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

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Message-ID: <428d9ffb-70bb-42f3-bf4e-416cfd90f88c@bootlin.com>
Date: Tue, 15 Apr 2025 12:04:11 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Jim Cromie <jim.cromie@...il.com>, jbaron@...mai.com,
 gregkh@...uxfoundation.org, ukaszb@...omium.org, linux-kernel@...r.kernel.org
Cc: 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 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?

> 	(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