Backed out changeset 98e368b5c4be (bug 1463035) for failures in tools/profiler/tests/chrome/test_profile_worker.html on a CLOSED TREE

mfbt/LinuxSignal.h

@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_LinuxSignal_h
+#define mozilla_LinuxSignal_h
+
+namespace mozilla {
+
+#if defined(__arm__)
+
+// Some (old) Linux kernels on ARM have a bug where a signal handler
+// can be called without clearing the IT bits in CPSR first. The result
+// is that the first few instructions of the handler could be skipped,
+// ultimately resulting in crashes. To workaround this bug, the handler
+// on ARM is a trampoline that starts with enough NOP instructions, so
+// that even if the IT bits are not cleared, only the NOP instructions
+// will be skipped over.
+
+template <void (*H)(int, siginfo_t*, void*)>
+__attribute__((naked)) void
+SignalTrampoline(int aSignal, siginfo_t* aInfo, void* aContext)
+{
+  asm volatile (
+    "nop; nop; nop; nop"
+    : : : "memory");
+
+  asm volatile (
+    "b %0"
+    :
+    : "X"(H)
+    : "memory");
+}
+
+# define MOZ_SIGNAL_TRAMPOLINE(h) (mozilla::SignalTrampoline<h>)
+
+#else // __arm__
+
+# define MOZ_SIGNAL_TRAMPOLINE(h) (h)
+
+#endif // __arm__
+
+} // namespace mozilla
+
+#endif // mozilla_LinuxSignal_h

mfbt/moz.build

@@ -122,6 +122,10 @@ if CONFIG['OS_ARCH'] == 'WINNT':
     EXPORTS.mozilla += [
         'WindowsVersion.h',
     ]
+elif CONFIG['OS_ARCH'] == 'Linux':
+    EXPORTS.mozilla += [
+        'LinuxSignal.h',
+    ]
 
 UNIFIED_SOURCES += [
     'Assertions.cpp',

tools/profiler/core/platform-linux-android.cpp

@@ -60,6 +60,7 @@
 #include <stdarg.h>
 
 #include "prenv.h"
+#include "mozilla/LinuxSignal.h"
 #include "mozilla/PodOperations.h"
 #include "mozilla/DebugOnly.h"
 
@@ -276,7 +277,7 @@ Sampler::Sampler(PSLockRef aLock)
 
   // Request profiling signals.
   struct sigaction sa;
-  sa.sa_sigaction = SigprofHandler;
+  sa.sa_sigaction = MOZ_SIGNAL_TRAMPOLINE(SigprofHandler);
   sigemptyset(&sa.sa_mask);
   sa.sa_flags = SA_RESTART | SA_SIGINFO;
   if (sigaction(SIGPROF, &sa, &mOldSigprofHandler) != 0) {