On Fri, 8 Mar 2013 16:15:48 +0300 Vyacheslav Dubeyko <slava@xxxxxxxxxxx> wrote:
> > I don't see that warning. Whatever gcc you're using appears to be
> > mishandling unreachable(). Please provide details?
> >
>
> The warning is reproducible with special kernel configuration (please, see attached configuration file).
# CONFIG_BUG is not set
Erk yes, CONFIG_BUG=n causes a ton of problems. But in the case of
x86, it should still work OK:
#define BUG() \
do { \
asm volatile("ud2"); \
unreachable(); \
} while (0)
But the problem is that the above code is dependent upon both
CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE. If both these are unset then
we get the stupid implementation, from include/asm-generic/bug.h:
#ifndef HAVE_ARCH_BUG
#define BUG() do {} while(0)
#endif
ie: the kernel silently locks up.
I think it would be better if x86 were to provide the "ud2" version of
BUG() when CONFIG_BUG=n, as well as when CONFIG_DEBUG_BUGVERBOSE=n.
That would probably generate less code than the daft
include/asm-generic/bug.h implementation anyway.
As for why you got those warnings: gcc bug, IMO. If the compiler sees
int x;
do { } while (0);
wibbles(x);
then it should have brains to not tell us that x is used-unintialised.
Sigh.
I'm not particularly enthused about fixing CONFIG_BUG=n stuff. It's a
nuisance.
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