From: Changbin Du <changbin.du@gmail.com>
To: Changbin Du <changbin.du@gmail.com>
Cc: philmd@redhat.com, alex.bennee@linaro.org, qemu-devel@nongnu.org
Subject: Re: [PATCH v2] gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb
Date: Mon, 9 Mar 2020 10:43:23 +0000 [thread overview]
Message-ID: <20200309104322.u6ktpdl5yjdfcvqa@mail.google.com> (raw)
In-Reply-To: <20200221002559.6768-1-changbin.du@gmail.com>
hello, is this patch ready to merge now? Thanks!
On Fri, Feb 21, 2020 at 08:25:59AM +0800, Changbin Du wrote:
> Recently when debugging an arm32 system on qemu, I found sometimes the
> single-step command (stepi) is not working. This can be reproduced by
> below steps:
> 1) start qemu-system-arm -s -S .. and wait for gdb connection.
> 2) start gdb and connect to qemu. In my case, gdb gets a wrong value
> (0x60) for PC, which is an another bug.
> 3) After connected, type 'stepi' and expect it will stop at next ins.
>
> But, it has never stopped. This because:
> 1) We doesn't report ‘vContSupported’ feature to gdb explicitly and gdb
> think we do not support it. In this case, gdb use a software breakpoint
> to emulate single-step.
> 2) Since gdb gets a wrong initial value of PC, then gdb inserts a
> breakpoint to wrong place (PC+4).
>
> Not only for the arm target, Philippe has also encountered this on MIPS.
> Probably gdb has different assumption for different architectures.
>
> Since we do support ‘vContSupported’ query command, so let's tell gdb that
> we support it.
>
> Before this change, gdb send below 'Z0' packet to implement single-step:
> gdb_handle_packet: Z0,4,4
>
> After this change, gdb send "vCont;s.." which is expected:
> gdb_handle_packet: vCont?
> put_packet: vCont;c;C;s;S
> gdb_handle_packet: vCont;s:p1.1;c:p1.-1
>
> Signed-off-by: Changbin Du <changbin.du@gmail.com>
> Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>
> ---
> v2: polish commit message.
> ---
> gdbstub.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdbstub.c b/gdbstub.c
> index ce304ff482..adccd938e2 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -2111,7 +2111,7 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
> gdb_ctx->s->multiprocess = true;
> }
>
> - pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf), ";multiprocess+");
> + pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf), ";vContSupported+;multiprocess+");
> put_packet(gdb_ctx->s, gdb_ctx->str_buf);
> }
>
> --
> 2.25.0
>
--
Cheers,
Changbin Du
next prev parent reply other threads:[~2020-03-09 10:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-21 0:25 [PATCH v2] gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb Changbin Du
2020-02-21 12:40 ` Luc Michel
2020-03-09 10:43 ` Changbin Du [this message]
2020-03-09 14:48 ` Alex Bennée
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