Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized variable

[Behan Webster]

On 03/22/14 09:29, James Bottomley wrote:
> On Sat, 2014-03-22 at 08:48 -0700, behanw@xxxxxxxxxxxxxxxxxx wrote:
> > From: Behan Webster <behanw@xxxxxxxxxxxxxxxxxx>
> >
> > Fix uninitialized return code in default case in cmpxchg-local.h
> >
> > This patch fixes the code to prevent an uninitialized return value that is detected
> > when compiling with clang. The bug produces numerous warnings when compiling the
> > Linux kernel with clang.
> >
> > Signed-off-by: Behan Webster <behanw@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Mark Charlebois <charlebm@xxxxxxxxx>
> > ---
> >   include/asm-generic/cmpxchg-local.h | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h
> > index d8d4c89..9112111 100644
> > --- a/include/asm-generic/cmpxchg-local.h
> > +++ b/include/asm-generic/cmpxchg-local.h
> > @@ -41,6 +41,7 @@ static inline unsigned long __cmpxchg_local_generic(volatile void *ptr,
> >   		break;
> >   	default:
> >   		wrong_size_cmpxchg(ptr);
> > +		__builtin_unreachable();
> No, that's got to be unreachable() so that it works in all compilers,
> (__builtin_unreachable is a gcc-4 ism).
It is also supported by clang.

> Got to say this still looks wrong.  If wrong_size_cmpxchg() cannot
> return, the function should be annotated as such with __noreturn (like
> panic()) so the unreachable() should be superfluous.
Okay. I can try that instead.

Thanks,

Behan

--
Behan Webster
behanw@xxxxxxxxxxxxxxxxxx

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