Re: [Qemu-devel] [PATCH] hw/i386/pc: fix possible segment fault for port92_write

[li guang]

在 2013-03-22五的 12:07 +0100，Paolo Bonzini写道：
> Il 22/03/2013 10:12, liguang ha scritto:
> > e.g.
> > $qemu-system-x86_64 -device port92
> > will report segment fault,
> > for port92_write try a un-allocated
> > assignment for a20_out.
> > so check before this assignment.
> > 
> > Signed-off-by: liguang <address@hidden>
> > ---
> >  hw/i386/pc.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index ed7d9ba..a0e8ee0 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -440,7 +440,8 @@ static void port92_write(void *opaque, hwaddr addr, 
> > uint64_t val,
> >  
> >      DPRINTF("port92: write 0x%02x\n", val);
> >      s->outport = val;
> > -    qemu_set_irq(*s->a20_out, (val >> 1) & 1);
> > +    if (s->a20_out)
> > +        qemu_set_irq(*s->a20_out, (val >> 1) & 1);
> >      if (val & 1) {
> >          qemu_system_reset_request();
> >      }
> > 
> 
> Unfortunately, this is a very common problem.  The correct fix is to
> change port92 to use the GPIO mechanism instead.
> 

Sorry, Paolo,
I'm not so familiar with 'GPIO mechanism', 
can you specify more?

Thanks!