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

[Yang Ziyue <skiver.cloud.yzy@gmail.com>]

2017-01-18 1:27 GMT+08:00 Thomas Huth <thuth@redhat.com>:
>
> On 17.01.2017 16:19, 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.
>
> Yes, this sounds like a proper and easy fix for the problem.
>
> > Signed-off-by: Ziyue Yang <skiver.cloud.yzy@gmail.com>
> > ---
> >  gdbstub.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/gdbstub.c b/gdbstub.c
> > index de62d26..413e817 100644
> > --- a/gdbstub.c
> > +++ b/gdbstub.c
> > @@ -1731,6 +1731,12 @@ int gdbserver_start(const char *device)
> >      CharDriverState *mon_chr;
> >      ChardevCommon common = { 0 };
> >
> > +    if (!first_cpu) {
> > +        fprintf(stderr, "gdbstub: meaningless to attach gdb to a "
> > +                "machine without any CPU.\n");
> > +        return -1;
> > +    }
>
> Could you maybe rather use error_report() instead of fprintf()? I think
> that's the preferred way to print out an error in QEMU nowadays.

Sure. I've sent a v2 version patch fixing that.

>
>
>  Thomas
>