393f0/index.html

+
+  if (sysctl(mib, 2, NULL, &length, NULL, 0) < 0)

[apatrick_chromium, 2013/03/06 19:19:21]

2 -> arraysize(mib)

+    return false;
+
+  scoped_ptr<char[]> buffer = new char[length];
+  if (!buffer)
+    return false;
+
+  if (sysctl(mib, 2, buffer, &length, NULL, 0) < 0)

[DaleCurtis, 2013/03/06 18:32:37]

Perhaps the same sandbox issue.

[apatrick_chromium, 2013/03/06 19:19:21]

buffer.get()
2 -> arraysize(mib)

+    return false;
+
+  base::Version kernel_version(buffer);

[apatrick_chromium, 2013/03/06 19:19:21]

kernel_version is declared twice. Also Version is in the global namespace rather
than base.

+  if (!kernel_version.IsValid())
+    return false;
+
+  // AVX support was added in 10.6.8, which has kernel 10.8.
+  return kernel_version.CompareTo(base::Version("10.8")) >= 0;
+}
+#else
+bool OSHasAVXSupport() {
+  return false;
+}
+#endif
 #endif  // ARCH_CPU_X86_FAMILY
 
 void CPU::Initialize() {
@@ -117,7 +178,7 @@ 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.