diff options
| author | Marc Zyngier <marc.zyngier@arm.com> | 2015-06-01 10:47:42 +0100 |
|---|---|---|
| committer | David Brown <david.brown@linaro.org> | 2015-12-03 16:53:50 -0800 |
| commit | 955e2603bf69918b3c1592ce008324192c855647 (patch) | |
| tree | ac8a3918dcd53da8a232a32ac78ccf27c4b87915 | |
| parent | b765d5d626c016e03a3b5d02468210344b194019 (diff) | |
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.h | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index 1c2ec6860252..ec1295139dbc 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -25,7 +25,20 @@ 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" \ @@ -38,9 +51,8 @@ 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 @@ -60,9 +72,8 @@ 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__ */ |