Re: Cannot reverse debug

[Marc Petit-Huguenin]

Maybe someone can give some pointers on how to debug the problem here?

Thanks.

On 1/30/24 07:00, Marc Petit-Huguenin wrote:
> Hello,
> 
> I use Debian's QEMU 8.2.0+ds-5 and GDB 13.2-1 with a minimal kernel and an 
> initramfs containing just Busybox 1.36.1.  I record using the following 
> command line:
> 
> ....
> qemu-system-x86_64 \
> -display gtk \
> -icount shift=7,rr=record,rrfile=replay.bin \
> -drive file=vmstate.qcow2,if=none,snapshot=on,id=img \
> -drive driver=blkreplay,if=none,image=img,id=img-blkreplay \
> -device ide-hd,drive=img-blkreplay \
> -netdev user,id=net1,hostfwd=udp::1053-10.0.2.15:53 \
> -device e1000,netdev=net1 \
> -object filter-replay,id=replay,netdev=net1 \
> -kernel linux-source-6.6/arch/x86_64/boot/bzImage \
> -initrd initramfs.img \
> -append "console=ttyS0 root=/ init=/init"
> ....
> 
> I then replay using the following command line:
> 
> ....
> qemu-system-x86_64 \
> -s \
> -S \
> -display gtk \
> -icount shift=10,rr=replay,rrfile=replay.bin \
> -drive file=vmstate.qcow2,if=none,snapshot=on,id=img \
> -drive driver=blkreplay,if=none,image=img,id=img-blkreplay \
> -device ide-hd,drive=img-blkreplay \
> -netdev user,id=net1,hostfwd=udp::1053-10.0.2.15:53 \
> -device e1000,netdev=net1 \
> -object filter-replay,id=replay,netdev=net1 \
> -kernel linux-source-6.6/arch/x86_64/boot/bzImage \
> -initrd initramfs.img \
> -append "console=ttyS0 root=/ init=/init"
> ....
> 
> I then connect gdb, install two breakpoints in user space, and continue the 
> execution.  The code is executed until the first breakpoint.  I continue, and 
> the code is executed until the second breakpoint.  So far so good.
> 
> Then I execute reverse-continue, but the code never goes back to the first 
> breakpoint.  `info replay` is stuck with:
> 
> Replaying execution 'replay.bin': instruction count = 0
> 
> What am I doing wrong?
> 

-- 
Marc Petit-Huguenin
Email: marc@petit-huguenin.org
Blog: https://marc.petit-huguenin.org
Profile: https://www.linkedin.com/in/petithug

OpenPGP_signature.asc
Description: OpenPGP digital signature