From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: Changbin Du <changbin.du@gmail.com>,
Luc Michel <luc.michel@greensocs.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
alex.bennee@linaro.org, qemu-devel@nongnu.org
Subject: Re: [PATCH] tcg: gdbstub: Fix single-step issue on arm target
Date: Fri, 21 Feb 2020 13:33:17 +0100 [thread overview]
Message-ID: <d50a811f-ea55-c6cb-f144-8279b2867c72@redhat.com> (raw)
In-Reply-To: <20200221115104.x3af4cfjin553jun@mail.google.com>
On 2/21/20 12:51 PM, Changbin Du wrote:
> On Thu, Feb 20, 2020 at 10:24:37PM +0100, Luc Michel wrote:
>> I'm curious, I never experienced this behaviour from GDB. What GDB and
>> QEMU versions are you using?
>>
>> On my side (GDB 9.1), even without 'vContSupported+' in the 'qSupported'
>> answer, GDB sends a 'vCont?' packet on the first stepi:
>>
>> 0x00000000 in ?? ()
>> (gdb) si
>> Sending packet: $m0,4#fd...Ack
>> Packet received: 00000000
>> Sending packet: $vCont?#49...Ack
>> Packet received: vCont;c;C;s;S
>> Packet vCont (verbose-resume) is supported
>> Sending packet: $vCont;s:p1.1;c:p1.-1#f7...Ack
>> Packet received: T05thread:p01.01;
>>
>> Your second issue (wrong PC value) should be investigated though. Does
>> it happen on QEMU vanilla? Do you have a way to reproduce this bug?
>>
> Just confirmed this issue. This is an endianness problem for gdb. I was
> debugging an big-endian elf and my host cpu is little-endian. QEMU gdbstub
> always uses host cpu endian but gdb client treats it as big-endian by
> inspecting elf info.
I'm using Debian gdb-multiarch, and indeed use cross-endianess (I always
set arch/endian explicitly). This might be why I hit this too.
>
> I can mannually set it to little-endian but it is painful. The gdb complains
> abount invalid opcode error in debuginfo.
>
> I also noticed that someoneelse has already tried to resolve this issue.
> https://patchwork.kernel.org/patch/9528947/
>
>> Anyway after re-reading the GDB remote protocol documentation, I think
>> your patch is right, the feature should be advertised.
>>
>> However I think your commit message needs some modifications. This fix
>> is not specific to ARM or TCG, but to the gdbstub itself. You also
>> mention this bug you have with PC, which is not related to the bug you
>> are fixing here. Could you rewrite it in a more generic way? You simply
>> need to emphasis the effect of advertising the 'vContSupported+' feature
>> on GDB.
>>
>> Thanks.
>>
>> --
>> Luc
>
prev parent reply other threads:[~2020-02-21 12:34 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 15:58 [PATCH] tcg: gdbstub: Fix single-step issue on arm target Changbin Du
2020-02-20 17:47 ` Philippe Mathieu-Daudé
2020-02-20 18:06 ` Laurent Vivier
2020-02-20 18:55 ` Philippe Mathieu-Daudé
2020-02-21 0:08 ` Changbin Du
2020-02-20 17:58 ` Peter Maydell
2020-02-20 21:24 ` Luc Michel
2020-02-21 0:07 ` Changbin Du
2020-02-21 11:51 ` Changbin Du
2020-02-21 12:33 ` Philippe Mathieu-Daudé [this message]
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