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

[Chenqun (kuhn)]

> -----Original Message-----
> From: Peter Maydell [mailto:peter.maydell@linaro.org]
> Sent: Thursday, October 29, 2020 4:15 AM
> To: Thomas Huth <thuth@redhat.com>
> Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>; Chenqun (kuhn)
> <kuhn.chenqun@huawei.com>; QEMU Developers <qemu-devel@nongnu.org>;
> QEMU Trivial <qemu-trivial@nongnu.org>; Yoshinori Sato
> <ysato@users.sourceforge.jp>; Magnus Damm <magnus.damm@gmail.com>;
> Zhanghailiang <zhang.zhanghailiang@huawei.com>; ganqixin
> <ganqixin@huawei.com>; Euler Robot <euler.robot@huawei.com>
> Subject: Re: [PATCH 9/9] hw/timer/renesas_tmr: silence the compiler warnings
> 
> 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-48JwFU5vbBD
> DfA=_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.so
> urceforge.jp/
> It just needs somebody to code-review it :-)

This cleanup patch has been modified more thoroughly, so let's wait for it 
merge :-)

Thanks,
Chen Qun