On 8/3/23 14:06, Peter Zijlstra wrote:
By marking them with STACK_FRAME_NON_STANDARD you will get no ORC data at all, and then you also violate the normal framepointer calling convention. This means that if you need to unwind here you're up a creek without no paddles on.
The only weird thing that can happen is ud2 instructions that are executed in case the vmload/vmrun/vmsave instructions causes a #GP, from the exception handler.
If I understand correctly those ud2 would use ORC information to show the backtrace, but even then the frame pointer should be correct. Of these instructions, vmrun is the only one that runs with wrong %rbp; and it is unlikely or even impossible that a #GP happens at vmrun, because the same operand has been used for a vmload ten instructions before. The only time I saw that #GP it was due to a processor errata, but it happened consistently on the vmload.
So if frame pointer unwinding can be used in the absence of ORC, Nikunj patch should not break anything.
Paolo
