Re: [PATCH 1/4] pc-bios/s390-ccw: Silence warning from Clang by marking panic() as noreturn

[Thomas Huth]

On 02/05/2021 20.57, Philippe Mathieu-Daudé wrote:
> On 5/2/21 7:48 PM, Thomas Huth wrote:
> > When compiling the s390-ccw bios with Clang, the compiler emits a warning:
> >
> >   pc-bios/s390-ccw/main.c:210:5: warning: variable 'found' is used uninitialized
> >    whenever switch default is taken [-Wsometimes-uninitialized]
> >       default:
> >       ^~~~~~~
> >   pc-bios/s390-ccw/main.c:214:16: note: uninitialized use occurs here
> >       IPL_assert(found, "Boot device not found\n");
> >                  ^~~~~
> >
> > It's a false positive, it only happens because Clang is not smart enough
> > to see that the panic() function in the "default:" case can never return.
> >
> > Anyway, let's explicitely mark panic() with "noreturn" to shut up the
> > warning.
>
> Why not simply initialize the variable instead?

First, it's a false positive. If you only look at the code, someone might 
later wonder whether it's really necessary or not and try to remove it again 
(and since there is no warning with gcc, this patch would also have a good 
chance to get merged, bringing us back to where we are right now).

Second, declaring panic() as noreturn is certainly more sustainable, since 
it might prevent similar situations in other parts of the code in the future.

 Thomas


> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   pc-bios/s390-ccw/s390-ccw.h | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
> > index 6cd92669e9..79db69ff54 100644
> > --- a/pc-bios/s390-ccw/s390-ccw.h
> > +++ b/pc-bios/s390-ccw/s390-ccw.h
> > @@ -89,6 +89,7 @@ bool menu_is_enabled_enum(void);
> >   
> >   #define MAX_BOOT_ENTRIES  31
> >   
> > +__attribute__ ((__noreturn__))
> >   static inline void panic(const char *string)
> >   {
> >       sclp_print(string);