linux-kernel - Re: [PATCH] powerpc/bitops: Fix possible undefined behaviour with fls() and fls64()

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Date:   Wed, 25 Nov 2020 22:57:41 +1100 (AEDT)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>, jakub@...hat.com,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        segher@...nel.crashing.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/bitops: Fix possible undefined behaviour with fls() and fls64()

On Thu, 22 Oct 2020 14:05:46 +0000 (UTC), Christophe Leroy wrote:
> fls() and fls64() are using __builtin_ctz() and _builtin_ctzll().
> On powerpc, those builtins trivially use ctlzw and ctlzd power
> instructions.
> 
> Allthough those instructions provide the expected result with
> input argument 0, __builtin_ctz() and __builtin_ctzll() are
> documented as undefined for value 0.
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/bitops: Fix possible undefined behaviour with fls() and fls64()
      https://git.kernel.org/powerpc/c/1891ef21d92c4801ea082ee8ed478e304ddc6749

cheers