今天研究下cpufeatures库，它是一个轻量级的展示CPU特性的模块，调用者在运行时候可以根据这个库提供的简单接口获取到目标机的CPU架构和特性。
一、代码路径：
$NDK_ROOT/sources/android/cpufeatures
二、主要功能
1. 获取目标机CPU架构，涵盖了android可能运行所有CPU架构，设置ABI的时候可以参考
extern AndroidCpuFamily android_getCpuFamily(void);
typedef enum {
ANDROID_CPU_FAMILY_UNKNOWN = 0,
ANDROID_CPU_FAMILY_ARM,
ANDROID_CPU_FAMILY_X86,
ANDROID_CPU_FAMILY_MIPS,
ANDROID_CPU_FAMILY_ARM64,
ANDROID_CPU_FAMILY_X86_64,
ANDROID_CPU_FAMILY_MIPS64,
ANDROID_CPU_FAMILY_MAX /* do not remove */
} AndroidCpuFamily;
2. 获取CPU性能，不同的CPU架构有不同的性能，例如arm支持的指令集有VFPV2、ARMv7-A、NEON
extern uint64_t android_getCpuFeatures(void); // 注意：此方法32bit和64bit arm内核的返回不对等
enum {
ANDROID_CPU_ARM_FEATURE_ARMv7 = (1 << 0),
ANDROID_CPU_ARM_FEATURE_VFPv3 = (1 << 1),
ANDROID_CPU_ARM_FEATURE_NEON = (1 << 2),
ANDROID_CPU_ARM_FEATURE_LDREX_STREX = (1 << 3),
ANDROID_CPU_ARM_FEATURE_VFPv2 = (1 << 4),
ANDROID_CPU_ARM_FEATURE_VFP_D32 = (1 << 5),
ANDROID_CPU_ARM_FEATURE_VFP_FP16 = (1 << 6),
ANDROID_CPU_ARM_FEATURE_VFP_FMA = (1 << 7),
ANDROID_CPU_ARM_FEATURE_NEON_FMA = (1 << 8),
ANDROID_CPU_ARM_FEATURE_IDIV_ARM = (1 << 9),
ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2 = (1 << 10),
ANDROID_CPU_ARM_FEATURE_iWMMXt = (1 << 11),
ANDROID_CPU_ARM_FEATURE_AES = (1 << 12),
ANDROID_CPU_ARM_FEATURE_PMULL = (1 << 13),
ANDROID_CPU_ARM_FEATURE_SHA1 = (1 << 14),
ANDROID_CPU_ARM_FEATURE_SHA2 = (1 << 15),
ANDROID_CPU_ARM_FEATURE_CRC32 = (1 << 16),
};
要支持不同的指令集，要添加对应的编译选项，详细见附录
-mfpu=neon // 支持neon指令集
3. 获取CPU个数
extern int android_getCpuCount(void);
4. 设置CPU个数，沙盒模拟测试
extern int android_setCpu(int cpu_count, uint64_t cpu_features);
extern uint32_t android_getCpuIdArm(void);
extern int android_setCpuArm(int cpu_count, uint64_t cpu_features, uint32_t cpu_id)；
三、 使用举例
1. 以下展示了一个筛选armv7并支持neon指令集的代码
#include <cpu-features.h>
AndroidCUPFamily family = android_getCpuFamily();
if (family != ANDROID_CPU_FAMILY_ARM) { printf("Not an ARM CPU ! "); return; }
uint64_t features = android_getCpuFeatures();
if ((features & ANDROID_CPU_ARM_FEATURE_ARMv7) == 0)
{
printf("Not an ARMv7 CPU ! ")
return;
}
if ((features & ANDROID_CPU_ARM_FEATURE_NEON) == 0)
{
printf("CPU doesn't support NEON ! ");
return;
}
2. 工程引入
# build cpufeatures as a static lib add_library(cpufeatures STATIC ${ANDROID_NDK}/sources/android/cpufeatures/cpu-features.c)
# include directories target_include_directories(hello-neon PRIVATE ${ANDROID_NDK}/sources/android/cpufeatures)
# link target_link_libraries(hello-neon cpufeatures)
附录：
/* * Copyright (C) 2010 The Android Open Source Project * 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. