On Tue, Jan 18, 2011 at 01:00:21AM -0500, Nicolas Pitre wrote: > I also wonder what happens with a misaligned ldrex/strex... Does the > alignment trap get invoked? If so, the assertion could be put there > instead if that's not done already, removing this overhead from bitops > calls. In the pre-ARMv6 case the alignment trap fixup would be applied > as usual since the ldr/str are not special, but the previous code > allowed for misaligned pointer so result would be no worse than before > in that case. Testing appears to indicate those misaligned bitops are > rather nonexistent so far. Well, whether LDREX/STREX always fault for misalignment is well open to debate. The ARM ARM for ARMv7 seems to imply they will always fault for misaligned accesses. For ARMv6, the situation is less clear - the way the manual is arranged, it suggests that they will if SCTLR.U is set. When it's clear, the ARM ARM doesn't specify what the outcome is. I also don't know how our unaligned fixup will behave with an unaligned LDREX/STREX without checking the bit patterns. So... I think that's too many unknowns to rely on it, especially when filesystem data is at stake. Maybe changing it to: ands ip, r1, #3 strneb r1, [ip] instead? -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
