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Date:   Sat, 4 Jan 2020 08:16:58 +0100 (CET)
From:   Julia Lawall <julia.lawall@inria.fr>
To:     Wen Yang <wenyang@linux.alibaba.com>
cc:     Gilles Muller <Gilles.Muller@lip6.fr>,
        Nicolas Palix <nicolas.palix@imag.fr>,
        Michal Marek <michal.lkml@markovi.net>,
        Matthias Maennich <maennich@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Thomas Gleixner <tglx@linutronix.de>, cocci@systeme.lip6.fr,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] coccinelle: semantic patch to check for inappropriate
 do_div() calls
In-Reply-To: <20200104064448.24314-1-wenyang@linux.alibaba.com>
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References: <20200104064448.24314-1-wenyang@linux.alibaba.com>
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--- Please note the new email address ---


On Sat, 4 Jan 2020, Wen Yang wrote:

> do_div() does a 64-by-32 division.
> When the divisor is unsigned long, u64, or s64,
> do_div() truncates it to 32 bits, this means it
> can test non-zero and be truncated to zero for division.

Would it be worth having a specific warning message for the long/unsigned
long case?  If the target architecture has 32 bit longs then the warning
can be immediately ignored.

julia


> This semantic patch is inspired by Mateusz Guzik's patch:
> commit b0ab99e7736a ("sched: Fix possible divide by zero in avg_atom() calculation")
>
> Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
> Cc: Julia Lawall <Julia.Lawall@lip6.fr>
> Cc: Gilles Muller <Gilles.Muller@lip6.fr>
> Cc: Nicolas Palix <nicolas.palix@imag.fr>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: Matthias Maennich <maennich@google.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: cocci@systeme.lip6.fr
> Cc: linux-kernel@vger.kernel.org
> ---
>  scripts/coccinelle/misc/do_div.cocci | 66 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 66 insertions(+)
>  create mode 100644 scripts/coccinelle/misc/do_div.cocci
>
> diff --git a/scripts/coccinelle/misc/do_div.cocci b/scripts/coccinelle/misc/do_div.cocci
> new file mode 100644
> index 0000000..f1b72d1
> --- /dev/null
> +++ b/scripts/coccinelle/misc/do_div.cocci
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/// do_div() does a 64-by-32 division.
> +/// When the divisor is unsigned long, u64, or s64,
> +/// do_div() truncates it to 32 bits, this means it
> +/// can test non-zero and be truncated to zero for division.
> +///
> +//# This makes an effort to find those inappropriate do_div () calls.
> +//
> +// Confidence: Moderate
> +// Copyright: (C) 2020 Wen Yang, Alibaba.
> +// Comments:
> +// Options: --no-includes --include-headers
> +
> +virtual context
> +virtual org
> +virtual report
> +
> +@depends on context@
> +expression f;
> +long l;
> +unsigned long ul;
> +u64 ul64;
> +s64 sl64;
> +
> +@@
> +(
> +* do_div(f, l);
> +|
> +* do_div(f, ul);
> +|
> +* do_div(f, ul64);
> +|
> +* do_div(f, sl64);
> +)
> +
> +@r depends on (org || report)@
> +expression f;
> +long l;
> +unsigned long ul;
> +position p;
> +u64 ul64;
> +s64 sl64;
> +@@
> +(
> +do_div@p(f, l);
> +|
> +do_div@p(f, ul);
> +|
> +do_div@p(f, ul64);
> +|
> +do_div@p(f, sl64);
> +)
> +
> +@script:python depends on org@
> +p << r.p;
> +@@
> +
> +msg="WARNING: WARNING: do_div() does a 64-by-32 division, which may truncation the divisor to 32-bit"
> +coccilib.org.print_todo(p[0], msg)
> +
> +@script:python depends on report@
> +p << r.p;
> +@@
> +
> +msg="WARNING: WARNING: do_div() does a 64-by-32 division, which may truncation the divisor to 32-bit"
> +coccilib.report.print_report(p[0], msg)
> --
> 1.8.3.1
>
>