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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 18 Oct 2021 12:40:51 -0700
Message-ID: <CAKwvOdm5F1LhgyCtJTYYSQMw47FxxE0m+tOnuUgKXwBHEVxS+g@mail.gmail.com>
Subject: Re: [PATCH] nfp: bpf: Fix bitwise vs. logical OR warning
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Simon Horman <simon.horman@corigine.com>,
        Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>, oss-drivers@corigine.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org, llvm@lists.linux.dev
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On Mon, Oct 18, 2021 at 12:39 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, Oct 18, 2021 at 12:31 PM Nathan Chancellor <nathan@kernel.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@google.com>

Perhaps:

Fixes: 995e101ffa71 ("nfp: bpf: encode extended LM pointer operands")

>
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1479
> > Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> > Signed-off-by: Nathan Chancellor <nathan@kernel.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


-- 
Thanks,
~Nick Desaulniers