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Date: Fri, 22 Mar 2013 12:07:15 +0100
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Subject: Re: [Qemu-devel] [PATCH] hw/i386/pc: fix possible segment fault for
	port92_write
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To: liguang <lig.fnst@cn.fujitsu.com>
Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org

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 <lig.fnst@cn.fujitsu.com>
> ---
>  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.

Paolo