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

Nick Desaulniers
2020-08-05T19:18:28Z

On Wed, Aug 5, 2020 at 11:19 AM Sami Tolvanen <samitolvanen@google.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@google.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