Support profiling based on linux kernel performance events.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index f7d8609b978bc01076e4e8d14d177addc66fe0bc..b42c3ef91333a530ca24df4fcbfd7801bdb10c22 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -397,6 +397,30 @@ void OS::LogSharedLibraryAddresses() {
 }
 
 
+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__