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Message-ID: <CAKwvOdnX6O0Grth11R8JLoD9bp-BECheucZKHbiHt4=XpQferA@mail.gmail.com>
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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