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From: Nathan Chancellor <natechancellor@gmail.com>
To: Antony Yu <swpenim@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [RESEND,PATCH] ARM: fix __div64_32() error when compiling with clang
Date: Mon, 23 Nov 2020 11:16:02 -0700	[thread overview]
Message-ID: <20201123181602.GA2637357@ubuntu-m3-large-x86> (raw)
In-Reply-To: <20201123073634.6854-1-swpenim@gmail.com>

On Mon, Nov 23, 2020 at 03:36:32PM +0800, Antony Yu wrote:
> __do_div64 clobbers the input register r0 in little endian system.
> According to the inline assembly document, if an input operand is
> modified, it should be tied to a output operand. This patch can
> prevent compilers from reusing r0 register after asm statements.
> 
> Signed-off-by: Antony Yu <swpenim@gmail.com>
> ---
>  arch/arm/include/asm/div64.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
> index 898e9c78a7e7..809efc51e90f 100644
> --- a/arch/arm/include/asm/div64.h
> +++ b/arch/arm/include/asm/div64.h
> @@ -39,9 +39,10 @@ static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
>  	asm(	__asmeq("%0", __xh)
>  		__asmeq("%1", "r2")
>  		__asmeq("%2", "r0")
> -		__asmeq("%3", "r4")
> +		__asmeq("%3", "r0")
> +		__asmeq("%4", "r4")
>  		"bl	__do_div64"
> -		: "=r" (__rem), "=r" (__res)
> +		: "=r" (__rem), "=r" (__res), "=r" (__n)
>  		: "r" (__n), "r" (__base)
>  		: "ip", "lr", "cc");
>  	*n = __res;
> -- 
> 2.23.0
> 

I am not sure that I am qualified to review this (my assembly knowledge
is not the best) but your commit title mentions an error when compiling
with clang. What is the exact error, what configuration generates it,
and what version of clang? We have done fairly decent testing for
32-bit ARM, I would like to know what we are missing.

Cheers,
Nathan

WARNING: multiple messages have this Message-ID (diff)
From: Nathan Chancellor <natechancellor@gmail.com>
To: Antony Yu <swpenim@gmail.com>
Cc: clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RESEND,PATCH] ARM: fix __div64_32() error when compiling with clang
Date: Mon, 23 Nov 2020 11:16:02 -0700	[thread overview]
Message-ID: <20201123181602.GA2637357@ubuntu-m3-large-x86> (raw)
In-Reply-To: <20201123073634.6854-1-swpenim@gmail.com>

On Mon, Nov 23, 2020 at 03:36:32PM +0800, Antony Yu wrote:
> __do_div64 clobbers the input register r0 in little endian system.
> According to the inline assembly document, if an input operand is
> modified, it should be tied to a output operand. This patch can
> prevent compilers from reusing r0 register after asm statements.
> 
> Signed-off-by: Antony Yu <swpenim@gmail.com>
> ---
>  arch/arm/include/asm/div64.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
> index 898e9c78a7e7..809efc51e90f 100644
> --- a/arch/arm/include/asm/div64.h
> +++ b/arch/arm/include/asm/div64.h
> @@ -39,9 +39,10 @@ static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
>  	asm(	__asmeq("%0", __xh)
>  		__asmeq("%1", "r2")
>  		__asmeq("%2", "r0")
> -		__asmeq("%3", "r4")
> +		__asmeq("%3", "r0")
> +		__asmeq("%4", "r4")
>  		"bl	__do_div64"
> -		: "=r" (__rem), "=r" (__res)
> +		: "=r" (__rem), "=r" (__res), "=r" (__n)
>  		: "r" (__n), "r" (__base)
>  		: "ip", "lr", "cc");
>  	*n = __res;
> -- 
> 2.23.0
> 

I am not sure that I am qualified to review this (my assembly knowledge
is not the best) but your commit title mentions an error when compiling
with clang. What is the exact error, what configuration generates it,
and what version of clang? We have done fairly decent testing for
32-bit ARM, I would like to know what we are missing.

Cheers,
Nathan

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-11-23 18:16 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-23  7:36 [RESEND,PATCH] ARM: fix __div64_32() error when compiling with clang Antony Yu
2020-11-23  7:36 ` Antony Yu
2020-11-23 18:16 ` Nathan Chancellor [this message]
2020-11-23 18:16   ` Nathan Chancellor
2020-11-24  7:42   ` Antony Yu
2020-11-24 10:14     ` Antony Yu
2020-11-24 10:14       ` [RESEND, PATCH] " Antony Yu
2020-11-24 21:06       ` [RESEND,PATCH] " Nick Desaulniers
2020-11-24 21:06         ` [RESEND, PATCH] " Nick Desaulniers
2020-11-30  8:20         ` [PATCH v2] " Antony Yu
2020-11-30  8:20           ` Antony Yu
2020-11-24 23:16 ` [RESEND,PATCH] " kernel test robot
2020-11-24 23:16   ` [RESEND, PATCH] " kernel test robot
2020-11-24 23:16   ` [RESEND,PATCH] " kernel test robot
2020-11-30 10:11 ` Ard Biesheuvel
2020-11-30 10:11   ` [RESEND, PATCH] " Ard Biesheuvel
2020-11-30 10:12   ` [RESEND,PATCH] " Ard Biesheuvel
2020-11-30 10:12     ` [RESEND, PATCH] " Ard Biesheuvel
2020-11-30 10:21     ` [RESEND,PATCH] " Russell King - ARM Linux admin
2020-11-30 10:21       ` Russell King - ARM Linux admin
2020-11-30 10:40       ` Ard Biesheuvel
2020-11-30 10:40         ` [RESEND, PATCH] " Ard Biesheuvel
2020-11-30 13:58         ` [RESEND,PATCH] " David Laight
2020-11-30 13:58           ` David Laight
2020-11-30 14:18           ` Russell King - ARM Linux admin
2020-11-30 14:18             ` Russell King - ARM Linux admin
2020-11-30 15:50     ` Nicolas Pitre
2020-11-30 15:50       ` Nicolas Pitre
2020-11-30 17:18       ` Ard Biesheuvel
2020-11-30 17:18         ` [RESEND, PATCH] " Ard Biesheuvel
2020-11-30 17:52         ` [RESEND,PATCH] " Nicolas Pitre
2020-11-30 17:52           ` Nicolas Pitre
2020-11-30 18:08           ` Ard Biesheuvel
2020-11-30 18:08             ` [RESEND, PATCH] " Ard Biesheuvel

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