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #ifndef CPU_FEATURES_H #define CPU_FEATURES_H #include <sys/cdefs.h> #include <stdint.h> __BEGIN_DECLS /* A list of valid values returned by android_getCpuFamily(). * They describe the CPU Architecture of the current process. */ typedef enum { ANDROID_CPU_FAMILY_UNKNOWN = 0, ANDROID_CPU_FAMILY_ARM, ANDROID_CPU_FAMILY_X86, ANDROID_CPU_FAMILY_MIPS, ANDROID_CPU_FAMILY_ARM64, ANDROID_CPU_FAMILY_X86_64, ANDROID_CPU_FAMILY_MIPS64, ANDROID_CPU_FAMILY_MAX /* do not remove */ } AndroidCpuFamily; /* Return the CPU family of the current process. * * Note that this matches the bitness of the current process. I.e. when * running a 32-bit binary on a 64-bit capable CPU, this will return the * 32-bit CPU family value. */ extern AndroidCpuFamily android_getCpuFamily(void); /* Return a bitmap describing a set of optional CPU features that are * supported by the current device's CPU. The exact bit-flags returned * depend on the value returned by android_getCpuFamily(). See the * documentation for the ANDROID_CPU_*_FEATURE_* flags below for details. */ extern uint64_t android_getCpuFeatures(void); /* The list of feature flags for ANDROID_CPU_FAMILY_ARM that can be * recognized by the library (see note below for 64-bit ARM). Value details * are: * * VFPv2: * CPU supports the VFPv2 instruction set. Many, but not all, ARMv6 CPUs * support these instructions. VFPv2 is a subset of VFPv3 so this will * be set whenever VFPv3 is set too. * * ARMv7: * CPU supports the ARMv7-A basic instruction set. * This feature is mandated by the 'armeabi-v7a' ABI. * * VFPv3: * CPU supports the VFPv3-D16 instruction set, providing hardware FPU * support for single and double precision floating point registers. * Note that only 16 FPU registers are available by default, unless * the D32 bit is set too. This feature is also mandated by the * 'armeabi-v7a' ABI. * * VFP_D32: * CPU VFP optional extension that provides 32 FPU registers, * instead of 16. Note that ARM mandates this feature is the 'NEON' * feature is implemented by the CPU. * * NEON: * CPU FPU supports "ARM Advanced SIMD" instructions, also known as * NEON. Note that this mandates the VFP_D32 feature as well, per the * ARM Architecture specification. * * VFP_FP16: * Half-width floating precision VFP extension. If set, the CPU * supports instructions to perform floating-point operations on * 16-bit registers. This is part of the VFPv4 specification, but * not mandated by any Android ABI. * * VFP_FMA: * Fused multiply-accumulate VFP instructions extension. Also part of * the VFPv4 specification, but not mandated by any Android ABI. * * NEON_FMA: * Fused multiply-accumulate NEON instructions extension. Optional * extension from the VFPv4 specification, but not mandated by any * Android ABI. * * IDIV_ARM: * Integer division available in ARM mode. Only available * on recent CPUs (e.g. Cortex-A15). * * IDIV_THUMB2: * Integer division available in Thumb-2 mode. Only available * on recent CPUs (e.g. Cortex-A15). * * iWMMXt: * Optional extension that adds MMX registers and operations to an * ARM CPU. This is only available on a few XScale-based CPU designs * sold by Marvell. Pretty rare in practice. * * AES: * CPU supports AES instructions. These instructions are only * available for 32-bit applications running on ARMv8 CPU. * * CRC32: * CPU supports CRC32 instructions. These instructions are only * available