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authorJim Bos <jim876@xs4all.nl>2010-11-15 15:22:37 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-15 16:27:06 -0500
commit22d3243de86bc92d874abb7c5b185d5c47aba323 (patch)
tree9fd3cde28bd00b88c9958b4aaee402f63d34cfd4 /include
parent620751a25964582595c6e7935777af954b24cb96 (diff)
Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
The fix in commit 6b4e81db2552 ("i8k: Tell gcc that *regs gets clobbered") to work around the gcc miscompiling i8k.c to add "+m (*regs)" caused register pressure problems and a build failure. Changing the 'asm' statement to 'asm volatile' instead should prevent that and works around the gcc bug as well, so we can remove the "+m". [ Background on the gcc bug: a memory clobber fails to mark the function the asm resides in as non-pure (aka "__attribute__((const))"), so if the function does nothing else that triggers the non-pure logic, gcc will think that that function has no side effects at all. As a result, callers will be mis-compiled. Adding the "+m" made gcc see that it's not a pure function, and so does "asm volatile". The problem was never really the need to mark "*regs" as changed, since the memory clobber did that part - the problem was just a bug in the gcc "pure" function analysis - Linus ] Signed-off-by: Jim Bos <jim876@xs4all.nl> Acked-by: Jakub Jelinek <jakub@redhat.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Andreas Schwab <schwab@linux-m68k.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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