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SubjectRe: [PATCH] arm64: Fix warning in mte_get_random_tag()
On Thu, 11 Feb 2021 at 13:57, Vincenzo Frascino
<vincenzo.frascino@arm.com> wrote:
>
> The simplification of mte_get_random_tag() caused the introduction of the
> warning below:
>
> In file included from arch/arm64/include/asm/kasan.h:9,
> from include/linux/kasan.h:16,
> from mm/kasan/common.c:14:
> mm/kasan/common.c: In function ‘mte_get_random_tag’:
> arch/arm64/include/asm/mte-kasan.h:45:9: warning: ‘addr’ is used
> uninitialized [-Wuninitialized]
> 45 | asm(__MTE_PREAMBLE "irg %0, %0"
> |
>
> Fix the warning initializing the address to NULL.
>
> Note: mte_get_random_tag() returns a tag and it never dereferences the address,
> hence 'addr' can be safely initialized to NULL.
>
> Fixes: c8f8de4c0887 ("arm64: kasan: simplify and inline MTE functions")
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
>
> This patch is based on linux-next/akpm
>
> arch/arm64/include/asm/mte-kasan.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
> index 3d58489228c0..b2850b750726 100644
> --- a/arch/arm64/include/asm/mte-kasan.h
> +++ b/arch/arm64/include/asm/mte-kasan.h
> @@ -40,7 +40,12 @@ static inline u8 mte_get_mem_tag(void *addr)
> /* Generate a random tag. */
> static inline u8 mte_get_random_tag(void)
> {
> - void *addr;
> + /*
> + * mte_get_random_tag() returns a tag and it
> + * never dereferences the address, hence addr
> + * can be safely initialized to NULL.
> + */
> + void *addr = NULL;
>
> asm(__MTE_PREAMBLE "irg %0, %0"
> : "+r" (addr));
> --
> 2.30.0
>

Might it be better to simply change the asm constraint to "=r" ?

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