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From:   Heiko Stuebner <heiko@sntech.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Jason Baron <jbaron@akamai.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-riscv@lists.infradead.org
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, Samuel Holland <samuel@sholland.org>,
        Andrew Jones <ajones@ventanamicro.com>,
        Jisheng Zhang <jszhang@kernel.org>
Subject: Re: [PATCH v2] riscv: jump_label: mark arguments as const to satisfy asm constraints
Date:   Tue, 11 Oct 2022 09:39:14 +0200
Message-ID: <2905332.q0ZmV6gNhb@phil>
In-Reply-To: <20221008145437.491-1-jszhang@kernel.org>
References: <20221008145437.491-1-jszhang@kernel.org>
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Am Samstag, 8. Oktober 2022, 16:54:37 CEST schrieb Jisheng Zhang:
> Samuel reported that the static branch usage in cpu_relax() breaks
> building with CONFIG_CC_OPTIMIZE_FOR_SIZE:
> 
> In file included from <command-line>:
> ./arch/riscv/include/asm/jump_label.h: In function 'cpu_relax':
> ././include/linux/compiler_types.h:285:33: warning: 'asm' operand 0
> probably does not match constraints
>   285 | #define asm_volatile_goto(x...) asm goto(x)
>       |                                 ^~~
> ./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
> 'asm_volatile_goto'
>    41 |         asm_volatile_goto(
>       |         ^~~~~~~~~~~~~~~~~
> ././include/linux/compiler_types.h:285:33: error: impossible constraint
> in 'asm'
>   285 | #define asm_volatile_goto(x...) asm goto(x)
>       |                                 ^~~
> ./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro
> 'asm_volatile_goto'
>    41 |         asm_volatile_goto(
>       |         ^~~~~~~~~~~~~~~~~
> make[1]: *** [scripts/Makefile.build:249:
> arch/riscv/kernel/vdso/vgettimeofday.o] Error 1
> make: *** [arch/riscv/Makefile:128: vdso_prepare] Error 2
> 
> Maybe "-Os" prevents GCC from detecting that the key/branch arguments
> can be treated as constants and used as immediate operands. Inspired
> by x86's commit 864b435514b2("x86/jump_label: Mark arguments as const to
> satisfy asm constraints"), and as pointed out by Steven: "The "i"
> constraint needs to be a constant.", let's do similar modifications to
> riscv.
> 
> Tested by CC_OPTIMIZE_FOR_SIZE + gcc and CC_OPTIMIZE_FOR_SIZE + clang.
> 
> Link: https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/
> Link: https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/
> Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support")
> Reported-by: Samuel Holland <samuel@sholland.org>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

I ran into the same build-issue when enabling CC_OPTIMIZE_FOR_SIZE
and this patch fixes it, so

Tested-by: Heiko Stuebner <heiko@sntech.de>