[wasm] Acquire the context for TrapIf from a wasm frame

src/runtime/runtime-wasm.cc

Index: src/runtime/runtime-wasm.cc
diff --git a/src/runtime/runtime-wasm.cc b/src/runtime/runtime-wasm.cc
index d7e1dba54f7f18f10946e1397c49e064d707c1c0..285b0210879dc875fd409455bf91ef82547a4256 100644
--- a/src/runtime/runtime-wasm.cc
+++ b/src/runtime/runtime-wasm.cc
@@ -55,6 +55,14 @@ RUNTIME_FUNCTION(Runtime_WasmGrowMemory) {
 Object* ThrowRuntimeError(Isolate* isolate, int message_id, int byte_offset,

[Michael Starzinger, 2017/02/01 11:36:52]

We could add a DCHECK_NULL(isolate->context()) here to ensure callers adhere to
the convention. We do something similar in Runtime_NotifyDeoptimized already,
where we also call {Isolate::set_context} in a similar fashion.

[ahaas, 2017/02/01 11:48:51]

Done.

                           bool patch_source_position) {
   HandleScope scope(isolate);
+  StackFrameIterator it(isolate);
+  it.Advance();
+  DCHECK(!it.done());
+  DCHECK(it.frame()->is_wasm());

[Clemens Hammacher, 2017/01/31 19:20:33]

If this is just DCHECKs, we can actually skip them, because
StackFrameIterator::frame already DCHECKs !done(), and WasmCompiledFrame::cast
checks the frame type.

[ahaas, 2017/02/01 11:48:51]

I removed the DCHECK(!it.done()); and added
CHECK(it.frame()->is_wasm_compiled());

+  isolate->set_context(*WasmCompiledFrame::cast(it.frame())

[titzer, 2017/01/31 19:16:08]

We should be careful here. I assume that Throw() below will reset the context,
but I'm not entirely sure.

[Clemens Hammacher, 2017/01/31 19:20:33]

I am still not sure if it's really needed, but to be on the save side, we should
use a SaveContext here.

[Michael Starzinger, 2017/02/01 11:36:52]

AFAICT the {Throw} method itself should not change the current context. What
will change the current context though is the CEntryStub during the stack
unwinding after this function returns. This unwinding itself should not inspect
the current context. So at first glance this looks safe to me.

+                            ->wasm_instance()
+                            ->compiled_module()
+                            ->native_context());
   Handle<Object> error_obj = isolate->factory()->NewWasmRuntimeError(
       static_cast<MessageTemplate::Template>(message_id));