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

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Message-Id: <20200730153701.3892953-1-samitolvanen@google.com>
Date:   Thu, 30 Jul 2020 08:37:01 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>
Cc:     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,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v2] arm64/alternatives: move length validation inside the subsection

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"
 
 #define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)	\

base-commit: 83bdc7275e6206f560d247be856bceba3e1ed8f2
-- 
2.28.0.163.g6104cc2f0b6-goog