Revert "Revisiting auxvec data gathering for PPC/ARM."

This reverts commit f5bee002.

Reason for revert: Crashes android webview, see https://crbug.com/1071708.

Original change's description:
> Revisiting auxvec data gathering for PPC/ARM.
> 
> /proc/sys/auxv might not be accessible, instead
> getting these from the user's stack.
> 
> Change-Id: I2dcf696734e2b4dc1da27a991930b9e0d4228d51
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1730990
> Commit-Queue: Clemens Backes [né Hammacher] <clemensb@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Clemens Backes [né Hammacher] <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64037}

TBR=clemensb@chromium.org,bmeurer@chromium.org,devnexen@gmail.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:1071708
Change-Id: I05659f245c1020e98b7225a25e82987d9955d595
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154800Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67234}

src/base/cpu.cc

@@ -9,7 +9,6 @@
 #endif
 #if V8_OS_LINUX
 #include <linux/auxvec.h>  // AT_HWCAP
-extern "C" char** environ;
 #endif
 #if V8_GLIBC_PREREQ(2, 16)
 #include <sys/auxv.h>  // getauxval()
@@ -17,7 +16,7 @@ extern "C" char** environ;
 #if V8_OS_QNX
 #include <sys/syspage.h>  // cpuinfo
 #endif
-#if (V8_OS_LINUX && (V8_HOST_ARCH_PPC || V8_HOST_ARCH_PPC64)) || V8_OS_ANDROID
+#if V8_OS_LINUX && (V8_HOST_ARCH_PPC || V8_HOST_ARCH_PPC64)
 #include <elf.h>
 #endif
 #if V8_OS_AIX
@@ -110,25 +109,31 @@ static V8_INLINE void __cpuid(int cpu_info[4], int info_type) {
 #define HWCAP_LPAE  (1 << 20)
 
 static uint32_t ReadELFHWCaps() {
+  uint32_t result = 0;
 #if V8_GLIBC_PREREQ(2, 16)
-  return static_cast<uint32_t>(getauxval(AT_HWCAP));
-#else
-  char** head = environ;
-  while (*head++ != nullptr) {
-  }
-#ifdef __LP64__
-  using elf_auxv_t = Elf64_auxv_t;
+  result = static_cast<uint32_t>(getauxval(AT_HWCAP));
 #else
-  using elf_auxv_t = Elf32_auxv_t;
-#endif
-  for (elf_auxv_t* entry = reinterpret_cast<elf_auxv_t*>(head);
-       entry->a_type != AT_NULL; ++entry) {
-    if (entry->a_type == AT_HWCAP) {
-      return entry->a_un.a_val;
+  // Read the ELF HWCAP flags by parsing /proc/self/auxv.
+  FILE* fp = fopen("/proc/self/auxv", "r");
+  if (fp != nullptr) {
+    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);
   }
-  return 0u;
 #endif
+  return result;
 }
 
 #endif  // V8_HOST_ARCH_ARM
@@ -610,28 +615,33 @@ CPU::CPU()
 
 #ifndef USE_SIMULATOR
 #if V8_OS_LINUX
+  // Read processor info from /proc/self/auxv.
   char* auxv_cpu_type = nullptr;
-  char** head = environ;
-  while (*head++ != nullptr) {
-  }
+  FILE* fp = fopen("/proc/self/auxv", "r");
+  if (fp != nullptr) {
 #if V8_TARGET_ARCH_PPC64
-  using elf_auxv_t = Elf64_auxv_t;
+    Elf64_auxv_t entry;
 #else
-  using elf_auxv_t = Elf32_auxv_t;
+    Elf32_auxv_t entry;
 #endif
-  for (elf_auxv_t* entry = reinterpret_cast<elf_auxv_t*>(head);
-       entry->a_type != AT_NULL; ++entry) {
-    switch (entry->a_type) {
-      case AT_PLATFORM:
-        auxv_cpu_type = reinterpret_cast<char*>(entry->a_un.a_val);
-        break;
-      case AT_ICACHEBSIZE:
-        icache_line_size_ = entry->a_un.a_val;
-        break;
-      case AT_DCACHEBSIZE:
-        dcache_line_size_ = entry->a_un.a_val;
+    for (;;) {
+      size_t n = fread(&entry, sizeof(entry), 1, fp);
+      if (n == 0 || entry.a_type == AT_NULL) {
         break;
+      }
+      switch (entry.a_type) {
+        case AT_PLATFORM:
+          auxv_cpu_type = reinterpret_cast<char*>(entry.a_un.a_val);
+          break;
+        case AT_ICACHEBSIZE:
+          icache_line_size_ = entry.a_un.a_val;
+          break;
+        case AT_DCACHEBSIZE:
+          dcache_line_size_ = entry.a_un.a_val;
+          break;
+      }
     }
+    fclose(fp);
   }
 
   part_ = -1;