[NOT TO COMMIT!] Merge Chromium-specific changes in tcmalloc thru. the original gperftools r136.

third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h

 /* Copyright (c) 2009, Google Inc.
  * 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
@@ skipping 23 matching lines @@
 #include <errno.h>
 #include <sched.h>
 #include <time.h>
 #include <limits.h>
 #include "base/linux_syscall_support.h"
 
 #define FUTEX_WAIT 0
 #define FUTEX_WAKE 1
 #define FUTEX_PRIVATE_FLAG 128
 
+// Note: Instead of making direct system calls that are inlined, we rely
+//       on the syscall() function in glibc to do the right thing. This
+//       is necessary to make the code compatible with the seccomp sandbox,
+//       which needs to be able to find and patch all places where system
+//       calls are made. Scanning through and patching glibc is fast, but
+//       doing so on the entire Chrome binary would be prohibitively
+//       expensive.
+//       This is a notable change from the upstream version of tcmalloc,
+//       which prefers direct system calls in order to improve compatibility
+//       with older toolchains and runtime libraries.
+
 static bool have_futex;
 static int futex_private_flag = FUTEX_PRIVATE_FLAG;
 
 namespace {
 static struct InitModule {
   InitModule() {
     int x = 0;
     // futexes are ints, so we can use them only when
     // that's the same size as the lockword_ in SpinLock.
 #ifdef __arm__
     // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
     have_futex = 0;
 #else
-    have_futex = (sizeof (Atomic32) == sizeof (int) &&
-                  sys_futex(&x, FUTEX_WAKE, 1, 0) >= 0);
+    have_futex = (sizeof (Atomic32) == sizeof (int) && 
+                  syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
 #endif
     if (have_futex &&
-        sys_futex(&x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
+        syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
       futex_private_flag = 0;
     }
   }
 } init_module;
 
 }  // anonymous namespace
 
 
 namespace base {
 namespace internal {
 
 void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
   if (loop != 0) {
     int save_errno = errno;
     struct timespec tm;
     tm.tv_sec = 0;
     if (have_futex) {
       tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
     } else {
       tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
     }
     if (have_futex) {
       tm.tv_nsec *= 16;  // increase the delay; we expect explicit wakeups
-      sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
+      syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
                 FUTEX_WAIT | futex_private_flag,
                 value, reinterpret_cast<struct kernel_timespec *>(&tm));
     } else {
       nanosleep(&tm, NULL);
     }
     errno = save_errno;
   }
 }
 
 void SpinLockWake(volatile Atomic32 *w, bool all) {
   if (have_futex) {
-    sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
-              FUTEX_WAKE | futex_private_flag, all? INT_MAX : 1, 0);
+    syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
+              FUTEX_WAKE | futex_private_flag, 1, 0);
   }
 }
 
 } // namespace internal
 } // namespace base