On 2022-03-03 11:22, Stefan Hajnoczi wrote: > Hi, > The QEMU emulator uses coroutines with separate stacks. It can be > challenging to debug coroutines that have yielded because GDB is not > aware of them (no thread is currently executing them). > > QEMU has a GDB Python script that helps. It "creates" a stack frame for > a given coroutine by temporarily setting register values and then using > the "bt" command. This works on a live process under ptrace control but > not for coredumps where registers can't be set. > > Here is the script (or see the bottom of this email for an inline copy > of the relevant code): > https://gitlab.com/qemu-project/qemu/-/blob/master/scripts/qemugdb/coroutine.py > > I hoped that "select-frame address ADDRESS" could be used instead so > this would work on coredumps too. Unfortunately "select-frame" only > searches stack frames that GDB is already aware of, so it cannot be used > to backtrace coroutine stacks. > > Is there a way to backtrace a stack at an arbitrary address in GDB?
I don't think there's an easy/great answer. Maybe it could be done with a Python unwinder [1]? See gdb.python/py-unwind-user-regs.py in the GDB testsuite for an example you could probably start with. As for something built-in to GDB, this reminded me of a discussion a while ago around a "frame create" command. Here were my thoughts back then, I think still valid: https://sourceware.org/legacy-ml/gdb-patches/2015-09/msg00658.html [1] https://sourceware.org/gdb/onlinedocs/gdb/Unwinding-Frames-in-Python.html
