RE: [PATCH 7/9] ppc: silence the compiler warnings

[Chenqun (kuhn)]

> -----Original Message-----
> From: David Gibson [mailto:david@gibson.dropbear.id.au]
> Sent: Thursday, October 29, 2020 7:39 AM
> To: Thomas Huth <thuth@redhat.com>
> Cc: Chenqun (kuhn) <kuhn.chenqun@huawei.com>; qemu-trivial@nongnu.org;
> Euler Robot <euler.robot@huawei.com>; qemu-devel@nongnu.org; ganqixin
> <ganqixin@huawei.com>; Zhanghailiang <zhang.zhanghailiang@huawei.com>;
> qemu-ppc@nongnu.org
> Subject: Re: [PATCH 7/9] ppc: silence the compiler warnings
> 
> On Wed, Oct 28, 2020 at 03:42:31PM +0100, Thomas Huth wrote:
> > On 28/10/2020 05.29, David Gibson wrote:
> > > On Wed, Oct 28, 2020 at 12:18:17PM +0800, Chen Qun wrote:
> > >> When using -Wimplicit-fallthrough in our CFLAGS, the compiler showed
> warning:
> > >> hw/ppc/ppc.c: In function ‘ppc6xx_set_irq’:
> > >> hw/ppc/ppc.c:118:16: warning: this statement may fall through
> [-Wimplicit-fallthrough=]
> > >>   118 |             if (level) {
> > >>       |                ^
> > >> hw/ppc/ppc.c:123:9: note: here
> > >>   123 |         case PPC6xx_INPUT_INT:
> > >>       |         ^~~~
> > >>
> > >> Add the corresponding "fall through" comment to fix it.
> > >>
> > >> Reported-by: Euler Robot <euler.robot@huawei.com>
> > >> Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
> > >
> > > Acked-by: David Gibson <david@gibson.dropbear.id.au>
> > >
> > >> ---
> > >> Cc: David Gibson <david@gibson.dropbear.id.au>
> > >> ---
> > >>  hw/ppc/ppc.c | 1 +
> > >>  1 file changed, 1 insertion(+)
> > >>
> > >> diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c index
> > >> 4a11fb1640..f9eb8f21b4 100644
> > >> --- a/hw/ppc/ppc.c
> > >> +++ b/hw/ppc/ppc.c
> > >> @@ -120,6 +120,7 @@ static void ppc6xx_set_irq(void *opaque, int pin,
> int level)
> > >>              } else {
> > >>                  cpu_ppc_tb_stop(env);
> > >>              }
> > >> +            /* fall through */
> > >>          case PPC6xx_INPUT_INT:
> > >>              /* Level sensitive - active high */
> > >>              LOG_IRQ("%s: set the external IRQ state to %d\n",
> > >
> >
> > Is that fall through actually really the right thing to do here? I'd
> > rather expect to see a PPC_INTERRUPT_DECR instead of a
> > PPC_INTERRUPT_EXT in case someone messes with the TBEN pin? So I
> > assume this is likely rather bug and we should a "break" statement here
> instead?
> 
> Oh.. good catch, I think I misread this.  I thought the change was correct,
> because DECRs look somewhat like external interrupts.  But this is TBEN, not
> a DECR interrupt per se.  So, yes, I think this was a bug and it should be a
> break instead.
> 
This bug looks like it's been hidden for years. Thanks for your point.
According to your opinion, I will modify it in the next version.

Thanks,
Chen Qun
> --
> David Gibson                  | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au        | minimalist, thank you.  NOT _the_
> _other_
>                               | _way_ _around_!
> http://www.ozlabs.org/~dgibson