Re: [PATCH 9/9] hw/timer/renesas_tmr: silence the compiler warnings

[Peter Maydell]

On Wed, 28 Oct 2020 at 15:07, Thomas Huth <thuth@redhat.com> wrote:
>
> On 28/10/2020 10.59, Philippe Mathieu-Daudé wrote:
> > On 10/28/20 5:18 AM, Chen Qun wrote:
> >> When using -Wimplicit-fallthrough in our CFLAGS, the compiler showed 
> >> warning:
> >> ../hw/timer/renesas_tmr.c: In function ‘tmr_read’:
> >> ../hw/timer/renesas_tmr.c:221:19: warning: this statement may fall through 
> >> [-Wimplicit-fallthrough=]
> >>   221 |         } else if (ch == 0) {i
> >>       |                   ^
> >> ../hw/timer/renesas_tmr.c:224:5: note: here
> >>   224 |     case A_TCORB:
> >>       |     ^~~~
> >>
> >> 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>
> >> ---
> >> Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
> >> Cc: Magnus Damm <magnus.damm@gmail.com>
> >> ---
> >>  hw/timer/renesas_tmr.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/hw/timer/renesas_tmr.c b/hw/timer/renesas_tmr.c
> >> index 446f2eacdd..e03a8155b2 100644
> >> --- a/hw/timer/renesas_tmr.c
> >> +++ b/hw/timer/renesas_tmr.c
> >> @@ -221,6 +221,7 @@ static uint64_t tmr_read(void *opaque, hwaddr addr, 
> >> unsigned size)
> >>          } else if (ch == 0) {
> >>              return concat_reg(tmr->tcora);
> >>          }
> >> +        /* fall through */
> >>      case A_TCORB:
> >>          if (size == 1) {
> >>              return tmr->tcorb[ch];
> >>
> >
> > You fixed A_TCORA but not A_TCORB...
>
> A_TCORB cannot fall through, since it always does a "return" in both
> branches of the if-statement.
>
> However, it also looks really odd that A_TCORA falls through to A_TCORB here
> and return that register value instead. Is this really intended? Yoshinori,
> could you please double-check whether this is a bug here, or intended?

See the discussion in this thread:
https://lore.kernel.org/qemu-devel/CAFEAcA8c2dywr=Zxz1ExAV-48JwFU5vbBDDfA=_KE98XamnXiA@mail.gmail.com/
from when Coverity spotting the fall-through.

I think this cleanup patch from Yoshinori deals with the fall-through
stuff by cleaning up that area of the timer device:
https://lore.kernel.org/qemu-devel/20200711154242.41222-1-ysato@users.sourceforge.jp/
It just needs somebody to code-review it :-)

thanks
-- PMM