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Date: Mon, 7 Oct 2019 14:34:26 -0700 From: Nick Desaulniers <ndesaulniers@...gle.com> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, Kees Cook <keescook@...omium.org>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, clang-built-linux <clang-built-linux@...glegroups.com> Subject: Re: [PATCH] arm64: fix alternatives with LLVM's integrated assembler On Mon, Oct 7, 2019 at 2:14 PM 'Sami Tolvanen' via Clang Built Linux <clang-built-linux@...glegroups.com> wrote: > > LLVM's integrated assembler fails with the following error when > building KVM: > > <inline asm>:12:6: error: expected absolute expression > .if kvm_update_va_mask == 0 > ^ > <inline asm>:21:6: error: expected absolute expression > .if kvm_update_va_mask == 0 > ^ > <inline asm>:24:2: error: unrecognized instruction mnemonic > NOT_AN_INSTRUCTION > ^ > LLVM ERROR: Error parsing inline asm > > These errors come from ALTERNATIVE_CB and __ALTERNATIVE_CFG, > which test for the existence of the callback parameter in inline > assembly using the following expression: > > " .if " __stringify(cb) " == 0\n" > > This works with GNU as, but isn't supported by LLVM. This change > splits __ALTERNATIVE_CFG and ALTINSTR_ENTRY into separate macros > to fix the LLVM build. > > Link: https://github.com/ClangBuiltLinux/linux/issues/472 > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com> > --- > arch/arm64/include/asm/alternative.h | 32 ++++++++++++++++++---------- > 1 file changed, 21 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h > index b9f8d787eea9..324e7d5ab37e 100644 > --- a/arch/arm64/include/asm/alternative.h > +++ b/arch/arm64/include/asm/alternative.h > @@ -35,13 +35,16 @@ void apply_alternatives_module(void *start, size_t length); > static inline void apply_alternatives_module(void *start, size_t length) { } > #endif > > -#define ALTINSTR_ENTRY(feature,cb) \ > +#define ALTINSTR_ENTRY(feature) \ > " .word 661b - .\n" /* label */ \ > - " .if " __stringify(cb) " == 0\n" \ > " .word 663f - .\n" /* new instruction */ \ > - " .else\n" \ > + " .hword " __stringify(feature) "\n" /* feature bit */ \ > + " .byte 662b-661b\n" /* source len */ \ > + " .byte 664f-663f\n" /* replacement len */ > + > +#define ALTINSTR_ENTRY_CB(feature, cb) \ > + " .word 661b - .\n" /* label */ \ > " .word " __stringify(cb) "- .\n" /* callback */ \ > - " .endif\n" \ > " .hword " __stringify(feature) "\n" /* feature bit */ \ > " .byte 662b-661b\n" /* source len */ \ > " .byte 664f-663f\n" /* replacement len */ > @@ -62,15 +65,14 @@ static inline void apply_alternatives_module(void *start, size_t length) { } > * > * Alternatives with callbacks do not generate replacement instructions. > */ > -#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled, cb) \ > +#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled) \ > ".if "__stringify(cfg_enabled)" == 1\n" \ > "661:\n\t" \ > oldinstr "\n" \ > "662:\n" \ > ".pushsection .altinstructions,\"a\"\n" \ > - ALTINSTR_ENTRY(feature,cb) \ > + ALTINSTR_ENTRY(feature) \ > ".popsection\n" \ > - " .if " __stringify(cb) " == 0\n" \ > ".pushsection .altinstr_replacement, \"a\"\n" \ > "663:\n\t" \ > newinstr "\n" \ > @@ -78,17 +80,25 @@ static inline void apply_alternatives_module(void *start, size_t length) { } > ".popsection\n\t" \ > ".org . - (664b-663b) + (662b-661b)\n\t" \ > ".org . - (662b-661b) + (664b-663b)\n" \ > - ".else\n\t" \ > + ".endif\n" > + > +#define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb) \ > + ".if "__stringify(cfg_enabled)" == 1\n" \ > + "661:\n\t" \ > + oldinstr "\n" \ > + "662:\n" \ > + ".pushsection .altinstructions,\"a\"\n" \ > + ALTINSTR_ENTRY_CB(feature, cb) \ > + ".popsection\n" \ > "663:\n\t" \ > "664:\n\t" \ > - ".endif\n" \ > ".endif\n" > > #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...) \ > - __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0) > + __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg)) > > #define ALTERNATIVE_CB(oldinstr, cb) \ > - __ALTERNATIVE_CFG(oldinstr, "NOT_AN_INSTRUCTION", ARM64_CB_PATCH, 1, cb) > + __ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb) > #else > > #include <asm/assembler.h> Should the definition of the ALTERNATIVE macro (arch/arm64/include/asm/alternative.h#L295) also be updated in this patch to not pass `1` as the final parameter? Otherwise with this patch and your LSE one (https://lore.kernel.org/lkml/20191007201452.208067-1-samitolvanen@google.com/T/#u) I get one error on linux-next that looks related: $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang -j71 arch/arm64/kvm/ ... arch/arm64/kvm/hyp/entry.S:109:87: error: too many positional arguments alternative_insn nop, .inst (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1 ^ Since __ALTERNATIVE_CFG now takes one less arg, with your patch? -- Thanks, ~Nick Desaulniers
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