linux-kernel - Re: [PATCH] arm64: Fix multiple 'asm-operand-widths' warnings

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Date:   Tue, 2 May 2017 11:27:18 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>
Subject: Re: [PATCH] arm64: Fix multiple 'asm-operand-widths' warnings

Hi Matthias,

On Mon, May 01, 2017 at 02:26:22PM -0700, Matthias Kaehlcke wrote:
> clang raises 'asm-operand-widths' warnings in inline assembly code when
> the size of an operand is < 64 bits and the operand width is unspecified.
> Most warnings are raised in macros, i.e. the datatype of the operand may
> vary. Forcing the use of an x register through the 'x' operand modifier
> would silence the warning however it involves the risk that for operands
> < 64 bits 'unused' bits may be assigned to 64-bit values (more details at
> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/503816.html).
> Instead we cast the operand to 64 bits, which also forces the use of a
> x register, but without the unexpected behavior.
> 
> In gic_write_bpr1() use write_sysreg_s() to write the register. This
> aligns the functions with others in this header and fixes an
> 'asm-operand-widths' warning.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
>  arch/arm64/include/asm/arch_gicv3.h  | 2 +-
>  arch/arm64/include/asm/barrier.h     | 2 +-
>  arch/arm64/include/asm/uaccess.h     | 2 +-
>  arch/arm64/kernel/armv8_deprecated.c | 2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)

Thanks for putting this together.

Just to check, are these the only instances that you see clang warning
about?

There are a number of other cases where we can see similar problems
(e.g. passing a u8 value to an smp_store_release() on a u32 variable),
so we need to fix more than the clang warnings.

I'm currently attempting a systematic audit of our inline asm to correct
all instances, looking at:

	git grep -e asm \
	--and --not -e 'include' \
	--and --not -e 'asmlinkage' \
	-- arch/arm64

I hope to have patches shortly, and will keep you informed.

Thanks,
Mark.

> 
> diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
> index f37e3a21f6e7..9092d612d8c2 100644
> --- a/arch/arm64/include/asm/arch_gicv3.h
> +++ b/arch/arm64/include/asm/arch_gicv3.h
> @@ -166,7 +166,7 @@ static inline void gic_write_sre(u32 val)
>  
>  static inline void gic_write_bpr1(u32 val)
>  {
> -	asm volatile("msr_s " __stringify(ICC_BPR1_EL1) ", %0" : : "r" (val));
> +	write_sysreg_s(val, ICC_BPR1_EL1);
>  }
>  
>  #define gic_read_typer(c)		readq_relaxed(c)
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index 4e0497f581a0..1248401b07ab 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -60,7 +60,7 @@ do {									\
>  		break;							\
>  	case 8:								\
>  		asm volatile ("stlr %1, %0"				\
> -				: "=Q" (*p) : "r" (v) : "memory");	\
> +			      : "=Q" (*p) : "r" ((__u64)v) : "memory");	\
>  		break;							\
>  	}								\
>  } while (0)
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 5308d696311b..7db143689694 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -302,7 +302,7 @@ do {									\
>  	"	.previous\n"						\
>  	_ASM_EXTABLE(1b, 3b)						\
>  	: "+r" (err)							\
> -	: "r" (x), "r" (addr), "i" (-EFAULT))
> +	: "r" ((__u64)x), "r" (addr), "i" (-EFAULT))
>  
>  #define __put_user_err(x, ptr, err)					\
>  do {									\
> diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
> index 657977e77ec8..79b9fef48b14 100644
> --- a/arch/arm64/kernel/armv8_deprecated.c
> +++ b/arch/arm64/kernel/armv8_deprecated.c
> @@ -306,7 +306,7 @@ do {								\
>  	_ASM_EXTABLE(0b, 4b)					\
>  	_ASM_EXTABLE(1b, 4b)					\
>  	: "=&r" (res), "+r" (data), "=&r" (temp), "=&r" (temp2)	\
> -	: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT),		\
> +	: "r" ((__u64)addr), "i" (-EAGAIN), "i" (-EFAULT),	\
>  	  "i" (__SWP_LL_SC_LOOPS)				\
>  	: "memory");						\
>  	uaccess_disable();					\
> -- 
> 2.13.0.rc0.306.g87b477812d-goog
>