linux-kernel - Re: linux-next: build warning after merge of the bitmap tree

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Message-ID: <c8c94357-8367-42b9-a817-f4ae3feacdf2@arm.com>
Date: Thu, 10 Jul 2025 09:44:09 +0100
From: Ben Horgan <ben.horgan@....com>
To: Stephen Rothwell <sfr@...b.auug.org.au>, Yury Norov <yury.norov@...il.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of the bitmap tree

Hi Stephen,

On 7/10/25 09:34, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the bitmap tree, today's linux-next build (arm64 defconfig)
> produced this warning:
> 
> arch/arm64/kvm/sys_regs.c: In function 'access_mdcr':
> arch/arm64/kvm/sys_regs.c:2654:17: warning: ignoring return value of 'u64_replace_bits' declared with attribute 'warn_unused_result' [-Wunused-result]
>   2654 |                 u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Introduced by commit
> 
>    f66f9c3d09c1 ("bitfield: Ensure the return values of helper functions are checked")
> 

Sorry to have broken your tree. However, this is a valid warning and 
this misuse of u64_replace_bits() was the motivation for the commit.

The fix can be found here 
https://lore.kernel.org/kvmarm/20250709093808.920284-1-ben.horgan@arm.com/T/#mc9e47859302654d84b4f2b3d9032d2b595d5df49

Thanks,

Ben