Re: [PATCH] coccinelle: semantic patch to check for inappropriate do_div() calls

[Julia Lawall]

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.
> 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@xxxxxxxxxxxxxxxxx>
> Cc: Julia Lawall <Julia.Lawall@xxxxxxx>
> Cc: Gilles Muller <Gilles.Muller@xxxxxxx>
> Cc: Nicolas Palix <nicolas.palix@xxxxxxx>
> Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
> Cc: Matthias Maennich <maennich@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: cocci@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  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)

A few small issues: You have WARNING: twice in each case, and truncation
should be truncate.

Is there any generic strategy for fixing these issues?

julia