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Rusty Russell 7ef88ad561 BUILD_BUG_ON: make it handle more cases 
BUILD_BUG_ON used to use the optimizer to do code elimination or fail
at link time; it was changed to first the size of a negative array (a
nicer compile time error), then (in
8c87df457c) to a bitfield.

This forced us to change some non-constant cases to MAYBE_BUILD_BUG_ON();
as Jan points out in that commit, it didn't work as intended anyway.

bitfields: needs a literal constant at parse time, and can't be put under
	"if (__builtin_constant_p(x))" for example.
negative array: can handle anything, but if the compiler can't tell it's
	a constant, silently has no effect.
link time: breaks link if the compiler can't determine the value, but the
	linker output is not usually as informative as a compiler error.

If we use the negative-array-size method *and* the link time trick,
we get the ability to use BUILD_BUG_ON() under __builtin_constant_p()
branches, and maximal ability for the compiler to detect errors at
build time.

We also document it thoroughly.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jan Beulich <JBeulich@novell.com>
Acked-by: Hollis Blanchard <hollisb@us.ibm.com>
 		2011-01-24 14:45:10 +10:30
..
acpi Merge branch 'acpica' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6 2011-01-20 16:28:34 -08:00
asm-generic fix non-x86 build failure in pmdp_get_and_clear 2011-01-16 15:05:44 -08:00
crypto crypto: padlock - Move padlock.h into include/crypto 2011-01-07 14:52:00 +11:00
drm Revert "drm: Update fbdev fb_fix_screeninfo" 2011-01-14 16:10:28 -08:00
keys keys: add new key-type encrypted 2010-11-29 08:55:29 +11:00
linux BUILD_BUG_ON: make it handle more cases 2011-01-24 14:45:10 +10:30
math-emu
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media [media] v4l: Include linux/videodev2.h in media/v4l2-ctrls.h 2011-01-19 11:52:09 -02:00
mtd
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net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6 2011-01-19 20:25:45 -08:00
pcmcia
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rdma RDMA: Update workqueue usage 2011-01-16 21:16:31 -08:00
rxrpc
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scsi Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
sound ALSA: constify functions in ac97 2011-01-14 19:14:47 +01:00
target [SCSI] target: Add LIO target core v4.0.0-rc6 2011-01-14 10:12:29 -06:00
trace Merge branches 'core-fixes-for-linus', 'x86-fixes-for-linus', 'timers-fixes-for-linus' and 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-01-15 12:45:00 -08:00
video Merge branch 'fbdev/udlfb' 2011-01-06 18:10:09 +09:00
xen Merge branch 'stable/gntdev' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen 2011-01-13 18:46:48 -08:00
Kbuild
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