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>
1 file changed