本文共 1754 字，大约阅读时间需要 5 分钟。

在ceph 的src/test/test_arch.cc 中我们可以看到下面的code ，从kernel中的/proc/cpuinfo 中的feature来判断arm是否支持neon指令，需要注意这个指令在armv8 之后被称为asimd指令TEST(Arch, all){  ceph_arch_probe();  EXPECT_TRUE(ceph_arch_probed);#if (__arm__ || __aarch64__ || __x86_64__) && __linux__  char flags[FLAGS_SIZE];  FILE *f = popen("grep '^\\(flags\\|Features\\)[        ]*:' "                  "/proc/cpuinfo | head -1", "r");  if(f == NULL || fgets(flags, FLAGS_SIZE - 1, f) == NULL) {    // silently do nothing if /proc/cpuinfo does exist, is not    // readable or does not contain the expected information    if (f)      pclose(f);    return;  }  pclose(f);  flags[strlen(flags) - 1] = ' ';  int expected;#if (__arm__ || __aarch64__)#从这里知道neon和asimd 是一回事  expected = (strstr(flags, " neon ") || strstr(flags, " asimd ")) ? 1 : 0;  EXPECT_EQ(expected, ceph_arch_neon);#endif除了通过/proc/cpuinfo 外更通用的方式是通过/proc/self/auxv 来获取硬件featurestatic unsigned long get_auxval(unsigned long type){	unsigned long result = 0;	#打开这个文件	FILE *f = fopen("/proc/self/auxv", "r");	if (f) {		ElfW(auxv_t) entry;		#读取这个文件的AT_HWCAP		while (fread(&entry, sizeof(entry), 1, f) == 1) {			if (entry.a_type == type) {				result = entry.a_un.a_val;				break;			}		}		fclose(f);	}	return result;}static unsigned long get_hwcap(void){	return get_auxval(AT_HWCAP);}#endif // __linux__int ceph_arch_arm_probe(void){#从下面这段code 也可以知道arm下的neon 指令等同于arm64下的asimd指令#if __arm__ && __linux__	ceph_arch_neon = (get_hwcap() & HWCAP_NEON) == HWCAP_NEON;#elif __aarch64__ && __linux__	ceph_arch_neon = (get_hwcap() & HWCAP_ASIMD) == HWCAP_ASIMD;# if defined(HAVE_ARMV8_CRC) && defined(HWCAP_CRC32)	ceph_arch_aarch64_crc32 = (get_hwcap() & HWCAP_CRC32) == HWCAP_CRC32;# endif#else	if (0)		get_hwcap();  // make compiler shut up#endif	return 0;}

转载地址：http://xjnmi.baihongyu.com/