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

From: Behan Webster
Date: Sat Mar 22 2014 - 12:37:51 EST

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,
+ __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.



Behan Webster

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