linux-kernel - Re: [PATCH] arm64: tlb: fix ARM64_TLB_RANGE with LLVM's integrated assembler

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Message-ID: <CAKwvOdncvJbxphoDFdWTeiMnuu4pDie9xCxA-dC=__CK9p1KBw@mail.gmail.com>
Date:   Wed, 5 Aug 2020 12:15:54 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Zhenyu Ye <yezhenyu2@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        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: tlb: fix ARM64_TLB_RANGE with LLVM's integrated assembler

On Wed, Aug 5, 2020 at 11:19 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> Commit 7c78f67e9bd9 ("arm64: enable tlbi range instructions") breaks
> LLVM's integrated assembler, because -Wa,-march is only passed to
> external assemblers and therefore, the new instructions are not enabled
> when IAS is used.
>
> As binutils doesn't support .arch_extension tlb-rmi, this change adds
> .arch armv8.4-a to __TLBI_0 and __TLBI_1 to fix the issue with both LLVM
> IAS and binutils.
>
> Fixes: 7c78f67e9bd9 ("arm64: enable tlbi range instructions")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1106
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

I've filed https://sourceware.org/bugzilla/show_bug.cgi?id=26339 to
discuss more with ARM binutils devs about some of the compat issues
around these assembler directives.

> ---
>  arch/arm64/include/asm/tlbflush.h | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index d493174415db..66c2aab5e9cb 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -16,6 +16,16 @@
>  #include <asm/cputype.h>
>  #include <asm/mmu.h>
>
> +/*
> + * Enable ARMv8.4-TLBI instructions with ARM64_TLB_RANGE. Note that binutils
> + * doesn't support .arch_extension tlb-rmi, so use .arch armv8.4-a instead.
> + */
> +#ifdef CONFIG_ARM64_TLB_RANGE
> +#define __TLBI_PREAMBLE        ".arch armv8.4-a\n"
> +#else
> +#define __TLBI_PREAMBLE
> +#endif
> +
>  /*
>   * Raw TLBI operations.
>   *
> @@ -28,14 +38,16 @@
>   * not. The macros handles invoking the asm with or without the
>   * register argument as appropriate.
>   */
> -#define __TLBI_0(op, arg) asm ("tlbi " #op "\n"                                       \
> +#define __TLBI_0(op, arg) asm (__TLBI_PREAMBLE                                \
> +                              "tlbi " #op "\n"                                \
>                    ALTERNATIVE("nop\n                   nop",                  \
>                                "dsb ish\n               tlbi " #op,            \
>                                ARM64_WORKAROUND_REPEAT_TLBI,                   \
>                                CONFIG_ARM64_WORKAROUND_REPEAT_TLBI)            \
>                             : : )
>
> -#define __TLBI_1(op, arg) asm ("tlbi " #op ", %0\n"                           \
> +#define __TLBI_1(op, arg) asm (__TLBI_PREAMBLE                                \
> +                              "tlbi " #op ", %0\n"                            \
>                    ALTERNATIVE("nop\n                   nop",                  \
>                                "dsb ish\n               tlbi " #op ", %0",     \
>                                ARM64_WORKAROUND_REPEAT_TLBI,                   \
>
> base-commit: 4834ce9d8e074bb7ae197632e0708219b9f389b5
> --
> 2.28.0.163.g6104cc2f0b6-goog
>


-- 
Thanks,
~Nick Desaulniers