In general, there's no difference between the stack of the C++ program and the stack of the JS program. When SpiderMonkey just-in-time compiles a JS function, t

In general, there's no difference between the stack of the C++ program and the stack of the JS program. When SpiderMonkey just-in-time compiles a JS function, the result is native code that creates a stack frame on the same stack as the C++ code that implements SpiderMonkey. JS code and C++ code can be semi-arbitrarily interleaved on the stack: JS calls C++ calls JS calls C++... The one exception about sharing the same stack is that the first few iterations of a function run in an interpreter implemented in C++, and that interpreter has its own stack that we heap-allocate. This particular bug occurred during the transition from the C++ interpreter to JIT code.