Use getauxval() if available.

src/base/cpu.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/cpu.h"
 
 #if V8_LIBC_MSVCRT
 #include <intrin.h>  // __cpuid()
 #endif
+#if V8_OS_LINUX
+#include <linux/auxvec.h>  // AT_HWCAP
+#endif
+#if V8_GLIBC_PREREQ(2, 16)
+#include <sys/auxv.h>  // getauxval()
+#endif
+#if V8_OS_QNX
+#include <sys/syspage.h>  // cpuinfo
+#endif
 #if V8_OS_POSIX
 #include <unistd.h>  // sysconf()
 #endif
-#if V8_OS_QNX
-#include <sys/syspage.h>  // cpuinfo
-#endif
 
 #include <ctype.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <algorithm>
 
 #include "src/base/logging.h"
 #if V8_OS_WIN
@@ skipping 59 matching lines @@
 #define HWCAP_VFPv3 (1 << 13)
 #define HWCAP_VFPv3D16  (1 << 14) /* also set for VFPv4-D16 */
 #define HWCAP_TLS (1 << 15)
 #define HWCAP_VFPv4 (1 << 16)
 #define HWCAP_IDIVA (1 << 17)
 #define HWCAP_IDIVT (1 << 18)
 #define HWCAP_VFPD32  (1 << 19) /* set if VFP has 32 regs (not 16) */
 #define HWCAP_IDIV  (HWCAP_IDIVA | HWCAP_IDIVT)
 #define HWCAP_LPAE  (1 << 20)
 
-#define AT_HWCAP 16
-
-// Read the ELF HWCAP flags by parsing /proc/self/auxv.
 static uint32_t ReadELFHWCaps() {
   uint32_t result = 0;
+#if V8_GLIBC_PREREQ(2, 16)
+  result = static_cast<uint32_t>(getauxval(AT_HWCAP));
+#else
+  // Read the ELF HWCAP flags by parsing /proc/self/auxv.
   FILE* fp = fopen("/proc/self/auxv", "r");
   if (fp != NULL) {
     struct { uint32_t tag; uint32_t value; } entry;
     for (;;) {
       size_t n = fread(&entry, sizeof(entry), 1, fp);
       if (n == 0 || (entry.tag == 0 && entry.value == 0)) {
         break;
       }
       if (entry.tag == AT_HWCAP) {
         result = entry.value;
         break;
       }
     }
     fclose(fp);
   }
+#endif
   return result;
 }
 
 #endif  // V8_HOST_ARCH_ARM
 
 #if V8_HOST_ARCH_MIPS
 int __detect_fp64_mode(void) {
   double result = 0;
   // Bit representation of (double)1 is 0x3FF0000000000000.
   __asm__ volatile(
@@ skipping 178 matching lines @@
              has_sse41_(false),
              has_sse42_(false),
              has_idiva_(false),
              has_neon_(false),
              has_thumb2_(false),
              has_vfp_(false),
              has_vfp3_(false),
              has_vfp3_d32_(false),
              is_fp64_mode_(false) {
   memcpy(vendor_, "Unknown", 8);
-#if defined(__pnacl__)
+#if V8_OS_NACL
 // Portable host shouldn't do feature detection.
 // TODO(jfb): Remove the hardcoded ARM simulator flags in the build, and
 // hardcode them here instead.
 #elif V8_HOST_ARCH_IA32 || V8_HOST_ARCH_X64
   int cpu_info[4];
 
   // __cpuid with an InfoType argument of 0 returns the number of
   // valid Ids in CPUInfo[0] and the CPU identification string in
   // the other three array elements. The CPU identification string is
   // not in linear order. The code below arranges the information
@@ skipping 219 matching lines @@
     if (end == part) {
       part_ = 0;
     }
     delete[] part;
   }
 
 #endif
 }
 
 } }  // namespace v8::base