Messages in this thread | | | From | Linus Torvalds <> | Date | Sun, 20 Jun 2021 20:37:22 -0700 | Subject | Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch_stack |
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On Sun, Jun 20, 2021 at 8:18 PM Michael Schmitz <schmitzmic@gmail.com> wrote: > > I hope that makes more sense?
So the problem is in your debug patch: you don't set that TIS_SWITCH_STACK in nearly enough places.
In this particular example, I think it's that you don't set it in do_trace_exit, so when you strace the process, the system call exit - which is where the return value will be picked up - gets that warning.
You did set TIS_SWITCH_STACK on trace_entry, but then it's cleared again during the system call, and not set at the trace_exit path. Oddly, your debug patch also _clears_ it on the exit path, but it doesn't set it when do_trace_exit does the SAVE_SWITCH_STACK.
You oddly also set it for __sys_exit, but not all the other special system calls that also do that SAVE_SWITCH_STACK.
Really, pretty much every single case of SAVE_SWITCH_STACK would need to set it. Not just do_trace_enter/exit
It's why I didn't like Eric's debug patch either. It's quite expensive to do, partly because you look up that curptr thing. All very nasty.
It would be *much* better to make the flag be part of the stack frame, but sadly at least on alpha we had exported the format of that stack frame to user space.
Anyway, I think these debug patches are not just expensive but the m68k one most definitely is also very incomplete.
Linus
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