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

Catalin Marinas
2020-07-30T17:24:37Z

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@google.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@arm.com>

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

--
Catalin