for 32-bit applications running on ARMv8 CPU. * * SHA2: * CPU supports SHA2 instructions. These instructions are only * available for 32-bit applications running on ARMv8 CPU. * * SHA1: * CPU supports SHA1 instructions. These instructions are only * available for 32-bit applications running on ARMv8 CPU. * * PMULL: * CPU supports 64-bit PMULL and PMULL2 instructions. These * instructions are only available for 32-bit applications * running on ARMv8 CPU. * * If you want to tell the compiler to generate code that targets one of * the feature set above, you should probably use one of the following * flags (for more details, see technical note at the end of this file): * * -mfpu=vfp * -mfpu=vfpv2 * These are equivalent and tell GCC to use VFPv2 instructions for * floating-point operations. Use this if you want your code to * run on *some* ARMv6 devices, and any ARMv7-A device supported * by Android. * * Generated code requires VFPv2 feature. * * -mfpu=vfpv3-d16 * Tell GCC to use VFPv3 instructions (using only 16 FPU registers). * This should be generic code that runs on any CPU that supports the * 'armeabi-v7a' Android ABI. Note that no ARMv6 CPU supports this. * * Generated code requires VFPv3 feature. * * -mfpu=vfpv3 * Tell GCC to use VFPv3 instructions with 32 FPU registers. * Generated code requires VFPv3|VFP_D32 features. * * -mfpu=neon * Tell GCC to use VFPv3 instructions with 32 FPU registers, and * also support NEON intrinsics (see <arm_neon.h>). * Generated code requires VFPv3|VFP_D32|NEON features. * * -mfpu=vfpv4-d16 * Generated code requires VFPv3|VFP_FP16|VFP_FMA features. * * -mfpu=vfpv4 * Generated code requires VFPv3|VFP_FP16|VFP_FMA|VFP_D32 features. * * -mfpu=neon-vfpv4 * Generated code requires VFPv3|VFP_FP16|VFP_FMA|VFP_D32|NEON|NEON_FMA * features. * * -mcpu=cortex-a7 * -mcpu=cortex-a15 * Generated code requires VFPv3|VFP_FP16|VFP_FMA|VFP_D32| * NEON|NEON_FMA|IDIV_ARM|IDIV_THUMB2 * This flag implies -mfpu=neon-vfpv4. * * -mcpu=iwmmxt * Allows the use of iWMMXt instrinsics with GCC. * * IMPORTANT NOTE: These flags should only be tested when * android_getCpuFamily() returns ANDROID_CPU_FAMILY_ARM, i.e. this is a * 32-bit process. * * When running a 64-bit ARM process on an ARMv8 CPU, * android_getCpuFeatures() will return a different set of bitflags */ enum { ANDROID_CPU_ARM_FEATURE_ARMv7 = (1 << 0), ANDROID_CPU_ARM_FEATURE_VFPv3 = (1 << 1), ANDROID_CPU_ARM_FEATURE_NEON = (1 << 2), ANDROID_CPU_ARM_FEATURE_LDREX_STREX = (1 << 3), ANDROID_CPU_ARM_FEATURE_VFPv2 = (1 << 4), ANDROID_CPU_ARM_FEATURE_VFP_D32 = (1 << 5), ANDROID_CPU_ARM_FEATURE_VFP_FP16 = (1 << 6), ANDROID_CPU_ARM_FEATURE_VFP_FMA = (1 << 7), ANDROID_CPU_ARM_FEATURE_NEON_FMA = (1 << 8), ANDROID_CPU_ARM_FEATURE_IDIV_ARM = (1 << 9), ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2 = (1 << 10), ANDROID_CPU_ARM_FEATURE_iWMMXt = (1 << 11), ANDROID_CPU_ARM_FEATURE_AES = (1 << 12), ANDROID_CPU_ARM_FEATURE_PMULL = (1 << 13), ANDROID_CPU_ARM_FEATURE_SHA1 = (1 << 