Re: [Qemu-devel] [PATCH v4 00/19] reverse debugging

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:
> 
> >> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> >> Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:
> >>
> >> >> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> >> >> Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru> writes:
> >> >>
> >> >> > Ping?
> >> >>
> >> >> I started having a look but I ran into this straight away. First I
> >> >> recorded a boot of the kernel:
> >> >>
> >> >>   ./aarch64-softmmu/qemu-system-aarch64 -machine virt,graphics=on,gic-
> >> >> version=3,virtualization=on -cpu cortex-a53 --serial mon:stdio -display none -kernel
> >> >> ../images/aarch64-current-linux-initrd-guest.img -icount
> >> shift=7,rr=record,rrfile=replay.bin
> >> >>
> >> >> Then played back:
> >> >>
> >> >>   ./aarch64-softmmu/qemu-system-aarch64 -machine virt,graphics=on,gic-
> >> >> version=3,virtualization=on -cpu cortex-a53 --serial mon:stdio -display none -kernel
> >> >> ../images/aarch64-current-linux-initrd-guest.img -icount
> >> shift=7,rr=replay,rrfile=replay.bin -
> >> >> s -S
> >> >
> >> > This looks ok, but...
> >> >
> >> >> And did the following on gdb:
> >> >>
> >> >> (gdb) i
> >> >> 0x0000000040000004 in ?? ()
> >> >> => 0x40000004:  mov     x1, xzr
> >> >>    0x40000008:  mov     x2, xzr
> >> >>    0x4000000c:  mov     x3, xzr
> >> >> (gdb)
> >> >> 0x0000000040000008 in ?? ()
> >> >> => 0x40000008:  mov     x2, xzr
> >> >>    0x4000000c:  mov     x3, xzr
> >> >>    0x40000010:  ldr     x4, 0x40000020
> >> >> (gdb)
> >> >> 0x000000004000000c in ?? ()
> >> >> => 0x4000000c:  mov     x3, xzr
> >> >>    0x40000010:  ldr     x4, 0x40000020
> >> >>    0x40000014:  br      x4
> >> >> (gdb)
> >> >> 0x0000000040000010 in ?? ()
> >> >> => 0x40000010:  ldr     x4, 0x40000020
> >> >>    0x40000014:  br      x4
> >> >>    0x40000018:  .inst   0x44000000 ; undefined
> >> >> (gdb)
> >> >> 0x0000000040000014 in ?? ()
> >> >> => 0x40000014:  br      x4
> >> >>    0x40000018:  .inst   0x44000000 ; undefined
> >> >>    0x4000001c:  .inst   0x00000000 ; undefined
> >> >> (gdb) p/x $x4
> >> >> $1 = 0x40080000
> >> >> (gdb) reverse-stepi
> >> >> warning: Remote failure reply: E14
> >> >>
> >> >> Surely this is the simple case and doesn't require any snapshots for
> >> >> block devices as there are none. Am I missing something?
> >> >
> >> > Reverse debugging requires the snapshotting. QEMU can't revert the VM state without the
> >> snapshots.
> >> > You can try adding an empty qcow2 image to allow snapshotting there.
> >>
> >> I suspect a recent patch has broken locking again:
> >>
> >> Starting program: /home/alex/lsrc/qemu/qemu.git/aarch64-softmmu/qemu-system-aarch64 -
> machine
> >> virt,graphics=on,gic-version=3,virtualization=on -cpu cortex-a53 --serial mon:stdio -
> display
> >> none -kernel ../images/aarch64-current-linux-initrd-guest.img -icount
> >> shift=7,rr=replay,rrfile=replay.bin,rrsnapshot=debug -drive
> >> file=rr.qcow2,if=none,snapshot,id=rr -s -S
> >> [Thread debugging using libthread_db enabled]
> >> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
> >> [New Thread 0x7fffd8536700 (LWP 32452)]
> >> [New Thread 0x7fffd5bb3700 (LWP 32453)]
> >> [New Thread 0x7fffd4eab700 (LWP 32454)]
> >> **
> >> ERROR:replay/replay-time.c:49:replay_read_clock: assertion failed: (replay_file &&
> >> replay_mutex_locked())
> >
> > Have you recorded it with the attached disk before replaying?
> 
> Yes. I assume the -drive doesn't actually have to be visible to the
> guest, it's just the mechanism rr needs for saving snapshots?
> 
> > Are you using the latest version?
> > If the both answers are 'yes', then can you share the kernel? My i386
> > runs work normally.
> 
> I'll have a go with x86 first as aarch64 hasn't been proven yet.

Any news about that?


Pavel Dovgalyuk