Segv when PDF-side JS object property getter invoked from XFA.

fpdfsdk/src/javascript/JS_Runtime.cpp

Index: fpdfsdk/src/javascript/JS_Runtime.cpp
diff --git a/fpdfsdk/src/javascript/JS_Runtime.cpp b/fpdfsdk/src/javascript/JS_Runtime.cpp
index 8b0475b85110d3c09d9325b6e499685372f0b5d9..9c2c6c6fed47073cb23092b764301e3c6d6aefae 100644
--- a/fpdfsdk/src/javascript/JS_Runtime.cpp
+++ b/fpdfsdk/src/javascript/JS_Runtime.cpp
@@ -245,12 +245,18 @@ FX_BOOL CJS_Runtime::GetHValueByName(const CFX_ByteStringC& utf8Name,
   v8::Locker lock(GetIsolate());
   v8::Isolate::Scope isolate_scope(GetIsolate());
   v8::HandleScope handle_scope(GetIsolate());
+  v8::Local<v8::Context> old_context = GetIsolate()->GetCurrentContext();
   v8::Local<v8::Context> context =
       v8::Local<v8::Context>::New(GetIsolate(), m_context);
   v8::Context::Scope context_scope(context);
 
-  // v8::Local<v8::Context> tmpCotext =
-  // v8::Local<v8::Context>::New(GetIsolate(), m_context);
+  // Caution: We're about to hand to XFA an object that may well require
+  // |context| to obtain this CJS_Runtime, but XFA will invoke against
+  // its own |old_context|, which has no CJS_Runtime. Associate ourselves
+  // with it at this point.

[jochen (gone - plz use gerrit), 2015/11/07 05:56:18]

i don't understand this comment?

[Tom Sepez, 2015/11/09 22:15:05]

Because the new XFA code and the old PDF code don't co-operate with each other
when invoking javascript, there are two (or more?) possible v8::Contexts that
are present -- one for each.  PDFium wants to access data from the current
contex'ts embedder data slot in order to figure out which document to operate
on.  This was set up by the PDF code.  The XFA code has no such pointer, so
whenever this code is invoked on top of a XFA-side v8::context, we store the
embedder data as if it were created by pdf.

+  // TODO(tsepez): redesign PDF-side objects to not rely on context.

[jochen (gone - plz use gerrit), 2015/11/07 05:56:18]

nor this

[Tom Sepez, 2015/11/09 22:15:05]

Changed.  Better?

+  FXJS_SetRuntimeForV8Context(old_context, this);
+
   v8::Local<v8::Value> propvalue =
       context->Global()->Get(v8::String::NewFromUtf8(
           GetIsolate(), name, v8::String::kNormalString, utf8Name.GetLength()));