Hi Nathan,
On Tue, Apr 13, 2021 at 5:09 PM Nathan Chancellor nathan@kernel.org wrote:
After commit 2decad92f473 ("arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is set atomically"), LLVM's integrated assembler fails to build entry.S:
<instantiation>:5:7: error: expected assembly-time absolute expression .org . - (664b-663b) + (662b-661b) ^ <instantiation>:6:7: error: expected assembly-time absolute expression .org . - (662b-661b) + (664b-663b) ^
The root cause is LLVM's assembler has a one-pass design, meaning it cannot figure out these instruction lengths when the .org directive is outside of the subsection that they are in, which was changed by the .arch_extension directive added in the above commit.
Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move length validation inside the subsection") to the alternative_endif macro, shuffling the .org directives so that the length validation happen will always happen in the same subsections. alternative_insn has not shown any issue yet but it appears that it could have the same issue in the future so just preemptively change it.
Cc: stable@vger.kernel.org Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences") Link: https://github.com/ClangBuiltLinux/linux/issues/1347 Signed-off-by: Nathan Chancellor nathan@kernel.org
Apologies if my explanation or terminology is off, I am only now getting more familiar with assembly.
arch/arm64/include/asm/alternative-macros.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h index 5df500dcc627..8a078fc662ac 100644 --- a/arch/arm64/include/asm/alternative-macros.h +++ b/arch/arm64/include/asm/alternative-macros.h @@ -97,9 +97,9 @@ .popsection .subsection 1 663: \insn2 -664: .previous
.org . - (664b-663b) + (662b-661b)+664: .org . - (664b-663b) + (662b-661b) .org . - (662b-661b) + (664b-663b)
.previous .endif.endm
@@ -169,11 +169,11 @@ */ .macro alternative_endif 664:
.org . - (664b-663b) + (662b-661b).org . - (662b-661b) + (664b-663b) .if .Lasm_alt_mode==0 .previous .endif
.org . - (664b-663b) + (662b-661b).org . - (662b-661b) + (664b-663b).endm
/*
Thank you for fixing these!
The patch looks correct to me, next-20210413 builds with LLVM_IAS=1 after I applied it, and defconfig built with both Clang and gcc boots normally. Please feel free to add:
Reviewed-by: Sami Tolvanen samitolvanen@google.com Tested-by: Sami Tolvanen samitolvanen@google.com
Sami