linux-kernel - Re: [PATCH v3 20/54] dyndbg: check DYNAMIC_DEBUG_CLASSMAP

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Message-ID: <ca082495-0df0-432d-8269-d51525f8795a@bootlin.com>
Date: Wed, 16 Apr 2025 08:54:19 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: jim.cromie@...il.com
Cc: jbaron@...mai.com, gregkh@...uxfoundation.org, ukaszb@...omium.org,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 amd-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, daniel.vetter@...ll.ch,
 tvrtko.ursulin@...ux.intel.com, jani.nikula@...el.com,
 ville.syrjala@...ux.intel.com
Subject: Re: [PATCH v3 20/54] dyndbg: check DYNAMIC_DEBUG_CLASSMAP_DEFINE args
 at compile-time



Le 15/04/2025 à 21:54, jim.cromie@...il.com a écrit :
> On Tue, Apr 15, 2025 at 4:04 AM Louis Chauvet <louis.chauvet@...tlin.com> wrote:
>>
>>
>>
>> Le 02/04/2025 à 19:41, Jim Cromie a écrit :
>>> Add __DYNAMIC_DEBUG_CLASSMAP_CHECK to implement the following
>>> arg-checks at compile-time:
>>>
>>>        0 <= _base < 63
>>>        class_names is not empty
>>>        class_names[0] is a string
>>
>> I don't see where this is checked, did I miss something?
> 
> kinda/sorta ?   theres no explicit check for "string".
> BUT
> this would fail, cuz 1 doesnt fit into a char* arr[0]

You are totally right, I was looking for a static_assert, but the 
compiler do some checks too, sorry!

>>> +DYNDBG_CLASSMAP_DEFINE(fail_str_type, 0, 0, 1 /* not a string */);
> 
> Im perhaps over-simplifying the description
> 
>>
>>>        (class_names.length + _base) < 63
>>>
>>> These compile-time checks will prevent several misuses; 4 such
>>> examples are added to test_dynamic_debug_submod.ko, and will fail
>>> compilation if -DDD_MACRO_ARGCHECK is added to cflags.  This wouldn't
>>> be a useful CONFIG_ item, since it breaks the build.
>>>
>>> Signed-off-by: Jim Cromie <jim.cromie@...il.com>
>>> ---
>>> v3- $macro_name =~ s/DYNDBG/DYNAMIC_DEBUG/
>>>
>>> prev-
>>> - split static-asserts to __DYNDBG_CLASSMAP_CHECK
>>> - move __DYNDBG_CLASSMAP_CHECK above kdoc for DYNDBG_CLASSMAP_DEFINE
>>>     silences kernel-doc warnings
>>> ---
>>>    include/linux/dynamic_debug.h |  9 +++++++++
>>>    lib/test_dynamic_debug.c      | 11 +++++++++++
>>>    2 files changed, 20 insertions(+)
>>>
>>> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
>>> index 9af825c84e70..4941ef2adb46 100644
>>> --- a/include/linux/dynamic_debug.h
>>> +++ b/include/linux/dynamic_debug.h
>>> @@ -99,6 +99,14 @@ struct _ddebug_class_map {
>>>        enum ddebug_class_map_type map_type;
>>>    };
>>>
>>> +#define __DYNAMIC_DEBUG_CLASSMAP_CHECK(_clnames, _base)                      \
>>> +     static_assert(((_base) >= 0 && (_base) < _DPRINTK_CLASS_DFLT),  \
>>> +                   "_base must be in 0..62");                        \
>>> +     static_assert(ARRAY_SIZE(_clnames) > 0,                         \
>>> +                   "classnames array size must be > 0");             \
>>> +     static_assert((ARRAY_SIZE(_clnames) + (_base)) < _DPRINTK_CLASS_DFLT, \
>>> +                   "_base + classnames.length exceeds range")
>>> +
>>>    /**
>>>     * DYNAMIC_DEBUG_CLASSMAP_DEFINE - define debug classes used by a module.
>>>     * @_var:   name of the classmap, exported for other modules coordinated use.
>>> @@ -112,6 +120,7 @@ struct _ddebug_class_map {
>>>     */
>>>    #define DYNAMIC_DEBUG_CLASSMAP_DEFINE(_var, _mapty, _base, ...)             \
>>>        static const char *_var##_classnames[] = { __VA_ARGS__ };       \
>>
>> Or maybe it was already enforced by this, but in this case the commit
>> message contains too much checks.
>>
>>> +     __DYNAMIC_DEBUG_CLASSMAP_CHECK(_var##_classnames, (_base));     \
>>>        extern struct _ddebug_class_map _var;                           \
>>>        struct _ddebug_class_map __aligned(8) __used                    \
>>>                __section("__dyndbg_class_maps") _var = {               \
>>> diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
>>> index e42916b08fd4..9f9e3fddd7e6 100644
>>> --- a/lib/test_dynamic_debug.c
>>> +++ b/lib/test_dynamic_debug.c
>>> @@ -146,8 +146,19 @@ DYNDBG_CLASSMAP_DEFINE(classid_range_conflict, 0, D2_CORE + 1, "D3_CORE");
>>>    DYNAMIC_DEBUG_CLASSMAP_USE(map_disjoint_bits);
>>>    DYNAMIC_DEBUG_CLASSMAP_USE(map_level_num);
>>>
>>> +#if defined(DD_MACRO_ARGCHECK)
>>> +/*
>>> + * Exersize compile-time arg-checks in DYNDBG_CLASSMAP_DEFINE.
>>> + * These will break compilation.
>>> + */
>>> +DYNDBG_CLASSMAP_DEFINE(fail_base_neg, 0, -1, "NEGATIVE_BASE_ARG");
>>> +DYNDBG_CLASSMAP_DEFINE(fail_base_big, 0, 100, "TOOBIG_BASE_ARG");
>>> +DYNDBG_CLASSMAP_DEFINE(fail_str_type, 0, 0, 1 /* not a string */);
>>> +DYNDBG_CLASSMAP_DEFINE(fail_emptyclass, 0, 0 /* ,empty */);
>>>    #endif
>>>
>>> +#endif /* TEST_DYNAMIC_DEBUG_SUBMOD */
>>> +
>>>    /* stand-in for all pr_debug etc */
>>>    #define prdbg(SYM) __pr_debug_cls(SYM, #SYM " msg\n")
>>>
>>
>> --
>> Louis Chauvet, Bootlin
>> Embedded Linux and Kernel engineering
>> https://bootlin.com
>>
>>

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com