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Re: [PATCH 2/6] x86/alternatives: adjust _apply_alternatives() to comply to Misra rule 18.2
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- From: Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>
- Date: Wed, 7 Oct 2026 17:46:20 +0000
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- Delivery-date: Wed, 07 Oct 2026 17:46:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHdQFsfe75+NzGtXk64qzkN3mSrm7byhs6A
- Thread-topic: [PATCH 2/6] x86/alternatives: adjust _apply_alternatives() to comply to Misra rule 18.2
On 9/9/26 15:59, Jan Beulich wrote:
> While avoiding casts would be preferable here, the subtraction ends up
> violating "Subtraction between pointers shall only be applied to pointers
> that address elements of the same array". Use long arithmetic instead.
>
> No functional change intended.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/alternative.c
> +++ b/xen/arch/x86/alternative.c
> @@ -342,13 +342,13 @@ static int init_or_livepatch _apply_alte
>
> /* 0xe8/0xe9 are relative branches; fix the offset. */
> if ( a->repl_len >= 5 && (*buf & 0xfe) == 0xe8 )
> - *(int32_t *)(buf + 1) += repl - orig;
> + *(int32_t *)(buf + 1) += (long)repl - (long)orig;
> else if ( IS_ENABLED(CONFIG_RETURN_THUNK) &&
> a->repl_len > 5 && buf[a->repl_len - 5] == 0xe9 &&
> ((long)repl + a->repl_len +
> *(int32_t *)(buf + a->repl_len - 4) ==
> (long)__x86_return_thunk) )
> - *(int32_t *)(buf + a->repl_len - 4) += repl - orig;
> + *(int32_t *)(buf + a->repl_len - 4) += (long)repl - (long)orig;
>
> a->priv = 1;
>
Reviewed-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
BR, Dmytro.
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