Re: [PATCH] arm64: lse: Fix LSE atomics with LLVM

From: Will Deacon <will@kernel.org>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: catalin.marinas@arm.com, will.deacon@arm.com,
	clang-built-linux@googlegroups.com, samitolvanen@google.com,
	amit.kachhap@arm.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: lse: Fix LSE atomics with LLVM
Date: Tue, 18 Feb 2020 16:54:52 +0000	[thread overview]
Message-ID: <20200218165451.GE1133@willie-the-truck> (raw)
In-Reply-To: <20200218164906.35685-1-vincenzo.frascino@arm.com>

[+Sami]

On Tue, Feb 18, 2020 at 04:49:06PM +0000, Vincenzo Frascino wrote:
> The introduction of the commit e0d5896bd356cd broke the compilation of
> the kernel when the selected compiler is clang and it is used in
> combination with "-no-integrated-as".

Curious, but have you tested this change with the integrated assembler as
well?

> This happens because __LSE_PREAMBLE is defined as ".arch armv8-a+lse"
> and this overrides the version of the architecture passed via -march
> command line to the gas compiler.
> 
> The issue was noticed during the development of pauth on arm64 and an
> error example is reported below:
> 
> $ aarch64-none-linux-gnu-as -EL -I ./arch/arm64/include
>                                 -I ./arch/arm64/include/generated
>                                 -I ./include -I ./include
>                                 -I ./arch/arm64/include/uapi
>                                 -I ./arch/arm64/include/generated/uapi
>                                 -I ./include/uapi -I ./include/generated/uapi
>                                 -I ./init -I ./init
>                                 -march=armv8.3-a -o init/do_mounts.o
>                                 /tmp/do_mounts-d7992a.s
> /tmp/do_mounts-d7992a.s: Assembler messages:
> /tmp/do_mounts-d7992a.s:1959: Error: selected processor does not support `autiasp'
> /tmp/do_mounts-d7992a.s:2021: Error: selected processor does not support `paciasp'
> /tmp/do_mounts-d7992a.s:2157: Error: selected processor does not support `autiasp'
> /tmp/do_mounts-d7992a.s:2175: Error: selected processor does not support `paciasp'
> /tmp/do_mounts-d7992a.s:2494: Error: selected processor does not support `autiasp'
> 
> Fix the issue replacing ".arch armv8-a+lse" with ".arch_extension lse" that does
> not override the command line parameter.
> 
> Fixes: e0d5896bd356cd ("arm64: lse: fix LSE atomics with LLVM's integrated assembler")
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Reported-by: Amit Kachhap <Amit.Kachhap@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
>  arch/arm64/include/asm/lse.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/lse.h b/arch/arm64/include/asm/lse.h
> index d429f7701c36..5d10051c3e62 100644
> --- a/arch/arm64/include/asm/lse.h
> +++ b/arch/arm64/include/asm/lse.h
> @@ -6,7 +6,7 @@
>  
>  #ifdef CONFIG_ARM64_LSE_ATOMICS
>  
> -#define __LSE_PREAMBLE	".arch armv8-a+lse\n"
> +#define __LSE_PREAMBLE	".arch_extension lse\n"

I'm ok with this, but Sami assumedly changed this for a reason in
e0d5896bd356cd ("arm64: lse: fix LSE atomics with LLVM's integrated
assembler").

Sami?

Will

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