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在上一篇博文《海光处理器与AMD Zen1的指令差异-CSDN博客》中发现，海光相比AMD，缺失了一些指令集。
那么在AMD或Intel上编译出来的程序，可以跑在海光上吗？
这个问题的关键，在于编译器默认使用哪些指令来编译程序。以CentOS8.4为例，它自带的gcc版本为gcc version 8.4.1 20200928：
| [root@CentOS8 ~]# gcc -v Using built-in specs. COLLECT_GCC=/usr/bin/gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/8/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-redhat-linux Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --disable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=x86-64 --build=x86_64-redhat-linux Thread model: posix gcc version 8.4.1 20200928 (Red Hat 8.4.1-1) (GCC) |
gcc在编译的时候，可通过-march=来指定要使用的指令范围，默认值为-march=x86-64，这个默认值是构建gcc自身时指定的，即上表中的--with-arch_32=x86-64。
接下来看一下-march=x86-64代表的指令范围。
| [root@CentOS8 ~]# gcc -march=x86-64 -c -Q --help=target | grep -i enabled -m128bit-long-double [enabled] -m64 [enabled] -m80387 [enabled] -malign-stringops [enabled] -mavx256-split-unaligned-load [enabled] -mavx256-split-unaligned-store [enabled] -mfancy-math-387 [enabled] -mfp-ret-in-387 [enabled] -mfxsr [enabled] -mglibc [enabled] -mhard-float [enabled] -mieee-fp [enabled] -mlong-double-80 [enabled] -mmmx [enabled] -mno-sse4 [enabled] -mpush-args [enabled] -mred-zone [enabled] -msse [enabled] -msse2 [enabled] -mstv [enabled] -mtls-direct-seg-refs [enabled] -mvzeroupper [enabled] |
这些指令代表什么意思呢？
| -march=x86-64 of GCC8.4.1(CentOS8.4) | x86-64 | Instructions |
| m128bit-long-double | [enabled] | sizeof(long double) is 16. |
| m64 | [enabled] | Generate 64bit x86-64 code. |
| m80387 | [enabled] | Use hardware fp. |
| malign-stringops | [enabled] | Align destination of the string operations. |
| march= | x86-64 | Generate code for given CPU. |
| mavx256-split-unaligned-load | [enabled] | d Split 32-byte AVX unaligned load. |
| mavx256-split-unaligned-store | [enabled] | re Split 32-byte AVX unaligned store. |
| mfancy-math-387 | [enabled] | Generate sin, cos, sqrt for FPU. |
| mfp-ret-in-387 | [enabled] | Return values of functions in FPU registers. |
| mfxsr | [enabled] | Support FXSAVE and FXRSTOR instructions. |
| mglibc | [enabled] | Use GNU C library. |
| mhard-float | [enabled] | Use hardware fp. |
| mieee-fp | [enabled] | Use IEEE math for fp comparisons. |
| mlong-double-80 | [enabled] | Use 80-bit long double. |
| mmmx | [enabled] | Support MMX built-in functions. |
| mno-sse4 | [enabled] | Do not support SSE4.1 and SSE4.2 built-in functions and code generation. |
| mpush-args | [enabled] | Use push instructions to save outgoing arguments. |
| mred-zone | [enabled] | Use red-zone in the x86-64 code. |
| msse | [enabled] | Support MMX and SSE built-in functions and code generation. |
| msse2 | [enabled] | Support MMX, SSE and SSE2 built-in functions and code generation. |
| mstv | [enabled] | Disable Scalar to Vector optimization pass transforming 64-bit integer computations into a vector ones. |
| mtls-direct-seg-refs | [enabled] | Use direct references against %gs when accessing tls data. |
| mvzeroupper | [enabled] | Generate vzeroupper instruction before a transfer of control flow out of the function. |
很明显，这个-march=x86-64代表的指令范围很小，海光全部都支持。所以，默认情况下，在AMD上编译的程序，依然可以跑在海光上。
如果gcc编译的时候指定-march=znver1，那么海光可以运行吗？答案是否定的，因为至少有2个指令集海光是不支持的：aes和pclmul。
只有一种特例：那就是程序本身并不涉及加解密，编译之后的汇编代码不包括aes和pclmul相关指令，即使编译的时候指定-march=znver1，那么这个程序还是可以跑在海光上的。
| -march=??? of GCC8.4.1(CentOS8.4) | x86-64 | znver1 |
| m128bit-long-double | [enabled] | [enabled] |
| m64 | [enabled] | [enabled] |
| m80387 | [enabled] | [enabled] |
| mabm | [disabled] | [enabled] |
| madx | [disabled] | [enabled] |
| maes | [disabled] | [enabled] |
| malign-stringops | [enabled] | [enabled] |
| march= | x86-64 | znver1 |
| mavx | [disabled] | [enabled] |
| mavx2 | [disabled] | [enabled] |
| mavx256-split-unaligned-store | [enabled] | [enabled] |
| mbmi | [disabled] | [enabled] |
| mbmi2 | [disabled] | [enabled] |
| mclflushopt | [disabled] | [enabled] |
| mclzero | [disabled] | [enabled] |
| mcx16 | [disabled] | [enabled] |
| mf16c | [disabled] | [enabled] |
| mfancy-math-387 | [enabled] | [enabled] |
| mfma | [disabled] | [enabled] |
| mfp-ret-in-387 | [enabled] | [enabled] |
| mfsgsbase | [disabled] | [enabled] |
| mfxsr | [enabled] | [enabled] |
| mglibc | [enabled] | [enabled] |
| mhard-float | [enabled] | [enabled] |
| mieee-fp | [enabled] | [enabled] |
| mlong-double-80 | [enabled] | [enabled] |
| mlzcnt | [disabled] | [enabled] |
| mmmx | [enabled] | [enabled] |
| mmovbe | [disabled] | [enabled] |
| mmwaitx | [disabled] | [enabled] |
| mpclmul | [disabled] | [enabled] |
| mpopcnt | [disabled] | [enabled] |
| mprfchw | [disabled] | [enabled] |
| mpush-args | [enabled] | [enabled] |
| mrdrnd | [disabled] | [enabled] |
| mrdseed | [disabled] | [enabled] |
| mred-zone | [enabled] | [enabled] |
| msahf | [disabled] | [enabled] |
| msha | [disabled] | [enabled] |
| msse | [enabled] | [enabled] |
| msse2 | [enabled] | [enabled] |
| msse3 | [disabled] | [enabled] |
| msse4 | [disabled] | [enabled] |
| msse4.1 | [disabled] | [enabled] |
| msse4.2 | [disabled] | [enabled] |
| msse4a | [disabled] | [enabled] |
| mssse3 | [disabled] | [enabled] |
| mstv | [enabled] | [enabled] |
| mtls-direct-seg-refs | [enabled] | [enabled] |
| mtune= | generic | znver1 |
| mvzeroupper | [enabled] | [enabled] |
| mxsave | [disabled] | [enabled] |
| mxsavec | [disabled] | [enabled] |
| mxsaveopt | [disabled] | [enabled] |
| mxsaves | [disabled] | [enabled] |
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