Support profiling based on linux kernel performance events.

src/platform-linux.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 379 matching lines @@
       } while ((c != EOF) && (c != '\n'));
       if (c == EOF) break;
     }
   }
   free(lib_name);
   fclose(fp);
 #endif
 }
 
 
+static const char kGCFakeMmap[] = "/tmp/__v8_gc__";
+
+
+void OS::SignalCodeMovingGC() {
+#ifdef ENABLE_LOGGING_AND_PROFILING
+  // Support for ll_prof.py.
+  //
+  // The Linux profiler built into the kernel logs all mmap's with
+  // PROT_EXEC so that analysis tools can properly attribute ticks. We
+  // do a mmap with a name known by ll_prof.py and immediately munmap
+  // it. This injects a GC marker into the stream of events generated
+  // by the kernel and allows us to synchronize V8 code log and the
+  // kernel log.
+  int size = sysconf(_SC_PAGESIZE);
+  FILE* f = fopen(kGCFakeMmap, "w+");
+  void* addr = mmap(NULL, size, PROT_READ | PROT_EXEC, MAP_PRIVATE,
+                    fileno(f), 0);
+  ASSERT(addr != MAP_FAILED);
+  munmap(addr, size);
+  fclose(f);
+#endif
+}
+
+
 int OS::StackWalk(Vector<OS::StackFrame> frames) {
   // backtrace is a glibc extension.
 #ifdef __GLIBC__
   int frames_size = frames.length();
   ScopedVector<void*> addresses(frames_size);
 
   int frames_count = backtrace(addresses.start(), frames_size);
 
   char** symbols = backtrace_symbols(addresses.start(), frames_count);
   if (symbols == NULL) {
@@ skipping 445 matching lines @@
 
   // This sampler is no longer the active sampler.
   active_sampler_ = NULL;
   active_ = false;
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal