Re: [PATCH-next] arm: fix clang build warning in include/asm/memory.h

From: Nathan Chancellor <nathan@kernel.org>
To: Yipeng Zou <zouyipeng@huawei.com>
Cc: linux@armlinux.org.uk, ndesaulniers@google.com, morbo@google.com,
	justinstitt@google.com, linus.walleij@linaro.org,
	ssantosh@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH-next] arm: fix clang build warning in include/asm/memory.h
Date: Thu, 14 Mar 2024 17:43:52 -0700	[thread overview]
Message-ID: <20240315004352.GA768888@dev-arch.thelio-3990X> (raw)
In-Reply-To: <20240314075409.2797149-1-zouyipeng@huawei.com>

On Thu, Mar 14, 2024 at 03:54:09PM +0800, Yipeng Zou wrote:
> There is a build error has been founded with build in clang-15.0.4:
> 
> ./arch/arm/include/asm/memory.h:358:12: error: result of comparison "phys addr_t’ (aka 'unsigned int’) > 4294967295 is always false [-Werror, -Wtautological-type-limit-compare]
>                              if (addr > (u32)~0)
>                                  ~~~~ ^ ~~~~~~~
> 
> It will be always goes fail without CONFIG_PHYS_ADDR_T_64BIT.
> 
> Directly silence it by Use CONFIG_PHYS_ADDR_T_64BIT.
> 
> Fixes: 981b6714dbd2 ("ARM: provide improved virt_to_idmap() functionality")
> Signed-off-by: Yipeng Zou <zouyipeng@huawei.com>
> ---
>  arch/arm/include/asm/memory.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index ef2aa79ece5a..64ced9eb42ff 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -347,14 +347,18 @@ static inline bool arm_has_idmap_alias(void)
>  	return IS_ENABLED(CONFIG_MMU) && arch_phys_to_idmap_offset != 0;
>  }
>  
> +#ifdef CONFIG_PHYS_ADDR_T_64BIT
>  #define IDMAP_INVALID_ADDR ((u32)~0)
> +#endif
>  
>  static inline unsigned long phys_to_idmap(phys_addr_t addr)
>  {
>  	if (IS_ENABLED(CONFIG_MMU) && arch_phys_to_idmap_offset) {
>  		addr += arch_phys_to_idmap_offset;
> +#ifdef CONFIG_PHYS_ADDR_T_64BIT
>  		if (addr > (u32)~0)
>  			addr = IDMAP_INVALID_ADDR;
> +#endif
>  	}
>  	return addr;
>  }
> -- 
> 2.34.1
> 

Would it be better to avoid the ifdef's here and just use IS_ENABLED()?
I can't see why this would not work for avoiding that warning.

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index ef2aa79ece5a..fbff07bc3b28 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -353,7 +353,7 @@ static inline unsigned long phys_to_idmap(phys_addr_t addr)
 {
 	if (IS_ENABLED(CONFIG_MMU) && arch_phys_to_idmap_offset) {
 		addr += arch_phys_to_idmap_offset;
-		if (addr > (u32)~0)
+		if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT) && addr > (u32)~0)
 			addr = IDMAP_INVALID_ADDR;
 	}
 	return addr;

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