Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 22 Apr 2024 10:40:32 +0100 | From | Mark Rutland <> | Subject | Re: gcc-8: arm64/kvm/pauth.: Error: unknown architectural extension `pauth' |
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On Mon, Apr 22, 2024 at 11:25:25AM +0200, Arnd Bergmann wrote: > On Mon, Apr 22, 2024, at 11:13, Mark Rutland wrote: > > On Mon, Apr 22, 2024 at 02:04:43PM +0530, Naresh Kamboju wrote: > > Given the minimum supported toolchain comes with an assembler that doesn't > > necessarily support ARMv8.3, I reckon we'll either have to make NV pauth > > support depend upon AS_HAS_ARMV8_3, or manually assemble the PACGA instruction. > > > > I suspect the latter is the better option. > > The .config linked from the report shows > > CONFIG_AS_VERSION=23101 > CONFIG_ARM64_PTR_AUTH_KERNEL=y > CONFIG_AS_HAS_ARMV8_3=y > > So it gets detected as supporting ARMv8.3. Is this the wrong > conditional to check, or does it get misdetected for an unsupported > assembler?
I suspect that means the 'pauth' arch extension was added after armv8.3 support, and the assembler supports `-march=armv8.3-a` but does not support `.arch_extension pauth`. So for this code, it'd be wrong to check for AS_HAS_ARMV8_3, unless we used `.march armv8.3-a`, but even then that'd still mean configurations where we couldn't support this code.
I reckon manually assembing the PACGA is the best thing to do; that sidesteps the need for either `.arch_extension pauth` or `.march armv8.3-a`, and aligns with what we do for CONFIG_ARM64_PTR_AUTH=y generally.
Elsewhere in the kernel where we check for CONFIG_AS_HAS_ARMV8_3, we rely on ARM64_ASM_PREAMBLE containing `.arch armv8.3-a` or a later version that implies the presence of ARMv8.3-A instructions, and so pauth usage elsewhere is fine.
Mark.
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