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

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Date:   Thu, 6 Aug 2020 15:17:40 +0800
From:   Zhenyu Ye <yezhenyu2@...wei.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
CC:     Mark Rutland <mark.rutland@....com>, Marc Zyngier <maz@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Kees Cook <keescook@...omium.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] arm64: tlb: fix ARM64_TLB_RANGE with LLVM's integrated
 assembler

Hi,

On 2020/8/6 2:19, Sami Tolvanen 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.
> 

I have looked through the discussion on Github issues. The best way to
solve this problem is try to pass the "-Wa,-march" parameter to clang
even when IAS is enabled, which may need the cooperation of compilation
tool chains :(

Currently, I think we can solve the problem by passing
the '-march=armv8.4-a' when using the integrated assembler, just like:

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 55bc8546d9c7..e5ce184e98c2 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -91,8 +91,12 @@ KBUILD_CFLAGS += $(branch-prot-flags-y)

 ifeq ($(CONFIG_AS_HAS_ARMV8_4), y)
 # make sure to pass the newest target architecture to -march.
+ifneq ($(LLVM),)
+KBUILD_CFLAGS  += -march=armv8.4-a
+else
 KBUILD_CFLAGS  += -Wa,-march=armv8.4-a
 endif
+endif

 ifeq ($(CONFIG_SHADOW_CALL_STACK), y)


No need to worry about that this might generate instructions that are not
supported on older hardware, because the 'TLB range' feature is only
enabled when the hardware support ARMv8.4.

> 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>

Thanks,
Zhenyu