Re: [PATCH v8 30/43] dyndbg: check DYNAMIC_DEBUG_CLASSMAP_{DEFINE,USE_} args at compile-time

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Compile-time check incorrectly rejects valid class ID 62 due to an off-by-one error in the upper bound assertion.
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commit eff2fbed05187c69eca3bc170f67e07db2c41b8d
Author: Jim Cromie <jim.cromie@gmail.com>

dyndbg: check DYNAMIC_DEBUG_CLASSMAP_{DEFINE,USE_} args at compile-time

This commit adds the __DYNAMIC_DEBUG_CLASSMAP_CHECK macro to implement
compile-time argument checks for dynamic debug classmaps. These assertions
validate bounds for the base offset, class names length, and map types to
prevent simple misuses.

> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index 17fc3a29d97b8..471b9891bd83b 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -197,6 +197,19 @@ struct ddebug_class_param {
>   * __pr_debug_cls(22, "no such class"); compiles but is not reachable
>   */
>  
> +#define __DYNAMIC_DEBUG_CLASSMAP_CHECK(_clnames, _base, _mapty)		\
> +	static_assert(((_base) >= 0 && (_base) < _DPRINTK_CLASS_DFLT),	\
> +		      "_base must be in 0..62");			\
> +	static_assert(__DDEBUG_ARRAY_SIZE(_clnames) > 0,				\
> +		      "classnames array size must be > 0");		\
> +	static_assert(__DDEBUG_ARRAY_SIZE(_clnames) <= 32,			\
> +		      "classnames array size must be <= 32");		\
> +	static_assert((__DDEBUG_ARRAY_SIZE(_clnames) + (_base)) < _DPRINTK_CLASS_DFLT, \
> +		      "_base + classnames.length must be <= 62");	\

[Severity: Low]
Does this logic introduce an off-by-one error that inadvertently rejects
valid class maps?

The first static assertion correctly allows a base up to 62 by verifying
it is less than _DPRINTK_CLASS_DFLT. 

However, if a class map is defined with a single class at a base of 62, the
sum of the base and array size evaluates to 63. Since this check strictly
enforces that the sum must be less than _DPRINTK_CLASS_DFLT (meaning <= 62), 
it would fail compilation.

Should this assertion allow the sum to be equal to _DPRINTK_CLASS_DFLT 
to permit a single class definition at the highest allowed base?

> +	static_assert(((_mapty) >= DD_CLASS_TYPE_DISJOINT_BITS) &&	\
> +		      ((_mapty) <= DD_CLASS_TYPE_LEVEL_NUM),		\
> +		      "unknown class_map_type")
> +

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Sashiko AI review · https://sashiko.dev/#/patchset/20260905-dd-cmap-part2-clean-v8-0-a4cc0674f6fd@gmail.com?part=30