ARM处理器Linux下浮点运算单元运用

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./ Toradex Colibri/Apalis i.MX6/T30编译器选项

取决于在mfloat-abi选项所配置的调用约定为"softfp" 还是"hard"

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-march=armv7-a -mfloat-abi=xxx -mfpu=neon -mtune=cortex-a9 -O3

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./ Toradex Colibri VFxx编译器选项

取决于在mfloat-abi选项所配置的调用约定为"softfp" 还是"hard"，未来可以通过更多的mfpu 选项来优化NEON的实现。

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-march=armv7-a -mfloat-abi=xxx -mfpu=neon -mtune=cortex-a5 -O3

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5). 检测一个二进制文件的浮点调用约定

同样以Toradex产品为例，其所发布的Linux Images 所有的object 目标文件都使用ELF，详细介绍请参考：

en.wikipedia.org/wiki/Executable_and_Linkable_Format

首先架构信息（如i686 或者ARM）可以通过" file afile "程序来获取，架构相关属性信息可以通过" readelf –A afile "程序来获取 （原生或者交叉编译ToolChain都可以使用readelf）

如果readelf命令输出信息里面包含"Tag_ABI_VFP_args: VFP registers"，则调用约定为硬浮点；如没有，则为软浮点。

./ 以Colibri T20 编译的共享目标文件为例

•使用 VFPv3-D16 指令和寄存器

•不使用 SIMD extensions

•硬调用约定

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$ file colibri-t20/usr/lib/libcurl.so.5.3.0

colibri-t20/usr/lib/libcurl.so.5.3.0: ELF 32-bit LSB shared object, ARM, version 1 (SYSV), dynamically linked, not stripped

$ readelf -A colibri-t20/usr/lib/libcurl.so.5.3.0

Attribute Section: aeabi

File Attributes

Tag_CPU_name: "7-A"

Tag_CPU_arch: v7

Tag_CPU_arch_profile: Application

Tag_ARM_ISA_use: Yes

Tag_THUMB_ISA_use: Thumb-2

Tag_FP_arch: VFPv3-D16

Tag_ABI_PCS_wchar_t: 4

Tag_ABI_FP_denormal: Needed

Tag_ABI_FP_exceptions: Needed

Tag_ABI_FP_number_model: IEEE 754

Tag_ABI_align_needed: 8-byte

Tag_ABI_align_preserved: 8-byte, except leaf SP

Tag_ABI_enum_size: int

Tag_ABI_HardFP_use: SP and DP

Tag_ABI_VFP_args: VFP registers

Tag_CPU_unaligned_access: v6

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./ 以NXP/Freescale Vybrid 编译的共享目标文件为例

•使用 VFPv3 指令和寄存器

•使用用 NEON SIMD extensions

•软调用约定

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$ file twr-vf65gs10/usr/lib/libcurl.so.5.3.0

twr-vf65gs10/usr/lib/libcurl.so.5.3.0: ELF 32-bit LSB shared object, ARM, version 1 (SYSV), dynamically linked, not stripped

$ readelf -A twr-vf65gs10/usr/lib/libcurl.so.5.3.0

Attribute Section: aeabi

File Attributes

Tag_CPU_name: "7-A"

Tag_CPU_arch: v7

Tag_CPU_arch_profile: Application

Tag_ARM_ISA_use: Yes

Tag_THUMB_ISA_use: Thumb-2

Tag_FP_arch: VFPv3

Tag_Advanced_SIMD_arch: NEONv1

Tag_ABI_PCS_wchar_t: 4

Tag_ABI_FP_denormal: Needed

Tag_ABI_FP_exceptions: Needed

Tag_ABI_FP_number_model: IEEE 754

Tag_ABI_align_needed: 8-byte

Tag_ABI_align_preserved: 8-byte, except leaf SP

Tag_ABI_enum_size: int

Tag_ABI_HardFP_use: SP and DP

Tag_CPU_unaligned_access: v6

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./ 以Colibri PXA 编译的共享目标文件为例

•不使用浮点运算单元

•不使用SIMD extensions

•软调用约定

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