On Mon, 17 Jan 2011, Russell King - ARM Linux wrote: > Add additional instructions to our assembly bitops functions to ensure > that they only operate on word-aligned pointers. This will be necessary > when we switch these operations to use the word-based exclusive > operations. > > Signed-off-by: Russell King <[email protected]>
This breaks the Thumb2 kernel build: AS arch/arm/lib/changebit.o arch/arm/lib/changebit.S: Assembler messages: arch/arm/lib/changebit.S:16: Error: Thumb does not support negative register indexing -- `strne r1,[r1,-r1]' 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. > --- > arch/arm/lib/bitops.h | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/arch/arm/lib/bitops.h b/arch/arm/lib/bitops.h > index d422529..910d599 100644 > --- a/arch/arm/lib/bitops.h > +++ b/arch/arm/lib/bitops.h > @@ -1,6 +1,8 @@ > > #if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_CPU_32v6K) > .macro bitop, instr > + tst r1, #3 > + strne r1, [r1, -r1] @ assert word-aligned > mov r2, #1 > and r3, r0, #7 @ Get bit offset > add r1, r1, r0, lsr #3 @ Get byte offset > @@ -14,6 +16,8 @@ > .endm > > .macro testop, instr, store > + tst r1, #3 > + strne r1, [r1, -r1] @ assert word-aligned > and r3, r0, #7 @ Get bit offset > mov r2, #1 > add r1, r1, r0, lsr #3 @ Get byte offset > @@ -32,6 +36,8 @@ > .endm > #else > .macro bitop, instr > + tst r1, #3 > + strne r1, [r1, -r1] @ assert word-aligned > and r2, r0, #7 > mov r3, #1 > mov r3, r3, lsl r2 > @@ -52,6 +58,8 @@ > * to avoid dirtying the data cache. > */ > .macro testop, instr, store > + tst r1, #3 > + strne r1, [r1, -r1] @ assert word-aligned > add r1, r1, r0, lsr #3 > and r3, r0, #7 > mov r0, #1 > -- > 1.6.2.5 > > > _______________________________________________ > linux-arm-kernel mailing list > [email protected] > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
