Will: This is a split out version of previous patch, as requested. I have retained a patch at the send of the series to nix alternative_insn but there's no need to take this one for 4.3. Likewise I've fully split out all the switch-over patches so you can just drop them if they bring any merge trouble.
The existing alternative_insn macro has some limitations that make it hard to work with. In particular 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.
This patchset introduces new macros that allow instructions to be presented to the assembler as normal and overcomes these limitations, together with patches to switch all existing users to the new macros.
My view is that these if_not/else/endif macros are more readable than the original macro and that alone might be enough to justify them. However below is an concrete example of an alterntive sequence 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.
v2:
* Split big patch out into atomized components (Will Deacon). To show where I would like to go I have retained a patch to remove assembler_insn() from the code base although, based on Will's email I don't anticipate this patch being taken for 4.3.
* Add some comments to make clear the constraints imposed on alternative sequences.
Daniel Thompson (5): arm64: alternative: Provide if/else/endif assembler macros arm64: mm: Adopt new alternative assembler macros arm64: kernel: Adopt new alternative assembler macros arm64: kvm: Adopt new alternative assembler macros arm64: alternative: Remove alternative_insn macro
arch/arm64/include/asm/alternative.h | 40 ++++++++++++++++++++++++++++++------ arch/arm64/kernel/entry.S | 29 ++++++++++++-------------- arch/arm64/kvm/hyp.S | 12 +++++++++-- arch/arm64/mm/cache.S | 7 ++++++- 4 files changed, 63 insertions(+), 25 deletions(-)
-- 2.4.3