> From: Markus Armbruster [mailto:email@example.com] > Kevin Wolf <firstname.lastname@example.org> writes: > > > Am 09.01.2020 um 07:13 hat Pavel Dovgalyuk geschrieben: > >> Ping. > > > > I think you have my Acked-by for the block-related patches in this > > series now. If I missed something, please let me know. > > Pavel, whom are you nudging to do what? I'm not sure. My prior patches for record/replay were pulled by Paolo. But reverse debugging is more like a modification of things, and not a completely new subsystem. Everything but gdbstub was already acked by the maintainers. Pavel Dovgalyuk
> From: Alex Bennée [mailto:email@example.com] > Pavel Dovgalyuk <firstname.lastname@example.org> writes: > > > GDB remote protocol supports reverse debugging of the targets. > > It includes 'reverse step' and 'reverse continue' operations. > > The first one finds the previous step of the execution, > > and the second one is intended to stop at the last breakpoint that > > would happen when the program is executed normally. > > > > Reverse debugging is possible in the replay mode, when at least > > one snapshot was created at the record or replay phase. > > QEMU can use these snapshots for travelling back in time with GDB. > > > > Running the execution in replay mode allows using GDB reverse debugging > > commands: > > - reverse-stepi (or rsi): Steps one instruction to the past. > > QEMU loads on of the prior snapshots and proceeds to the desired > > instruction forward. When that step is reaches, execution stops. > > - reverse-continue (or rc): Runs execution "backwards". > > QEMU tries to find breakpoint or watchpoint by loaded prior snapshot > > and replaying the execution. Then QEMU loads snapshots again and > > replays to the latest breakpoint. When there are no breakpoints in > > the examined section of the execution, QEMU finds one more snapshot > > and tries again. After the first snapshot is processed, execution > > stops at this snapshot. > > > > The set of patches include the following modifications: > > - gdbstub update for reverse debugging support > > - functions that automatically perform reverse step and reverse > > continue operations > > - hmp/qmp commands for manipulating the replay process > > - improvement of the snapshotting for saving the execution step > > in the snapshot parameters > > > > The patches are available in the repository: > > https://github.com/ispras/qemu/tree/rr-191223 > > So I tried with your additional patch. Launching QEMU as: > > ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ > -display none -M virt -cpu max -display none \ > -semihosting-config enable=on \ > -kernel ./tests/tcg/aarch64-softmmu/memory \ > -icount shift=5,rr=replay,rrfile=record.bin \ > -s -S -d trace:gdbstub\* > > And gdb: > > gdb tests/tcg/aarch64-softmmu/memory \ > -ex "target remote localhost:1234" > > I get the following log: > > (gdb) x/3i $pc > => 0x400037b0 <__start>: adr x0, 0x40003000 <vector_table> > 0x400037b4 <__start+4>: msr vbar_el1, x0 > 0x400037b8 <__start+8>: adrp x0, 0x40200000 > (gdb) p/x $x0 > $1 = 0x0 > (gdb) si > 92 msr vbar_el1, x0 > (gdb) p/x $x0 > $2 = 0x40003000 > (gdb) rsi > warning: Remote failure reply: E14 > > Program stopped. > __start () at /home/alex.bennee/lsrc/qemu.git/tests/tcg/aarch64/system/boot.S:92 > 92 msr vbar_el1, x0 > (gdb) p/x $x0 > $3 = 0x40003000 > > So it doesn't seem to be working. That's ok, you'll need at least one VM snapshot available to recover the initial VM state. Try changing the command lines in the following way: First, create empty.qcow2 which will be used for saving the snapshots. Then record with initial snapshot and attached empty.qcow2: ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ -display none -M virt -cpu max \ -kernel ./tests/tcg/aarch64-softmmu/memory \ -icount shift=5,rr=record,rrfile=record.bin,rrsnapshot=init \ -drive file=empty.qcow2 After that you can replay the execution with the support of reverse debugging: ./aarch64-softmmu//qemu-system-aarch64 -monitor none \ -display none -M virt -cpu max \ -kernel ./tests/tcg/aarch64-softmmu/memory \ -icount shift=5,rr=replay,rrfile=record.bin,rrsnapshot=init \ -drive file=empty.qcow2 I removed "-semihosting-config enable=on", because I'm not sure what is it for. It may break the replay, because there is no implementation of semihosting input record/replay. Pavel Dovgalyuk
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