mfbt/LinuxSignal.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_LinuxSignal_h
   6 #define mozilla_LinuxSignal_h
   7
   8 namespace mozilla {
   9
  10 #if defined(__arm__)
  11
  12 // Some (old) Linux kernels on ARM have a bug where a signal handler
  13 // can be called without clearing the IT bits in CPSR first. The result
  14 // is that the first few instructions of the handler could be skipped,
  15 // ultimately resulting in crashes. To workaround this bug, the handler
  16 // on ARM is a trampoline that starts with enough NOP instructions, so
  17 // that even if the IT bits are not cleared, only the NOP instructions
  18 // will be skipped over.
  19
  20 template <void (*H)(int, siginfo_t*, void*)>
  21 __attribute__((naked)) void SignalTrampoline(int aSignal, siginfo_t* aInfo,
  22                                              void* aContext) {
  23   asm volatile("nop; nop; nop; nop" : : : "memory");
  24
  25   asm volatile("b %0" : : "X"(H) : "memory");
  26 }
  27
  28 #  define MOZ_SIGNAL_TRAMPOLINE(h) (mozilla::SignalTrampoline<h>)
  29
  30 #else  // __arm__
  31
  32 #  define MOZ_SIGNAL_TRAMPOLINE(h) (h)
  33
  34 #endif  // __arm__
  35
  36 }  // namespace mozilla
  37
  38 #endif  // mozilla_LinuxSignal_h