From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:49109)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <thuth@redhat.com>) id 1cTjOt-0005yo-P3
	for qemu-devel@nongnu.org; Wed, 18 Jan 2017 01:07:16 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <thuth@redhat.com>) id 1cTjOq-0002Mt-KA
	for qemu-devel@nongnu.org; Wed, 18 Jan 2017 01:07:15 -0500
References: <1484709699-3455-1-git-send-email-skiver.cloud.yzy@gmail.com>
From: Thomas Huth <thuth@redhat.com>
Message-ID: <66ed2121-c207-d2f4-2e05-b6474bfa6a49@redhat.com>
Date: Wed, 18 Jan 2017 07:07:08 +0100
MIME-Version: 1.0
In-Reply-To: <1484709699-3455-1-git-send-email-skiver.cloud.yzy@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH v4 1/2] gdbstub.c: fix GDB connection
 segfault caused by empty machines
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Ziyue Yang <skiver.cloud.yzy@gmail.com>, qemu-devel@nongnu.org, qemu-trivial@nongnu.org
Cc: Fam Zheng <famz@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Ziyue Yang <yzylivezh@hotmail.com>

On 18.01.2017 04:21, Ziyue Yang wrote:
> From: Ziyue Yang <yzylivezh@hotmail.com>
> 
> This patch is to fix the segmentation fault caused by attaching
> GDB to a QEMU instance initialized with "-M none" option.
> 
> The bug can be reproduced by
> 
>> ./qemu-system-x86_64 -M none -nographic -S -s
> 
> and attach a GDB to it by
> 
>> gdb -ex 'target remote :1234
> 
> The segmentation fault was originally caused by trying to read
> the information about CPU when communicating with GDB. However,
> it's impossible for any control flow to exist on an empty machine,
> nor can CPU's be hot plugged to an empty machine later by QOM
> commands. So I think simply disabling GDB connections on empty
> machines makes sense.
> 
> Also some updates from fprintf(stderr, ...) to error_report.

Seems like that last sentence is a left-over from your other patch and
should be removed from this patch description here.

> Signed-off-by: Ziyue Yang <skiver.cloud.yzy@gmail.com>
> ---
>  gdbstub.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index de62d26..426d55e 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -18,6 +18,7 @@
>   */
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
> +#include "qemu/error-report.h"
>  #include "qemu/cutils.h"
>  #include "cpu.h"
>  #ifdef CONFIG_USER_ONLY
> @@ -1731,6 +1732,12 @@ int gdbserver_start(const char *device)
>      CharDriverState *mon_chr;
>      ChardevCommon common = { 0 };
> 
> +    if (!first_cpu) {
> +        error_report("gdbstub: meaningless to attach gdb to a "
> +                     "machine without any CPU.");
> +        return -1;
> +    }
> +
>      if (!device)
>          return -1;
>      if (strcmp(device, "none") != 0) {
> --
> 2.7.4
> 

With the "fprintf" sentence removed:

Reviewed-by: Thomas Huth <thuth@redhat.com>