Currently, VM entry points in Interpreter.cpp calls JSStack::entryCheck() ensure adequate capacity on the JSStack before re-entering the VM. We can eliminate this if we implement allow for a red zone in the JSStack.
Let's call this the "host zone", to distinguish from the OS-provided redzone, which is for leaf functions.
It's a bit difficult to get this right with the JSStack internal pointers sometime pointing to the top of stack and sometimes pointing past the end of the stack. To make the code more sane to reason about, I will first fix https://bugs.webkit.org/show_bug.cgi?id=125849 before returning to this bug.
This was fixed in r161927: <http://trac.webkit.org/r161927> which was committed for https://bugs.webkit.org/show_bug.cgi?id=126790. *** This bug has been marked as a duplicate of bug 126790 ***