linux-kernel - Re: [PATCH] nfp: bpf: Fix bitwise vs. logical OR warning

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Date:   Mon, 18 Oct 2021 12:39:30 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Simon Horman <simon.horman@...igine.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, oss-drivers@...igine.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] nfp: bpf: Fix bitwise vs. logical OR warning

On Mon, Oct 18, 2021 at 12:31 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> A new warning in clang points out two places in this driver where
> boolean expressions are being used with a bitwise OR instead of a
> logical one:
>
> drivers/net/ethernet/netronome/nfp/nfp_asm.c:199:20: error: use of bitwise '|' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
>         reg->src_lmextn = swreg_lmextn(lreg) | swreg_lmextn(rreg);
>                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>                                              ||
> drivers/net/ethernet/netronome/nfp/nfp_asm.c:199:20: note: cast one or both operands to int to silence this warning
> drivers/net/ethernet/netronome/nfp/nfp_asm.c:280:20: error: use of bitwise '|' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
>         reg->src_lmextn = swreg_lmextn(lreg) | swreg_lmextn(rreg);
>                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>                                              ||
> drivers/net/ethernet/netronome/nfp/nfp_asm.c:280:20: note: cast one or both operands to int to silence this warning
> 2 errors generated.
>
> The motivation for the warning is that logical operations short circuit
> while bitwise operations do not. In this case, it does not seem like
> short circuiting is harmful so implement the suggested fix of changing
> to a logical operation to fix the warning.

I agree. Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1479
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/net/ethernet/netronome/nfp/nfp_asm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/netronome/nfp/nfp_asm.c b/drivers/net/ethernet/netronome/nfp/nfp_asm.c
> index 2643ea5948f4..154399c5453f 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfp_asm.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfp_asm.c
> @@ -196,7 +196,7 @@ int swreg_to_unrestricted(swreg dst, swreg lreg, swreg rreg,
>         }
>
>         reg->dst_lmextn = swreg_lmextn(dst);
> -       reg->src_lmextn = swreg_lmextn(lreg) | swreg_lmextn(rreg);
> +       reg->src_lmextn = swreg_lmextn(lreg) || swreg_lmextn(rreg);
>
>         return 0;
>  }
> @@ -277,7 +277,7 @@ int swreg_to_restricted(swreg dst, swreg lreg, swreg rreg,
>         }
>
>         reg->dst_lmextn = swreg_lmextn(dst);
> -       reg->src_lmextn = swreg_lmextn(lreg) | swreg_lmextn(rreg);
> +       reg->src_lmextn = swreg_lmextn(lreg) || swreg_lmextn(rreg);
>
>         return 0;
>  }
>
> base-commit: 041c61488236a5a84789083e3d9f0a51139b6edf
> --
> 2.33.1.637.gf443b226ca
>
>


-- 
Thanks,
~Nick Desaulniers