14), ANDROID_CPU_ARM_FEATURE_SHA2 = (1 << 15), ANDROID_CPU_ARM_FEATURE_CRC32 = (1 << 16), }; /* The bit flags corresponding to the output of android_getCpuFeatures() * when android_getCpuFamily() returns ANDROID_CPU_FAMILY_ARM64. Value details * are: * * FP: * CPU has Floating-point unit. * * ASIMD: * CPU has Advanced SIMD unit. * * AES: * CPU supports AES instructions. * * CRC32: * CPU supports CRC32 instructions. * * SHA2: * CPU supports SHA2 instructions. * * SHA1: * CPU supports SHA1 instructions. * * PMULL: * CPU supports 64-bit PMULL and PMULL2 instructions. */ enum { ANDROID_CPU_ARM64_FEATURE_FP = (1 << 0), ANDROID_CPU_ARM64_FEATURE_ASIMD = (1 << 1), ANDROID_CPU_ARM64_FEATURE_AES = (1 << 2), ANDROID_CPU_ARM64_FEATURE_PMULL = (1 << 3), ANDROID_CPU_ARM64_FEATURE_SHA1 = (1 << 4), ANDROID_CPU_ARM64_FEATURE_SHA2 = (1 << 5), ANDROID_CPU_ARM64_FEATURE_CRC32 = (1 << 6), }; /* The bit flags corresponding to the output of android_getCpuFeatures() * when android_getCpuFamily() returns ANDROID_CPU_FAMILY_X86 or * ANDROID_CPU_FAMILY_X86_64. */ enum { ANDROID_CPU_X86_FEATURE_SSSE3 = (1 << 0), ANDROID_CPU_X86_FEATURE_POPCNT = (1 << 1), ANDROID_CPU_X86_FEATURE_MOVBE = (1 << 2), ANDROID_CPU_X86_FEATURE_SSE4_1 = (1 << 3), ANDROID_CPU_X86_FEATURE_SSE4_2 = (1 << 4), ANDROID_CPU_X86_FEATURE_AES_NI = (1 << 5), ANDROID_CPU_X86_FEATURE_AVX = (1 << 6), ANDROID_CPU_X86_FEATURE_RDRAND = (1 << 7), ANDROID_CPU_X86_FEATURE_AVX2 = (1 << 8), ANDROID_CPU_X86_FEATURE_SHA_NI = (1 << 9), }; /* The bit flags corresponding to the output of android_getCpuFeatures() * when android_getCpuFamily() returns ANDROID_CPU_FAMILY_MIPS * or ANDROID_CPU_FAMILY_MIPS64. Values are: * * R6: * CPU executes MIPS Release 6 instructions natively, and * supports obsoleted R1..R5 instructions only via kernel traps. * * MSA: * CPU supports Mips SIMD Architecture instructions. */ enum { ANDROID_CPU_MIPS_FEATURE_R6 = (1 << 0), ANDROID_CPU_MIPS_FEATURE_MSA = (1 << 1), }; /* Return the number of CPU cores detected on this device. */ extern int android_getCpuCount(void); /* The following is used to force the CPU count and features * mask in sandboxed processes. Under 4.1 and higher, these processes * cannot access /proc, which is the only way to get information from * the kernel about the current hardware (at least on ARM). * * It _must_ be called only once, and before any android_getCpuXXX * function, any other case will fail. * * This function return 1 on success, and 0 on failure. */ extern int android_setCpu(int cpu_count, uint64_t cpu_features); #ifdef __arm__ /* Retrieve the ARM 32-bit CPUID value from the kernel. * Note that this cannot work on sandboxed processes under 4.1 and * higher, unless you called android_setCpuArm() before. */ extern uint32_t android_getCpuIdArm(void); /* An ARM-specific variant of android_setCpu() that also allows you * to set the ARM CPUID field. */ extern int android_setCpuArm(int cpu_count, uint64_t cpu_features, uint32_t cpu_id); #endif __END_DECLS #endif /* CPU_FEATURES_H */