Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > On Tue, Dec 10, 2019 at 04:38:54PM +1100, Michael Ellerman wrote: > >> Good question, I'll have a look. >> >> There seems to be confusion about what the type of the bit number is, >> which is leading to sign extension in some cases and not others. > > Shiny. > >> It looks like the type should be unsigned long? > > I'm thinking unsigned makes most sense, I mean, negative bit offsets > should 'work' but that's almost always guaranteed to be an out-of-bound > operation. Yeah I agree. > As to 'long' vs 'int', I'm not sure, 4G bits is a long bitmap. But I > suppose since the bitmap itself is 'unsigned long', we might as well use > 'unsigned long' for the bitnr too. 4G is a lot of bits, but it's not *that* many. eg. If we had a bit per 4K page on a 32T machine that would be 8G bits. So unsigned long seems best. >> Documentation/core-api/atomic_ops.rst: void __clear_bit_unlock(unsigned long nr, unsigned long *addr); >> arch/mips/include/asm/bitops.h:static inline void __clear_bit_unlock(unsigned long nr, volatile unsigned long *addr) >> arch/powerpc/include/asm/bitops.h:static inline void arch___clear_bit_unlock(int nr, volatile unsigned long *addr) >> arch/riscv/include/asm/bitops.h:static inline void __clear_bit_unlock(unsigned long nr, volatile unsigned long *addr) >> arch/s390/include/asm/bitops.h:static inline void arch___clear_bit_unlock(unsigned long nr, >> include/asm-generic/bitops/instrumented-lock.h:static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr) >> include/asm-generic/bitops/lock.h:static inline void __clear_bit_unlock(unsigned int nr, >> >> So I guess step one is to convert our versions to use unsigned long, so >> we're at least not tripping over that difference when comparing the >> assembly. > > Yeah, I'll look at fixing the generic code, bitops/atomic.h and > bitops/non-atomic.h don't even agree on the type of bitnr. Thanks. cheers
