linux-kernel - Re: [PATCH v2] coccinelle: misc: add flexible

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Message-ID: <c717ff19-73c3-2369-7b61-318b0a9662ab@linux.com>
Date:   Sun, 13 Sep 2020 09:15:04 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH v2] coccinelle: misc: add flexible_array.cocci script

Hi,

On 9/12/20 5:43 PM, Julia Lawall wrote:
> 
> 
> On Mon, 10 Aug 2020, Denis Efremov wrote:
> 
>> Commit 68e4cd17e218 ("docs: deprecated.rst: Add zero-length and one-element
>> arrays") marks one-element and zero-length arrays as deprecated. Kernel
>> code should always use "flexible array members" instead.
>>
>> The script warns about one-element and zero-length arrays in structs.
>>
>> Cc: Kees Cook <keescook@...omium.org>
>> Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
>> Signed-off-by: Denis Efremov <efremov@...ux.com>
>> ---
>> Changes in v2:
>>  - all uapi headers are now filtered-out. Unfortunately, coccinelle
>>    doesn't provide structure names in Location.current_element.
>>    For structures the field is always "something_else". Thus, there is
>>    no easy way to create a list of existing structures in uapi headers
>>    and suppress the warning only for them, but not for the newly added
>>    uapi structures.
>>  - The pattern doesn't require 2+ fields in a structure/union anymore.
>>    Now it also checks single field structures/unions.
>>  - The pattern simplified and now uses disjuction in array elements
>>    (Thanks, Markus)
>>  - Unions are removed from patch mode
>>  - one-element arrays are removed from patch mode. Correct patch may
>>    involve turning the array to a simple field instead of a flexible
>>    array.
>>
>> On the current master branch, the rule generates:
>>  - context: https://gist.github.com/evdenis/e2b4323491f9eff35376372df07f723c
>>  - patch: https://gist.github.com/evdenis/46081da9d68ecefd07edc3769cebcf32
>>
>>  scripts/coccinelle/misc/flexible_array.cocci | 88 ++++++++++++++++++++
>>  1 file changed, 88 insertions(+)
>>  create mode 100644 scripts/coccinelle/misc/flexible_array.cocci
>>
>> diff --git a/scripts/coccinelle/misc/flexible_array.cocci b/scripts/coccinelle/misc/flexible_array.cocci
>> new file mode 100644
>> index 000000000000..bf6dcda1783e
>> --- /dev/null
>> +++ b/scripts/coccinelle/misc/flexible_array.cocci
>> @@ -0,0 +1,88 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +///
>> +/// Zero-length and one-element arrays are deprecated, see
>> +/// Documentation/process/deprecated.rst
>> +/// Flexible-array members should be used instead.
>> +///
>> +//
>> +// Confidence: High
>> +// Copyright: (C) 2020 Denis Efremov ISPRAS.
>> +// Comments:
>> +// Options: --no-includes --include-headers
>> +
>> +virtual context
>> +virtual report
>> +virtual org
>> +virtual patch
>> +
>> +@...tialize:python@
>> +@@
>> +def relevant(positions):
>> +    for p in positions:
>> +        if "uapi" in p.file:
>> +             return False
>> +    return True
>> +
>> +@r depends on !patch@
>> +identifier name, array;
>> +type T;
>> +position p : script:python() { relevant(p) };
>> +@@
>> +
>> +(
>> +  struct name {
>> +    ...
>> +*   T array@p[\(0\|1\)];
>> +  };
>> +|
>> +  struct {
>> +    ...
>> +*   T array@p[\(0\|1\)];
>> +  };
>> +|
>> +  union name {
>> +    ...
>> +*   T array@p[\(0\|1\)];
>> +  };
>> +|
>> +  union {
>> +    ...
>> +*   T array@p[\(0\|1\)];
>> +  };
>> +)
>> +
>> +@...ends on patch exists@
> 
> exists is not necessary here.  There are not multiple control-flow paths
> through a structure declaration.
> 
>> +identifier name, array;
>> +type T;
>> +position p : script:python() { relevant(p) };
>> +@@
>> +
>> +(
>> +  struct name {
>> +    ...
>> +    T array@p[
>> +-       0
>> +    ];
>> +  };
>> +|
>> +  struct {
>> +    ...
>> +    T array@p[
>> +-       0
>> +    ];
>> +  };
>> +)
>> +
>> +@...ipt: python depends on report@
>> +p << r.p;
>> +@@
>> +
>> +msg = "WARNING: use flexible-array member instead"
>> +coccilib.report.print_report(p[0], msg)
>> +
>> +@...ipt: python depends on org@
>> +p << r.p;
>> +@@
>> +
>> +msg = "WARNING: use flexible-array member instead"
>> +coccilib.org.print_todo(p, msg)
> 
> This should be coccilib.org.print_todo(p[0], msg)
> 


Thanks, I will send v3 with fixes and proper links to online documentation.

Regards,
Denis