Work around a kernel bug on Android.

runtime/vm/signal_handler.h

Index: runtime/vm/signal_handler.h
diff --git a/runtime/vm/signal_handler.h b/runtime/vm/signal_handler.h
index b204c55d55f1b127f781fc8c73b8c50989861b3d..9f1ef93288ca51662bbc4160197441c921bfa6cc 100644
--- a/runtime/vm/signal_handler.h
+++ b/runtime/vm/signal_handler.h
@@ -36,6 +36,16 @@ struct sigset_t {
 };
 #endif
 
+
+// Old linux kernels on ARM might require a trampoline to
+// work around incorrect Thumb -> ARM transitions. See SignalHandlerTrampoline
+// below for more details.
+#if defined(HOST_ARCH_ARM) && \

[Florian Schneider, 2016/05/02 14:43:43]

s/HOST_ARCH_ARM/TARGET_ARCH_ARM/

[zra, 2016/05/02 15:53:54]

I think HOST might be right since we don't want this code in simarm.

+    (defined(TARGET_OS_LINUX) || defined(TARGET_OS_ANDROID))
+#define USE_SIGNAL_HANDLER_TRAMPOLINE
+#endif
+
+
 namespace dart {
 
 typedef void (*SignalAction)(int signal, siginfo_t* info,
@@ -43,17 +53,68 @@ typedef void (*SignalAction)(int signal, siginfo_t* info,
 
 class SignalHandler : public AllStatic {
  public:
-  static void Install(SignalAction action);
+  template<SignalAction action>
+  static void Install() {
+#if defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
+    InstallImpl(SignalHandlerTrampoline<action>);
+#else
+    InstallImpl(action);
+#endif  // defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
+  }
   static void Remove();
   static uintptr_t GetProgramCounter(const mcontext_t& mcontext);
   static uintptr_t GetFramePointer(const mcontext_t& mcontext);
   static uintptr_t GetCStackPointer(const mcontext_t& mcontext);
   static uintptr_t GetDartStackPointer(const mcontext_t& mcontext);
   static uintptr_t GetLinkRegister(const mcontext_t& mcontext);
+
  private:
+  static void InstallImpl(SignalAction action);
+
+#if defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
+  // Work around for a bug in old kernels (only fixed in 3.18 Android kernel):
+  //
+  // Kernel does not clear If-Then execution state bits when entering ARM signal
+  // handler which violates requirements imposed by ARM architecture reference.
+  // Some CPUs look at these bits even while in ARM mode which causes them
+  // to skip some instructions in the prologue of the signal handler.
+  //
+  // To work around the issue we insert enough NOPs in the prologue to ensure
+  // that no actual instructions are skipped and then branch to the actual
+  // signal handler.
+  //
+  // For the kernel patch that fixes the issue see: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ecf830e5029598732e04067e325d946097519cb
+  //
+  // Note: this function is marked "naked" because we must guarantee that
+  // our NOPs occur before any compiler generated prologue.
+  template <SignalAction action>
+  static __attribute__((naked)) void SignalHandlerTrampoline(int signal,
+                                                             siginfo_t* info,
+                                                             void* context_) {
+    // IT (If-Then) instruction makes up to four instructions that follow it
+    // conditional.
+    asm volatile("nop; nop; nop; nop" : : : "memory");
+
+    // Tail-call into the actual signal handler.
+    // Note: this code is split into a separate inline assembly block because
+    // any code that compiler generates to satisfy register constraints must
+    // be generated after four NOPs.
+    register int arg0 asm("r0") = signal;
+    register siginfo_t* arg1 asm("r1") = info;
+    register void* arg2 asm("r2") = context_;
+    asm volatile("bx %3"
+                  :
+                  : "r"(arg0), "r"(arg1), "r"(arg2),
+                    "r"(action)
+                  : "memory");
+  }
+#endif  // defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
 };
 
 
+#undef USE_SIGNAL_HANDLER_TRAMPOLINE
+
+
 }  // namespace dart
 
 #endif  // VM_SIGNAL_HANDLER_H_