NDK CPU Features
薛宇
Android NDK CPU Features detection library:
-------------------------------------------
This NDK provides a small library named "cpufeatures" that can be used at
runtime to detect the target device's CPU family and the optional features
it supports.
Usage:
------
The library is available as an import module. To use it, you must:
To use it, you must:
* List 'cpufeatures' in your list of static library dependencies, as in:
LOCAL_STATIC_LIBRARIES := cpufeatures
* At the end of your Android.mk, import the 'android/cpufeatures' module,
as in:
$(call import-module,android/cpufeatures)
* In your source code, include the header named <cpu-features.h>
Here is a simple example:
<project-path>/jni/Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := <your-module-name>
LOCAL_SRC_FILES := <your-source-files>
LOCAL_STATIC_LIBRARIES := cpufeatures
include $(BUILD_SHARED_LIBRARY)
$(call import-module,android/cpufeatures)
Features:
---------
Two functions are provided for now:
AndroidCpuFamily android_getCpuFamily();
Returns the target device's CPU Family as an enum. For now, the only
supported family is ANDROID_CPU_FAMILY_ARM.
uint64_t android_getCpuFeatures();
Returns the set of optional features supported by the device's CPU.
The result is a set of bit-flags, each corresponding to one CPU
Family-specific optional feature.
Currently, only the following flags are defined, for the ARM CPU Family:
ANDROID_CPU_ARM_FEATURE_VFPv2
Indicates that the device's CPU supports VFPv2 instruction set.
Most ARMv6 CPUs support these.
ANDROID_CPU_ARM_FEATURE_ARMv7
Indicates that the device's CPU supports the ARMv7-A instruction
set as supported by the "armeabi-v7a" abi (see CPU-ARCH-ABIS.html).
This corresponds to Thumb-2 and VFPv3-D16 instructions.
ANDROID_CPU_ARM_FEATURE_VFPv3
Indicates that the device's CPU supports the VFPv3 hardware FPU
instruction set extension. Due to the definition of 'armeabi-v7a',
this will always be the case if ANDROID_CPU_ARM_FEATURE_ARMv7 is
returned.
Note that this corresponds to the minimum profile VFPv3-D16 that
_only_ provides 16 hardware double-precision FP registers.
ANDROID_CPU_ARM_FEATURE_VFP_D32
Indicates that the device's CPU supports 32 hardware double-precision
FP registers instead of 16. Note that there are still only 32 single-
precision registers mapped to the same register banks.
ANDROID_CPU_ARM_FEATURE_NEON
Indicates that the device's CPU supports the ARM Advanced SIMD
(a.k.a. NEON) vector instruction set extension. Note that ARM
mandates that such CPUs also implement VFPv3-D32, which provides
32 hardware FP registers (shared with the NEON unit).
ANDROID_CPU_ARM_FEATURE_VFP_FP16
Indicates that the device's CPU supports instructions to perform
floating-point operations on 16-bit registers. This is part of the
VFPv4 specification.
ANDROID_CPU_ARM_FEATURE_VFP_FMA
Indicates that the device's CPU supports fused multiply-accumulate
VFP instructions extension. Also part of the VFPv4 specification.
ANDROID_CPU_ARM_FEATURE_NEON_FMA
Indicates that the device's CPU supports fused multiply-accumulate
NEON instructions extension. Also part of the VFPv4 specification.
ANDROID_CPU_ARM_FEATURE_IDIV_ARM
Indicates that the device's CPU supports Integer division in ARM mode.
Only available on recent CPUs (e.g. Cortex-A15).
ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2
Indicates that the device's CPU supports Integer division in Thumb-2
mode. Only available on recent CPUs (e.g. Cortex-A15).
ANDROID_CPU_ARM_FEATURE_iWMMXt
Indicates that the device's CPU supports extension that adds MMX
registers and instructions. This is only available on a few XScale-
based CPU.
ANDROID_CPU_ARM_FEATURE_LDREX_STREX
Indicates that the device's CPU supports LDREX and STREX instructions
available since ARMv6. Together they provide atomic update on memory
with the help of exclusive monitor.
And the following flags for the x86 CPU Family:
ANDROID_CPU_X86_FEATURE_SSSE3
Indicates that the device's CPU supports the SSSE3 instruction
extension set. Note that this is unlike SSE3 which is required
by the x86 NDK ABI.
ANDROID_CPU_X86_FEATURE_POPCNT
Indicates that the device's CPU supports the POPCNT instruction.
ANDROID_CPU_X86_FEATURE_MOVBE
Indicates that the device's CPU supports the MOVBE instruction.
This one is specific to some Intel IA-32 CPUs, like the Atom.
The following function is also defined to return the max number of
CPU cores on the target device:
int android_getCpuCount(void);
Important Note:
---------------
The cpufeatures library will be updated to support more CPU families and
optional features in the future. It is designed to work as-is on all
official Android platform versions.
Change History:
---------------
Please see the comments in $NDK/sources/android/cpufeatures/cpu-features.c
for the complete change history for this library.
//
cpu-features.h
/*
* 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
typedef enum {
ANDROID_CPU_FAMILY_UNKNOWN = 0,
ANDROID_CPU_FAMILY_ARM,
ANDROID_CPU_FAMILY_X86,
ANDROID_CPU_FAMILY_MIPS,
ANDROID_CPU_FAMILY_MAX /* do not remove */
} AndroidCpuFamily;
/* Return family of the device's CPU */
extern AndroidCpuFamily android_getCpuFamily(void);
/* The list of feature flags for ARM CPUs that can be recognized by the
* library. 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.
*
* 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.
*/
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),
};
enum {
ANDROID_CPU_X86_FEATURE_SSSE3 = (1 << 0),
ANDROID_CPU_X86_FEATURE_POPCNT = (1 << 1),
ANDROID_CPU_X86_FEATURE_MOVBE = (1 << 2),
};
extern uint64_t android_getCpuFeatures(void);
/* 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);
__END_DECLS
#endif /* CPU_FEATURES_H */
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