linux-kernel - Re: [PATCH 1/4] selftests/cgroup: fix clang build failures for abs() calls

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Date: Fri, 3 May 2024 10:53:52 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>, Tejun Heo <tj@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Waiman Long <longman@...hat.com>,
	Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kselftest@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	llvm@...ts.linux.dev
Subject: Re: [PATCH 1/4] selftests/cgroup: fix clang build failures for abs()
 calls

On Thu, May 02, 2024 at 08:51:02PM -0700, John Hubbard wrote:
> First of all, in order to build with clang at all, one must first apply
> Valentin Obst's build fix for LLVM [1]. Once that is done, then when
> building with clang, via:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> ...clang is pickier than gcc, about which version of abs(3) to call,
> depending on the argument type:
> 
>    int abs(int j);
>    long labs(long j);
>    long long llabs(long long j);
> 
> ...and this is causing both build failures and warnings, when running:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> Fix this by calling labs() in value_close(), because the arguments are
> unambiguously "long" type.
> 
> [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/
> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Reviewed-by: Roman Gushchin <roman.gushchin@...ux.dev>

Thanks!