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Date: Wed, 17 Jan 2024 10:16:26 +0100
From: Andrew Jones <ajones@ventanamicro.com>
To: Yunhui Cui <cuiyunhui@bytedance.com>
Cc: shuah@kernel.org, paul.walmsley@sifive.com, palmer@dabbelt.com, 
	aou@eecs.berkeley.edu, xiao.w.wang@intel.com, linux-kselftest@vger.kernel.org, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, xuzhipeng.1973@bytedance.com
Subject: Re: [PATCH] RISC-V: selftests: fix cbo.c compilation error
Message-ID: <20240117-274e425c51d0deaeca80857d@orel>
References: <20240117082514.42967-1-cuiyunhui@bytedance.com>
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In-Reply-To: <20240117082514.42967-1-cuiyunhui@bytedance.com>

On Wed, Jan 17, 2024 at 04:25:14PM +0800, Yunhui Cui wrote:
> When compiling with -O0, the following error will occur:
> cbo.c: In function 'cbo_insn':
> cbo.c:43:9: warning: 'asm' operand 1 probably does not match constraints
>    43 |         asm volatile(
>       |         ^~~
> cbo.c:43:9: warning: 'asm' operand 2 probably does not match constraints
> cbo.c:43:9: error: impossible constraint in 'asm'
> 
> Add __attribute__((optimize("O"))) to fix.
> 
> Fixes: a29e2a48afe3 ("RISC-V: selftests: Add CBO tests")
> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
> Suggested-by: Zhipeng Xu <xuzhipeng.1973@bytedance.com>
> ---
>  tools/testing/selftests/riscv/hwprobe/cbo.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/riscv/hwprobe/cbo.c b/tools/testing/selftests/riscv/hwprobe/cbo.c
> index 50a2cc8aef38..ff1d8e843d70 100644
> --- a/tools/testing/selftests/riscv/hwprobe/cbo.c
> +++ b/tools/testing/selftests/riscv/hwprobe/cbo.c
> @@ -36,7 +36,7 @@ static void sigill_handler(int sig, siginfo_t *info, void *context)
>  	regs[0] += 4;
>  }
>  
> -static void cbo_insn(char *base, int fn)
> +static __always_inline void cbo_insn(char *base, int fn)
>  {
>  	uint32_t insn = MK_CBO(fn);
>  
> @@ -47,10 +47,11 @@ static void cbo_insn(char *base, int fn)
>  	: : "r" (base), "i" (fn), "i" (insn) : "a0", "a1", "memory");
>  }
>  
> -static void cbo_inval(char *base) { cbo_insn(base, 0); }
> -static void cbo_clean(char *base) { cbo_insn(base, 1); }
> -static void cbo_flush(char *base) { cbo_insn(base, 2); }
> -static void cbo_zero(char *base)  { cbo_insn(base, 4); }
> +#define OPTIMIZE __attribute__((optimize("O")))
> +OPTIMIZE static void cbo_inval(char *base) { cbo_insn(base, 0); }
> +OPTIMIZE static void cbo_clean(char *base) { cbo_insn(base, 1); }
> +OPTIMIZE static void cbo_flush(char *base) { cbo_insn(base, 2); }
> +OPTIMIZE static void cbo_zero(char *base)  { cbo_insn(base, 4); }
>  
>  static void test_no_zicbom(void *arg)
>  {
> -- 
> 2.20.1
>

Hi Yunhui,

Thanks for the bug report, but this isn't the right fix. The real problem
is that I didn't ensure operands 1 and 2 match their constraints, just as
the warning you discovered says. To do that, I should have made cbo_insn()
a macro and not used the local variable, i.e. ensure 'fn' and 'insn' are
indeed constants derived from the 0,1,2,4 constants.

I'll send a patch with your reported-by.

Thanks,
drew