Hi Daniel,
On Fri, Jul 10, 2015 at 02:48:50PM +0100, Daniel Thompson wrote:
> The existing alternative_insn macro has some limitations that make it
> hard to work with. In partiuclar the fact it takes instructions from it
> own macro arguments means it doesn't play very nicely with C pre-processor
> macros because the macro arguments look like a string to the C
> pre-processor. Workarounds are (probably) possible but things start to
> look ugly.
>
> Introduce an alternative set of macros that allows instructions to be
> presented to the assembler as normal and switch everything over to the
> new macros.
>
> Signed-off-by: Daniel Thompson <daniel.thomp...@linaro.org>
> ---
>
> Notes:
> To be honest these if not/else/endif macros are simply more readable
> than the original macro and that might be enough to justify them on
> their own. However below is an example that is needlessly hard to
> write without them because ICC_PMR_EL1 is a C pre-processor macro.
>
> .macro disable_irq, tmp
> mov \tmp, #ICC_PMR_EL1_MASKED
> alternative_if_not ARM64_HAS_SYSREG_GIC_CPUIF
> msr daifset, #2
> alternative_else
> msr_s ICC_PMR_EL1, \tmp
> alternative_endif
> .endm
>
> The new macros have received a fair degree of testing because I have
> based my (not published since March) pseudo-NMI patch set on them.
>
> arch/arm64/include/asm/alternative.h | 18 ++++++++++++------
> arch/arm64/kernel/entry.S | 29 +++++++++++++----------------
> arch/arm64/kvm/hyp.S | 12 ++++++++++--
> arch/arm64/mm/cache.S | 7 ++++++-
> 4 files changed, 41 insertions(+), 25 deletions(-)
After some consideration, I think I prefer your suggestion over what we
currently have in mainline. However, there are a bunch of patches that
are candidates for 4.3 which will conflict horribly with this.
Would you be able to:
(1) Split this up so that you have a patch introducing the new macro,
then a patch converting entry.S and cache.S then a separate one
for kvm/hyp.S?
(2) Keep alternative_insn around for the moment
(3) Once the dust has settled for 4.3, we can see how easy the old
macro is to remove
Sound ok to you?
Cheers,
Will
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