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Add a method to force the CPU flags

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Adds a method that forces the CPU flags. Useful when using libyuv inside
a sandboxed process which may not have access to the file system.

Bug: libyuv:787
Change-Id: I01f71e39a7301085d9de388eba930b4cac0fd7be
Reviewed-on: https://chromium-review.googlesource.com/972338
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>
This commit is contained in:
Jay Civelli 2018-03-22 10:38:22 -07:00 committed by Commit Bot
parent 6ecd76ae8d
commit fdad6299d6
3 changed files with 49 additions and 5 deletions
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25
include/libyuv/cpu_id.h
View File

@ -80,6 +80,31 @@ int ArmCpuCaps(const char* cpuinfo_name);
LIBYUV_API
int MaskCpuFlags(int enable_flags);
// Sets the CPU flags to |cpu_flags|, bypassing the detection code. |cpu_flags|
// should be a valid combination of the kCpuHas constants above and include
// kCpuInitialized. Use this method when running in a sandboxed process where
// the detection code might fail (as it might access /proc/cpuinfo). In such
// cases the cpu_info can be obtained from a non sandboxed process by calling
// InitCpuFlags() and passed to the sandboxed process (via command line
// parameters, IPC...) which can then call this method to initialize the CPU
// flags.
// Notes:
// - when specifying 0 for |cpu_flags|, the auto initialization is enabled
// again.
// - enabling CPU features that are not supported by the CPU will result in
// undefined behavior.
// TODO(fbarchard): consider writing a helper function that translates from
// other library CPU info to libyuv CPU info and add a .md doc that explains
// CPU detection.
static __inline void SetCpuFlags(int cpu_flags) {
LIBYUV_API extern int cpu_info_;
#ifdef __ATOMIC_RELAXED
__atomic_store_n(&cpu_info_, cpu_flags, __ATOMIC_RELAXED);
#else
cpu_info_ = cpu_flags;
#endif
}
// Low level cpuid for X86. Returns zeros on other CPUs.
// eax is the info type that you want.
// ecx is typically the cpu number, and should normally be zero.

6
source/cpu_id.cc
View File

@ -261,11 +261,7 @@ static SAFEBUFFERS int GetCpuFlags(void) {
LIBYUV_API
int MaskCpuFlags(int enable_flags) {
int cpu_info = GetCpuFlags() & enable_flags;
#ifdef __ATOMIC_RELAXED
__atomic_store_n(&cpu_info_, cpu_info, __ATOMIC_RELAXED);
#else
cpu_info_ = cpu_info;
#endif
SetCpuFlags(cpu_info);
return cpu_info;
}

23
unit_test/cpu_test.cc
View File

@ -158,4 +158,27 @@ TEST_F(LibYUVBaseTest, TestLinuxNeon) {
#endif
}
TEST_F(LibYUVBaseTest, TestSetCpuFlags) {
// Reset any masked flags that may have been set so auto init is enabled.
MaskCpuFlags(0);
int original_cpu_flags = TestCpuFlag(-1);
// Test setting different CPU configurations.
int cpu_flags = kCpuHasARM | kCpuHasNEON | kCpuInitialized;
SetCpuFlags(cpu_flags);
EXPECT_EQ(cpu_flags, TestCpuFlag(-1));
cpu_flags = kCpuHasX86 | kCpuInitialized;
SetCpuFlags(cpu_flags);
EXPECT_EQ(cpu_flags, TestCpuFlag(-1));
// Test that setting 0 turns auto-init back on.
SetCpuFlags(0);
EXPECT_EQ(original_cpu_flags, TestCpuFlag(-1));
// Restore the CPU flag mask.
MaskCpuFlags(benchmark_cpu_info_);
}
} // namespace libyuv