On Wed, Apr 22, 2020 at 07:00:28PM +0100, Catalin Marinas wrote: > On Wed, Mar 25, 2020 at 11:50:38AM +0000, Mark Brown wrote: > > Since BTI is a mandatory feature of v8.5 there is no BTI arch_extension, > > you can only enable it by moving the base architecture to v8.5. You'd > > need to use .arch and that feels likely to find us sharp edges to run > > into. > For MTE, .arch armv8-a+memtag won't work since this is only available > with armv8.5-a. My preference would be to have the highest arch version > supported by the kernel in the assembler.h file, i.e. ".arch armv8.5-a" > followed by .arch_extension in each .S file, as needed. I think we decided that .arch_extension was too new to be used for things like the crypto stuff where we still support older toolchains? > Forcing .S files to armv8.5 would not cause any problems with > the base armv8.0 that the kernel image support since it shouldn't change > the opcodes gas generates. The .S files would use alternatives anyway > (or simply have code not called). We do loose the checking that the assembler does that nobody used a newer feature by mistake but yeah, shouldn't affect the output. > The inline asm is slightly more problematic, especially with the clang > builtin assembler which goes in a single pass. But we could do something > similar to what we did with the LSE atomics and raising the base of the > inline asm to armv8.5 (or 8.6 etc., whatever we need in the future). FWIW I did something different to this for BTI so I wasn't using the instructions directly so I was going to abandon this series.
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