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

From: Ben Horgan <[email-masked]>
Date: Thu, 10 Jul 2025 09:44:09 +0100

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/[email-masked]/T/#mc9e47859302654d84b4f2b3d9032d2b595d5df49

Thanks,

Ben