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authorMarc Zyngier <marc.zyngier@arm.com>2015-06-01 10:47:42 +0100
committerDavid Brown <david.brown@linaro.org>2015-12-08 08:37:01 -0800
commit348dc8b434c5f78bab436154e1b54e5441805261 (patch)
tree7a50f9c1d674cd10293d5a83436602ccbd83bec5
parent4739dc10110863af3ccbe7e923b061c04ca5069a (diff)
downloadlinux-linaro-stable-348dc8b434c5f78bab436154e1b54e5441805261.tar.gz
arm64: alternative: Work around .inst assembler bugs
commit eb7c11ee3c5ce6c45ac28a5015a8e60ed458b412 upstream. AArch64 toolchains suffer from the following bug: $ cat blah.S 1: .inst 0x01020304 .if ((. - 1b) != 4) .error "blah" .endif $ aarch64-linux-gnu-gcc -c blah.S blah.S: Assembler messages: blah.S:3: Error: non-constant expression in ".if" statement which precludes the use of msr_s and co as part of alternatives. We workaround this issue by not directly testing the labels themselves, but by moving the current output pointer by a value that should always be zero. If this value is not null, then we will trigger a backward move, which is expclicitely forbidden. This triggers the error we're after: AS arch/arm64/kvm/hyp.o arch/arm64/kvm/hyp.S: Assembler messages: arch/arm64/kvm/hyp.S:1377: Error: attempt to move .org backwards scripts/Makefile.build:294: recipe for target 'arch/arm64/kvm/hyp.o' failed make[1]: *** [arch/arm64/kvm/hyp.o] Error 1 Makefile:946: recipe for target 'arch/arm64/kvm' failed Not pretty, but at least works on the current toolchains. Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: David Brown <david.brown@linaro.org>
-rw-r--r--arch/arm64/include/asm/alternative.h25
1 files changed, 18 insertions, 7 deletions
diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index 265b13ea02ee..c385a0c4057f 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -26,7 +26,20 @@ void free_alternatives_memory(void);
" .byte 662b-661b\n" /* source len */ \
" .byte 664f-663f\n" /* replacement len */
-/* alternative assembly primitive: */
+/*
+ * alternative assembly primitive:
+ *
+ * If any of these .org directive fail, it means that insn1 and insn2
+ * don't have the same length. This used to be written as
+ *
+ * .if ((664b-663b) != (662b-661b))
+ * .error "Alternatives instruction length mismatch"
+ * .endif
+ *
+ * but most assemblers die if insn1 or insn2 have a .inst. This should
+ * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
+ * containing commit 4e4d08cf7399b606 or c1baaddf8861).
+ */
#define ALTERNATIVE(oldinstr, newinstr, feature) \
"661:\n\t" \
oldinstr "\n" \
@@ -39,9 +52,8 @@ void free_alternatives_memory(void);
newinstr "\n" \
"664:\n\t" \
".popsection\n\t" \
- ".if ((664b-663b) != (662b-661b))\n\t" \
- " .error \"Alternatives instruction length mismatch\"\n\t"\
- ".endif\n"
+ ".org . - (664b-663b) + (662b-661b)\n\t" \
+ ".org . - (662b-661b) + (664b-663b)\n"
#else
@@ -61,9 +73,8 @@ void free_alternatives_memory(void);
.pushsection .altinstr_replacement, "ax"
663: \insn2
664: .popsection
- .if ((664b-663b) != (662b-661b))
- .error "Alternatives instruction length mismatch"
- .endif
+ .org . - (664b-663b) + (662b-661b)
+ .org . - (662b-661b) + (664b-663b)
.endm
#endif /* __ASSEMBLY__ */