为什么编译器没有定义 __ARM_FEATURE_CRC32?

发布时间：2023/10/11 编译器

本文介绍了为什么编译器没有定义 __ARM_FEATURE_CRC32?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我已经研究这个问题一段时间了，我希望有人能指出我的错误.我想我再也看不到森林了.

I've been working on this issue for some time now, and I hope someone can point out my mistake. I guess I can no longer see the forest through the trees.

我有一个用于测试的 LeMaker HiKey 开发板.它的 AArch64，因此它具有 NEON 和其他 cpu 功能，如 AES、SHA 和 CRC32:

I have a LeMaker HiKey dev board I use for testing. Its AArch64, so its has NEON and the other cpu features like AES, SHA and CRC32:

$ cat /proc/cpuinfo 
Processor   : AArch64 Processor rev 3 (aarch64)
...
Features    : fp asimd evtstrm aes pmull sha1 sha2 crc32 
...

当我尝试编译程序时:

$ cat test.cxx
#if (defined(__ARM_NEON__) || defined(__ARM_NEON))
# define NEON_INTRINSICS_AVAILABLE 1
#else
# define NEON_INTRINSICS_AVAILABLE 0
#endif

#if BOOL_NEON_INTRINSICS_AVAILABLE
# include <arm_neon.h>
# if defined(__ARM_FEATURE_CRC32) || (__ARM_ACLE >= 200)
#  include <arm_acle.h>
# endif
#endif

#include <stdint.h>

int main(int argc, char* argv[])
{
  uint32_t crc = 0;

  crc = __crc32b(crc, (uint8_t)0);
  return 0
}

结果如下:

$ g++ test.cxx -o test.exe
test.cxx: In function ‘int main(int, char**)’:
test.cxx:20:33: error: ‘__crc32b’ was not declared in this scope
   crc = __crc32b(crc, (uint8_t)0);
                                 ^
test.cxx:22:1: error: expected ‘;’ before ‘}’ token
 }
 ^

$ clang++ test.cxx -o test.exe
test.cxx:20:9: error: use of undeclared identifier '__crc32b'
  crc = __crc32b(crc, (uint8_t)0);
        ^
test.cxx:21:11: error: expected ';' after return statement
  return 0
          ^
          ;
2 errors generated.

文件系统的 grep 显示 arm_acle.h 实际上是标题:

A grep of the file system reveals arm_acle.h is in fact the header:

$ grep -IR '__crc32' /usr/lib
/usr/lib/gcc/.../include/arm_acle.h:__crc32b (uint32_t __a, uint8_t __b)
...

根据 ARM® C Language Extensions，第 9.7 节 CRC32 Intrinsics，假设在定义 __ARM_FEATURE_CRC32 时会出现缺失的符号.检查 arm_acle.h 即可确认.

And according to ARM® C Language Extensions, Section 9.7 CRC32 Intrinsics, the missing symbols are suppose be present when __ARM_FEATURE_CRC32 is defined. Inspecting arm_acle.h confirms it.

为了完整起见，我尝试使用 -march=native 进行编译，但编译器拒绝了它.

For completeness, I tried compiling with -march=native, but the compiler rejected it.