linux-kernel - Re: [PATCH v2] arm64/alternatives: move length validation inside the subsection

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Message-ID: <20200730172430.GC3128@gaia>
Date:   Thu, 30 Jul 2020 18:24:31 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] arm64/alternatives: move length validation inside the
 subsection

On Thu, Jul 30, 2020 at 08:37:01AM -0700, Sami Tolvanen wrote:
> Commit f7b93d42945c ("arm64/alternatives: use subsections for replacement
> sequences") breaks LLVM's integrated assembler, because due to its
> one-pass design, it cannot compute instruction sequence lengths before the
> layout for the subsection has been finalized. This change fixes the build
> by moving the .org directives inside the subsection, so they are processed
> after the subsection layout is known.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1078
> Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences")
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
> v1 -> v2:
> - Added the missing Fixes tag and dropped CC: stable@.
> 
> ---
>  arch/arm64/include/asm/alternative.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
> index 12f0eb56a1cc..619db9b4c9d5 100644
> --- a/arch/arm64/include/asm/alternative.h
> +++ b/arch/arm64/include/asm/alternative.h
> @@ -77,9 +77,9 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
>  	"663:\n\t"							\
>  	newinstr "\n"							\
>  	"664:\n\t"							\
> -	".previous\n\t"							\
>  	".org	. - (664b-663b) + (662b-661b)\n\t"			\
> -	".org	. - (662b-661b) + (664b-663b)\n"			\
> +	".org	. - (662b-661b) + (664b-663b)\n\t"			\
> +	".previous\n"							\
>  	".endif\n"

Acked-by: Catalin Marinas <catalin.marinas@....com>

There are a few instances of the .org test outside the subsection,
though using in .S files. Are those ok?

-- 
Catalin