- Do not allocate a new stack, if the thread already has a large one. This prevents the function from freeing a large stack as a normal stack and subsequently leaking system PTEs.
- Fix the check for failure of PsConvertToGuiThread (test eax, not rax, for being negative, because by default rax is zero extended from eax, not sign extended). This fixes an infinite loop on failure.
KiSetTrapContext is an asm wrapper around RtlSetUnwindContext, which first stores an exception frame to assure that all non-volatile registers were put on the stack, then calls RtlSetUnwindContext to update their first saving positions on the stack and finally restore the exception frame to potentially load any updated registers, that haven't been saved elsewhere on the stack.
