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
  22 SignalTrampoline(int aSignal, siginfo_t* aInfo, void* aContext)
  23 {
  24   asm volatile (
  25     "nop; nop; nop; nop"
  26     : : : "memory");
  27
  28   // Because the assembler may generate additional insturctions below, we
  29   // need to ensure NOPs are inserted first by separating them out above.
  30
  31   asm volatile (
  32     "bx %0"
  33     :
  34     : "r"(H), "l"(aSignal), "l"(aInfo), "l"(aContext)
  35     : "memory");
  36 }
  37
  38 # define MOZ_SIGNAL_TRAMPOLINE(h) (mozilla::SignalTrampoline<h>)
  39
  40 #else // __arm__
  41
  42 # define MOZ_SIGNAL_TRAMPOLINE(h) (h)
  43
  44 #endif // __arm__
  45
  46 } // namespace mozilla
  47
  48 #endif // mozilla_LinuxSignal_h