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

From: Stephen Rothwell <[email-masked]>
Date: Thu, 10 Jul 2025 22:00:43 +1000

Hi Ben,

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

Well, normally that fix would have been applied (with appropriate ACKs)
in the same tree and before f66f9c3d09c1 (or in a shared branch merged
into this tree and some other tree).

-- 
Cheers,
Stephen Rothwell