Reland "MIPS: Add support for arch. revision 6 to mips32 port."

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_POSIX
@@ skipping 97 matching lines @@
         break;
       }
     }
     fclose(fp);
   }
   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(
+    "lui $t0, 0x3FF0\n\t"
+    "ldc1 $f0, %0\n\t"
+    "mtc1 $t0, $f1\n\t"
+    "sdc1 $f0, %0\n\t"
+    : "+m" (result)
+    : : "t0", "$f0", "$f1", "memory");
+
+  return !(result == 1);
+}
+
+
+int __detect_mips_arch_revision(void) {
+  // TODO(dusmil): Do the specific syscall as soon as it is implemented in mips
+  // kernel. Currently fail-back to the least common denominator which is
+  // mips32 revision 1.
+  return 1;
+}
+#endif
+
 // Extract the information exposed by the kernel via /proc/cpuinfo.
 class CPUInfo V8_FINAL {
  public:
   CPUInfo() : datalen_(0) {
     // Get the size of the cpuinfo file by reading it until the end. This is
     // required because files under /proc do not always return a valid size
     // when using fseek(0, SEEK_END) + ftell(). Nor can the be mmap()-ed.
     static const char PATHNAME[] = "/proc/cpuinfo";
     FILE* fp = fopen(PATHNAME, "r");
     if (fp != NULL) {
@@ skipping 331 matching lines @@
 
   // Simple detection of FPU at runtime for Linux.
   // It is based on /proc/cpuinfo, which reveals hardware configuration
   // to user-space applications.  According to MIPS (early 2010), no similar
   // facility is universally available on the MIPS architectures,
   // so it's up to individual OSes to provide such.
   CPUInfo cpu_info;
   char* cpu_model = cpu_info.ExtractField("cpu model");
   has_fpu_ = HasListItem(cpu_model, "FPU");
   delete[] cpu_model;
+#ifdef V8_HOST_ARCH_MIPS
+  is_fp64_mode_ = __detect_fp64_mode();
+  architecture_ = __detect_mips_arch_revision();
+#endif
 
 #elif V8_HOST_ARCH_ARM64
 
   CPUInfo cpu_info;
 
   // Extract implementor from the "CPU implementer" field.
   char* implementer = cpu_info.ExtractField("CPU implementer");
   if (implementer != NULL) {
     char* end ;
     implementer_ = strtol(implementer, &end, 0);
@@ skipping 11 matching lines @@
     if (end == part) {
       part_ = 0;
     }
     delete[] part;
   }
 
 #endif
 }
 
 } }  // namespace v8::base