linux-kernel - Re: [PATCH] ptp: ocp: Avoid operator precedence warning in ptp_ocp_summary

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Message-ID: <20210917042933.d42m5ijbiiqrctxp@bsd-mbp.dhcp.thefacebook.com>
Date:   Thu, 16 Sep 2021 21:29:33 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Richard Cochran <richardcochran@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] ptp: ocp: Avoid operator precedence warning in
 ptp_ocp_summary_show()

On Thu, Sep 16, 2021 at 12:43:51PM -0700, Nathan Chancellor wrote:
> Clang warns twice:
> 
> drivers/ptp/ptp_ocp.c:2065:16: error: operator '?:' has lower precedence
> than '&'; '&' will be evaluated first
> [-Werror,-Wbitwise-conditional-parentheses]
>                            on & map ? " ON" : "OFF", src);
>                            ~~~~~~~~ ^
> drivers/ptp/ptp_ocp.c:2065:16: note: place parentheses around the '&'
> expression to silence this warning
>                            on & map ? " ON" : "OFF", src);
>                                     ^
>                            (       )
> drivers/ptp/ptp_ocp.c:2065:16: note: place parentheses around the '?:'
> expression to evaluate it first
>                            on & map ? " ON" : "OFF", src);
>                                     ^
> 
> It is clearly intentional that the bitwise operation be done before the
> ternary operation so add the parentheses as it suggests to fix the
> warning.

Actually, the correct fix is to change '&' to '&&', so a logical
operation is done instead of an arithmetic operation.  I believe
this will silence the warning from clang.
-- 
Jonathan