linux, android: Always assume futex syscall is availabble.

Bug: 897742
Change-Id: Id980269ea623f9800b62aead3896d107690a64eb
Reviewed-on: https://chromium-review.googlesource.com/c/1293559Reviewed-by: Primiano Tucci <primiano@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601583}

third_party/tcmalloc/README.chromium

@@ -115,3 +115,4 @@ Modifications:
 - Pulled SuggestedDelayNS() implementation for 32bit architectures which do not support 64bit atomicity
 - Pulled several mipsel related changes from lss project to fix compile errors
 - Fixed line endings in vendor/README_windows.txt to Unix (LF)
+- Removed have_futex from spinlock_linux-inl.h; assume it's always there

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

@@ -53,27 +53,6 @@
 //       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.
-    have_futex = (sizeof(Atomic32) == sizeof(int) &&
-                  syscall(__NR_futex, &x, FUTEX_WAKE, 1, NULL, NULL, 0) >= 0);
-    if (have_futex && syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag,
-                              1, NULL, NULL, 0) < 0) {
-      futex_private_flag = 0;
-    }
-  }
-} init_module;
-
-}  // anonymous namespace
-
-
 namespace base {
 namespace internal {
 
@@ -82,28 +61,18 @@ void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
     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
-      syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
-              FUTEX_WAIT | futex_private_flag, value,
-              reinterpret_cast<struct kernel_timespec*>(&tm), NULL, 0);
-    } else {
-      nanosleep(&tm, NULL);
-    }
+    tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
+    tm.tv_nsec *= 16;  // increase the delay; we expect explicit wakeups
+    syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
+            FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value,
+            reinterpret_cast<struct kernel_timespec*>(&tm), NULL, 0);
     errno = save_errno;
   }
 }
 
 void SpinLockWake(volatile Atomic32 *w, bool all) {
-  if (have_futex) {
-    syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
-            FUTEX_WAKE | futex_private_flag, all ? INT_MAX : 1, NULL, NULL, 0);
-  }
+  syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
+          FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, NULL, NULL, 0);
 }
 
 } // namespace internal

third_party/tcmalloc/gperftools-2.0/chromium/src/base/spinlock_linux-inl.h

@@ -41,38 +41,6 @@
 #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.
-    have_futex = (sizeof (Atomic32) == sizeof (int) && 
-                  syscall(__NR_futex, &x, FUTEX_WAKE, 1, 0) >= 0);
-    if (have_futex &&
-        syscall(__NR_futex, &x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
-      futex_private_flag = 0;
-    }
-  }
-} init_module;
-
-}  // anonymous namespace
-
-
 namespace base {
 namespace internal {
 
@@ -81,28 +49,21 @@ void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
     int save_errno = errno;
     struct timespec tm;
     tm.tv_sec = 0;
-    if (have_futex) {
-      // Wait between 0-16ms.
-      tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
-      // Note: since Unlock() is optimized to not do a compare-and-swap,
-      // we can't expect explicit wake-ups. Therefore we shouldn't wait too
-      // long here.
-      syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
-                FUTEX_WAIT | futex_private_flag,
-                value, reinterpret_cast<struct kernel_timespec *>(&tm));
-    } else {
-      tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
-      nanosleep(&tm, NULL);
-    }
+    // Wait between 0-16ms.
+    tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
+    // Note: since Unlock() is optimized to not do a compare-and-swap,
+    // we can't expect explicit wake-ups. Therefore we shouldn't wait too
+    // long here.
+    syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
+            FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value,
+            reinterpret_cast<struct kernel_timespec*>(&tm));
     errno = save_errno;
   }
 }
 
 void SpinLockWake(volatile Atomic32 *w, bool all) {
-  if (have_futex) {
-    syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
-              FUTEX_WAKE | futex_private_flag, 1, 0);
-  }
+  syscall(__NR_futex, reinterpret_cast<int*>(const_cast<Atomic32*>(w)),
+          FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1, 0);
 }
 
 } // namespace internal