[PATCH 5.11 064/122] arm64: alternatives: Move length validation in alternative_{insn, endif}

Greg Kroah-Hartman
2021-04-19T13:13:15Z

From: Nathan Chancellor <nathan@kernel.org>

commit 22315a2296f4c251fa92aec45fbbae37e9301b6c upstream.

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.

Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences")
Cc: <stable@vger.kernel.org> # 5.8.x
Link: https://github.com/ClangBuiltLinux/linux/issues/1347
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20210414000803.662534-1-nathan@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/alternative-macros.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- 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

/*