[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB
From: |
Alex Bennée |
Subject: |
Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB |
Date: |
Fri, 17 Jan 2020 17:40:06 +0000 |
User-agent: |
mu4e 1.3.6; emacs 28.0.50 |
Pavel Dovgalyuk <address@hidden> writes:
>> From: Alex Bennée [mailto:address@hidden]
>> Pavel Dovgalyuk <address@hidden> 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
./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=record,rrfile=record.bin,rrsnapshot=init -drive file=empty.qcow2
qemu-system-aarch64: invalid accelerator kvm
qemu-system-aarch64: falling back to tcg
qemu-system-aarch64: The qcow format used by node '#block163' does not support
live migration
qemu-system-aarch64: Could not create snapshot for icount record
I don't know if this is down to the current state of the tree but I
haven't been able to get it working.
>
> 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.
For this testcase semihosting in just a convenient output device (in
lieu of a serial device). We probably need to come up with a strategy on
how we handle all these devices otherwise we will end up with a random
selection of hardware combinations which work.
>
> Pavel Dovgalyuk
--
Alex Bennée
- RE: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, (continued)
- RE: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Pavel Dovgalyuk, 2020/01/09
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Markus Armbruster, 2020/01/13
- RE: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Pavel Dovgalyuk, 2020/01/13
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Kevin Wolf, 2020/01/13
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Peter Maydell, 2020/01/13
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Kevin Wolf, 2020/01/13
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Peter Maydell, 2020/01/13
- Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Alex Bennée, 2020/01/13
Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB, Alex Bennée, 2020/01/16