Use getauxval() if available.

This fixes the problem of not being able to detect ARM features on
ChromeOS because sandbox cannot access /proc/self/auxv and
/proc/cpuinfo there.

Drive-by-cleanup to libc detection in two other places.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/672543002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24789 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8config.h

@@ -120,7 +120,6 @@
 //  V8_LIBC_BIONIC  - Bionic libc
 //  V8_LIBC_BSD     - BSD libc derivate
 //  V8_LIBC_GLIBC   - GNU C library
-//  V8_LIBC_UCLIBC  - uClibc
 //
 // Note that testing for libc must be done using #if not #ifdef. For example,
 // to test for the GNU C library, use:
@@ -133,8 +132,6 @@
 #elif defined(__BIONIC__)
 # define V8_LIBC_BIONIC 1
 # define V8_LIBC_BSD 1
-#elif defined(__UCLIBC__)
-# define V8_LIBC_UCLIBC 1
 #elif defined(__GLIBC__) || defined(__GNU_LIBRARY__)
 # define V8_LIBC_GLIBC 1
 #else

src/base/cpu.cc

@@ -7,12 +7,18 @@
 #if V8_LIBC_MSVCRT
 #include <intrin.h>  // __cpuid()
 #endif
-#if V8_OS_POSIX
-#include <unistd.h>  // sysconf()
+#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
 
 #include <ctype.h>
 #include <limits.h>
@@ -92,11 +98,12 @@ static V8_INLINE void __cpuid(int cpu_info[4], int info_type) {
 #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;
@@ -112,6 +119,7 @@ static uint32_t ReadELFHWCaps() {
     }
     fclose(fp);
   }
+#endif
   return result;
 }
 
@@ -310,7 +318,7 @@ CPU::CPU() : stepping_(0),
              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.

src/sampler.cc

@@ -374,8 +374,7 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
   state.sp = reinterpret_cast<Address>(mcontext.gregs[REG_RSP]);
   state.fp = reinterpret_cast<Address>(mcontext.gregs[REG_RBP]);
 #elif V8_HOST_ARCH_ARM
-#if defined(__GLIBC__) && !defined(__UCLIBC__) && \
-    (__GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ <= 3))
+#if V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
   // Old GLibc ARM versions used a gregs[] array to access the register
   // values from mcontext_t.
   state.pc = reinterpret_cast<Address>(mcontext.gregs[R15]);
@@ -385,8 +384,7 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
   state.pc = reinterpret_cast<Address>(mcontext.arm_pc);
   state.sp = reinterpret_cast<Address>(mcontext.arm_sp);
   state.fp = reinterpret_cast<Address>(mcontext.arm_fp);
-#endif  // defined(__GLIBC__) && !defined(__UCLIBC__) &&
-        // (__GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ <= 3))
+#endif  // V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
 #elif V8_HOST_ARCH_ARM64
   state.pc = reinterpret_cast<Address>(mcontext.pc);
   state.sp = reinterpret_cast<Address>(mcontext.sp);