Messages in this thread | | | Date | Wed, 16 Dec 2009 14:58:49 +0100 | From | Uwe Kleine-König <> | Subject | Re: [PATCH] ARM: Convert BUG() to use unreachable() |
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Hallo,
On Thu, Dec 10, 2009 at 09:55:51AM -0800, David Daney wrote: > Russell King - ARM Linux wrote: >> On Tue, Dec 08, 2009 at 10:55:38AM +0100, Uwe Kleine-König wrote: >>> Use the new unreachable() macro instead of for(;;); >> >> Have you investigated what effect this has on generated code? > > Yes. > > Pre GCC-4.5 the generated code should be identical as 'unreachable()' > just expands to 'for(;;);' in this case. > > Post GCC-4.5 the generated code should be smaller. I don't have a toolchain using gcc 4.5.
What should we do with this patch? I think in theory the patch is OK. And for pre gcc-4.5 it should not make any difference as we have in include/linux/compiler-gcc4.h:
#if __GNUC_MINOR__ >= 5 ... #define unreachable() __builtin_unreachable() #endif
and in include/linux/compiler.h:
#ifndef unreachable # define unreachable() do { } while (1) #endif
So the only impact if that
do { } while (1)
is used instead of
for(;;)
. My toolchain (based on 4.3.2) produces the same object files with and without the patch.
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- 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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