Re: [Qemu-devel] [PATCH v4 1/2] gdbstub.c: fix GDB connection segfault caused by empty machines

[Thomas Huth <thuth@redhat.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>