On Tue, Sep 03, 2013 at 03:03:39PM +0100, Markos Chandras wrote:
> >Was this triggered by CONFIG_BUG=n?
> >
> > Ralf
> >
>
> Hi Ralf,
>
> Yes it was triggered by CONFIG_BUG=n
So here's a small test case to demonstrate the issue:
/*
* Definition of BUG taken from asm-generic/bug.h for the CONFIG_BUG=n case
*/
#define BUG() do {} while(0)
int foo(int arg)
{
int res;
if (arg == 1)
res = 23;
else if (arg -= 2)
res = 42;
else
BUG();
return res;
}
[ralf@h7 linux-mips]$ gcc -O2 -Wall -c bug.c
bug.c: In function ‘foo’:
bug.c:17:2: warning: ‘res’ may be used uninitialized in this function [-Wmaybe-uninitialized]
return res;
^
It's fairly obvious to see what's happening here - GCC doesn't know that
the else case can not be reached, thus razorsharply concludes that res
may be used uninitialized.
I think the definition of BUG should be changed to something like
#define BUG() unreachable()
This has the disadvantage of of expanding into a while (1) loop for older
compilers - but that's only for older compilers, relativly minor in
bloat and last I checked BUG() wasn't performance critical ;-)
Ralf
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
include/asm-generic/bug.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 7d10f96..6f78771 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -108,7 +108,7 @@ extern void warn_slowpath_null(const char *file, const int line);
#else /* !CONFIG_BUG */
#ifndef HAVE_ARCH_BUG
-#define BUG() do {} while(0)
+#define BUG() unreachable()
#endif
#ifndef HAVE_ARCH_BUG_ON
