Messages in this thread Patch in this message | | | Date | Fri, 20 Jun 2008 13:05:30 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction |
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Ingo Molnar wrote: > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > > >> On Fri, 20 Jun 2008, Jeremy Fitzhardinge wrote: >> >>> Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)": >>> >> Yeah, I was a bit worried about that. Gcc sometimes does insane >> things. >> >> We literally just tested that the asm should only _ever_ be generated >> with a constant value, but if some gcc dead-code removal thing doesn't >> work, it will then screw up and try to generate the asm even for a >> non-constant thing. >> >> The fairly trivial fix is probably to just change the "i" to "ir", >> safe in the knowledge that any _sane_ case will never use the "r" >> possibility. I suspect even your insane case will end up then killing >> the bad choice later. >> > > okay - Jeremy, could you try the fix below? (or tip/master, i just > pushed this out) > >
Hm. On 32-bit I get these, but they're warnings. On 64-bit they're errors.
{standard input}: Assembler messages: {standard input}:1609: Warning: using `%dl' instead of `%edx' due to `b' suffix
vs
{standard input}: Assembler messages: {standard input}:20511: Error: Incorrect register `%eax' used with `b' suffix
> (i dont use gcc 3.x myself to build the kernel, had way too many > miscompilations in randconfig tests in the past.) >
I do it mainly to pick up these kinds of problems.
> Ingo > > --------------> > commit b68b80b8ab39c42707dc126c41e87d46edc97c27 > Author: Ingo Molnar <mingo@elte.hu> > Date: Fri Jun 20 21:50:20 2008 +0200 > > x86, bitops: make constant-bit set/clear_bit ops faster, gcc workaround > > Jeremy Fitzhardinge reported this compiler bug: > > Suggestion from Linus: add "r" to the input constraint of the > set_bit()/clear_bit()'s constant 'nr' branch: > > Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)": > > CC init/main.o > include2/asm/bitops.h: In function `start_kernel': > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: warning: asm operand 1 probably doesn't match constraints > include2/asm/bitops.h:59: error: impossible constraint in `asm' > include2/asm/bitops.h:59: error: impossible constraint in `asm' > include2/asm/bitops.h:59: error: impossible constraint in `asm' > > Reported-by: Jeremy Fitzhardinge <jeremy@goop.org> > Signed-off-by: Ingo Molnar <mingo@elte.hu> > > diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h > index 6c50548..4575de4 100644 > --- a/include/asm-x86/bitops.h > +++ b/include/asm-x86/bitops.h > @@ -58,7 +58,7 @@ static inline void set_bit(unsigned int nr, volatile unsigned long *addr) > if (IS_IMMEDIATE(nr)) { > asm volatile(LOCK_PREFIX "orb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "i" (CONST_MASK(nr)) > + : "ir" (CONST_MASK(nr)) > : "memory"); > } else { > asm volatile(LOCK_PREFIX "bts %1,%0" > @@ -95,7 +95,7 @@ static inline void clear_bit(int nr, volatile unsigned long *addr) > if (IS_IMMEDIATE(nr)) { > asm volatile(LOCK_PREFIX "andb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "i" (~CONST_MASK(nr))); > + : "ir" (~CONST_MASK(nr))); > } else { > asm volatile(LOCK_PREFIX "btr %1,%0" > : BITOP_ADDR(addr) >
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