Bug 986673: Disable JIT signal tricks on demand, rather than all signaling; r=jandem

js/src/jit/AsmJS.cpp

@@ -6971,7 +6971,7 @@ EstablishPreconditions(ExclusiveContext *cx, AsmJSParser &parser)
     if (!cx->jitSupportsFloatingPoint())
         return Warn(parser, JSMSG_USE_ASM_TYPE_FAIL, "Disabled by lack of floating point support");
 
-    if (!cx->signalHandlersInstalled())
+    if (!cx->canUseSignalHandlers())
         return Warn(parser, JSMSG_USE_ASM_TYPE_FAIL, "Platform missing signal handler support");
 
     if (cx->gcSystemPageSize() != AsmJSPageSize)
@@ -7043,7 +7043,7 @@ js::IsAsmJSCompilationAvailable(JSContext *cx, unsigned argc, Value *vp)
 
     // See EstablishPreconditions.
     bool available = cx->jitSupportsFloatingPoint() &&
-                     cx->signalHandlersInstalled() &&
+                     cx->canUseSignalHandlers() &&
                      cx->gcSystemPageSize() == AsmJSPageSize &&
                      !cx->compartment()->debugMode() &&
                      cx->runtime()->options().asmJS();

js/src/jit/CompileWrappers.cpp

@@ -105,9 +105,9 @@ CompileRuntime::spsProfiler()
 }
 
 bool
-CompileRuntime::signalHandlersInstalled()
+CompileRuntime::canUseSignalHandlers()
 {
-    return runtime()->signalHandlersInstalled();
+    return runtime()->canUseSignalHandlers();
 }
 
 bool

js/src/jit/CompileWrappers.h

@@ -65,7 +65,7 @@ class CompileRuntime
     // Compilation does not occur off thread when the SPS profiler is enabled.
     SPSProfiler &spsProfiler();
 
-    bool signalHandlersInstalled();
+    bool canUseSignalHandlers();
     bool jitSupportsFloatingPoint();
     bool hadOutOfMemory();
     bool profilingScripts();

js/src/jit/Lowering.cpp

@@ -2214,7 +2214,7 @@ bool
 LIRGenerator::visitInterruptCheck(MInterruptCheck *ins)
 {
     // Implicit interrupt checks require asm.js signal handlers to be installed.
-    if (GetIonContext()->runtime->signalHandlersInstalled()) {
+    if (GetIonContext()->runtime->canUseSignalHandlers()) {
         LInterruptCheckImplicit *lir = new(alloc()) LInterruptCheckImplicit();
         return add(lir, ins) && assignSafepoint(lir, ins);
     }

js/src/jscntxt.h

@@ -277,7 +277,7 @@ struct ThreadSafeContext : ContextFriendFields,
     void *stackLimitAddress(StackKind kind) { return &runtime_->mainThread.nativeStackLimit[kind]; }
     void *stackLimitAddressForJitCode(StackKind kind);
     size_t gcSystemPageSize() { return gc::SystemPageSize(); }
-    bool signalHandlersInstalled() const { return runtime_->signalHandlersInstalled(); }
+    bool canUseSignalHandlers() const { return runtime_->canUseSignalHandlers(); }
     bool jitSupportsFloatingPoint() const { return runtime_->jitSupportsFloatingPoint; }
 
     // Thread local data that may be accessed freely.

js/src/vm/Runtime.cpp

@@ -189,6 +189,7 @@ JSRuntime::JSRuntime(JSRuntime *parentRuntime)
     haveCreatedContext(false),
     data(nullptr),
     signalHandlersInstalled_(false),
+    canUseSignalHandlers_(false),
     defaultFreeOp_(thisFromCtor(), false),
     debuggerMutations(0),
     securityCallbacks(const_cast<JSSecurityCallbacks *>(&NullSecurityCallbacks)),
@@ -257,6 +258,14 @@ JitSupportsFloatingPoint()
 #endif
 }
 
+static bool
+SignalBasedTriggersDisabled()
+{
+  // Don't bother trying to cache the getenv lookup; this should be called
+  // infrequently.
+  return !!getenv("JS_DISABLE_SLOW_SCRIPT_SIGNALS") || !!getenv("JS_NO_SIGNALS");
+}
+
 bool
 JSRuntime::init(uint32_t maxbytes, uint32_t maxNurseryBytes)
 {
@@ -338,6 +347,7 @@ JSRuntime::init(uint32_t maxbytes, uint32_t maxNurseryBytes)
 
 #ifdef JS_ION
     signalHandlersInstalled_ = EnsureAsmJSSignalHandlersInstalled(this);
+    canUseSignalHandlers_ = signalHandlersInstalled_ && !SignalBasedTriggersDisabled();
 #endif
 
     if (!spsProfiler.init())
@@ -546,14 +556,6 @@ JSRuntime::addSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf, JS::Runtim
 #endif
 }
 
-static bool
-SignalBasedTriggersDisabled()
-{
-  // Don't bother trying to cache the getenv lookup; this should be called
-  // infrequently.
-  return !!getenv("JS_DISABLE_SLOW_SCRIPT_SIGNALS");
-}
-
 void
 JSRuntime::requestInterrupt(InterruptMode mode)
 {
@@ -578,10 +580,8 @@ JSRuntime::requestInterrupt(InterruptMode mode)
      * asm.js and, optionally, normal Ion code use memory protection and signal
      * handlers to halt running code.
      */
-    if (!SignalBasedTriggersDisabled()) {
-        RequestInterruptForAsmJSCode(this, mode);
-        jit::RequestInterruptForIonCode(this, mode);
-    }
+    RequestInterruptForAsmJSCode(this, mode);
+    jit::RequestInterruptForIonCode(this, mode);
 #endif
 }
 

js/src/vm/Runtime.h

@@ -1072,14 +1072,20 @@ struct JSRuntime : public JS::shadow::Runtime,
     js::AsmJSMachExceptionHandler asmJSMachExceptionHandler;
 #endif
 
+  private:
     // Whether asm.js signal handlers have been installed and can be used for
     // performing interrupt checks in loops.
-  private:
     bool signalHandlersInstalled_;
+    // Whether we should use them or they have been disabled for making
+    // debugging easier. If signal handlers aren't installed, it is set to false.
+    bool canUseSignalHandlers_;
   public:
     bool signalHandlersInstalled() const {
         return signalHandlersInstalled_;
     }
+    bool canUseSignalHandlers() const {
+        return canUseSignalHandlers_;
+    }
 
   private:
     js::FreeOp          defaultFreeOp_;