author Mike Hommey <>
Wed, 20 Mar 2019 09:07:16 +0000
changeset 465194 a8e6586172fdefe46349797d8aef9cc5e7147d3b
parent 454520 5f4630838d46dd81dadb13220a4af0da9e23a619
permissions -rw-r--r--
Bug 1434526 - Make MOZ_SIGNAL_TRAMPOLINE Android-only. r=gsvelto Bug 1463035 exists to remove it entirely, because as mentioned in bug 1238661 comment 4, we don't actually need this workaround anymore. But that bug has been blocked for a while because the Android emulator images we use for testing, for some reason, use a kernel older than any real device using the same version of Android would use. Let's however fix the problems it causes with GCC on non-Android ARM Linux by making it Android-only, rather than removing it entirely. Differential Revision:

/* 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 */

#ifndef mozilla_LinuxSignal_h
#define mozilla_LinuxSignal_h

namespace mozilla {

#if defined(__arm__) && defined(__ANDROID__)

// 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