Messages in this thread Patch in this message | | | Date | Wed, 18 Sep 2013 15:45:33 +0200 | From | Ralf Baechle <> | Subject | Re: [PATCH v2] MIPS: ath79: Avoid using unitialized 'reg' variable |
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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@linux-mips.org>
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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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