Commit 772f86839f ("scripts/qemu-gdb: Support coroutine dumps in
coredumps") introduced coroutine traces in coredumps using raw stack
unwinding. While this works, this approach does not allow to view the
function arguments in the corresponding stack frames.
As an alternative, we can obtain saved registers from the coroutine's
jmpbuf, patch them into the coredump's struct elf_prstatus in place, and
execute another gdb subprocess to get backtrace from the patched temporary
coredump.
While providing more detailed info, this alternative approach, however, is
more invasive as it might potentially corrupt the coredump file. We do take
precautions by saving the original registers values into a separate binary
blob /path/to/coredump.ptregs, so that it can be restores in the next
GDB session. Still, instead of making it a new deault, let's keep raw unwind
the default behaviour, but add the '--detailed' option for 'qemu bt' and
'qemu coroutine' command which would enforce the new behaviour.
That's how this looks:
(gdb) qemu coroutine 0x7fda9335a508
#0 0x5602bdb41c26 in qemu_coroutine_switch<+214> () at ../util/coroutine-ucontext.c:321
#1 0x5602bdb3e8fe in qemu_aio_coroutine_enter<+493> () at ../util/qemu-coroutine.c:293
#2 0x5602bdb3c4eb in co_schedule_bh_cb<+538> () at ../util/async.c:547
#3 0x5602bdb3b518 in aio_bh_call<+119> () at ../util/async.c:172
#4 0x5602bdb3b79a in aio_bh_poll<+457> () at ../util/async.c:219
#5 0x5602bdb10f22 in aio_poll<+1201> () at ../util/aio-posix.c:719
#6 0x5602bd8fb1ac in iothread_run<+123> () at ../iothread.c:63
#7 0x5602bdb18a24 in qemu_thread_start<+355> () at ../util/qemu-thread-posix.c:393
(gdb) qemu coroutine 0x7fda9335a508 --detailed
patching core file /tmp/tmpq4hmk2qc
found "CORE" at 0x10c48
assume pt_regs at 0x10cbc
write r15 at 0x10cbc
write r14 at 0x10cc4
write r13 at 0x10ccc
write r12 at 0x10cd4
write rbp at 0x10cdc
write rbx at 0x10ce4
write rip at 0x10d3c
write rsp at 0x10d54
#0 0x00005602bdb41c26 in qemu_coroutine_switch (from_=0x7fda9335a508, to_=0x7fda8400c280, action=COROUTINE_ENTER) at ../util/coroutine-ucontext.c:321
#1 0x00005602bdb3e8fe in qemu_aio_coroutine_enter (ctx=0x5602bf7147c0, co=0x7fda8400c280) at ../util/qemu-coroutine.c:293
#2 0x00005602bdb3c4eb in co_schedule_bh_cb (opaque=0x5602bf7147c0) at ../util/async.c:547
#3 0x00005602bdb3b518 in aio_bh_call (bh=0x5602bf714a40) at ../util/async.c:172
#4 0x00005602bdb3b79a in aio_bh_poll (ctx=0x5602bf7147c0) at ../util/async.c:219
#5 0x00005602bdb10f22 in aio_poll (ctx=0x5602bf7147c0, blocking=true) at ../util/aio-posix.c:719
#6 0x00005602bd8fb1ac in iothread_run (opaque=0x5602bf42b100) at ../iothread.c:63
#7 0x00005602bdb18a24 in qemu_thread_start (args=0x5602bf7164a0) at ../util/qemu-thread-posix.c:393
#8 0x00007fda9e89f7f2 in start_thread (arg=<optimized out>) at pthread_create.c:443
#9 0x00007fda9e83f450 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: Peter Xu <peterx@redhat.com>
Originally-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20251204105019.455060-5-andrey.drobyshev@virtuozzo.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Andrey Drobyshev