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SubjectRe: [PATCH] arm64: fix clang warning about TRAMP_VALIAS
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Hi Arnd,

On 3/16/22 6:38 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The newly introduced TRAMP_VALIAS definition causes a build warning
> with clang-14:
>
> arch/arm64/include/asm/vectors.h:66:31: error: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Werror,-Wnull-pointer-arithmetic]
> return (char *)TRAMP_VALIAS + SZ_2K * slot;

It is? Good to know!
(clang 11 doesn't seem to be so fussy)

Just for some more background:
TRAMP_VALIAS existed before, but it wasn't defined if KPTI is disabled at compile time, you can't
do that without CONFIG_EXPERT.
I thought these dummy definitions would be cleaner than #ifdef'ing the code.


> Change the addition to something clang does not complain about.

Acked-by: James Morse <james.morse@arm.com>


Thanks!

James



> I see this warning on 5.17-rc8, but did not test it on linux-next,
> which may already have a fix.
>
> diff --git a/arch/arm64/include/asm/vectors.h b/arch/arm64/include/asm/vectors.h
> index f64613a96d53..bc9a2145f419 100644
> --- a/arch/arm64/include/asm/vectors.h
> +++ b/arch/arm64/include/asm/vectors.h
> @@ -56,14 +56,14 @@ enum arm64_bp_harden_el1_vectors {
> DECLARE_PER_CPU_READ_MOSTLY(const char *, this_cpu_vector);
>
> #ifndef CONFIG_UNMAP_KERNEL_AT_EL0
> -#define TRAMP_VALIAS 0
> +#define TRAMP_VALIAS 0ul
> #endif
>
> static inline const char *
> arm64_get_bp_hardening_vector(enum arm64_bp_harden_el1_vectors slot)
> {
> if (arm64_kernel_unmapped_at_el0())
> - return (char *)TRAMP_VALIAS + SZ_2K * slot;
> + return (char *)(TRAMP_VALIAS + SZ_2K * slot);
>
> WARN_ON_ONCE(slot == EL1_VECTOR_KPTI);
>
>

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