Re: [PATCH 2/3] module: make structure definitions always visible

[Daniel Gomez <da.gomez@kernel.org>]

On 12/06/2025 16.53, Thomas WeiÃschuh wrote:
> To write code that works with both CONFIG_MODULES=y and CONFIG_MODULES=n
> it is convenient to use "if (IS_ENABLED(CONFIG_MODULES))" over raw #ifdef.
> The code will still fully typechecked but the unreachable parts are
> discarded by the compiler. This prevents accidental breakage when a certain
> kconfig combination was not specifically tested by the developer.
> This pattern is already supported to some extend by module.h defining
> empty stub functions if CONFIG_MODULES=n.
> However some users of module.h work on the structured defined by module.h.
> 
> Therefore these structure definitions need to be visible, too.

We are missing here which structures are needed. + we are making more things
visible than what we actually need.

> 
> Many structure members are still gated by specific configuration settings.
> The assumption for those is that the code using them will be gated behind
> the same configuration setting anyways.

I think code and kconfig need to reflect the actual dependencies. For example,
if CONFIG_LIVEPATCH depends on CONFIG_MODULES, we need to specify that in
Kconfig with depends on, as well as keep the code gated by these 2 configs with
ifdef/IS_ENABLED.

> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
>  include/linux/module.h | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 52f7b0487a2733c56e2531a434887e56e1bf45b2..7f783e71636542b99db3dd869a9387d14992df45 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -302,17 +302,6 @@ static typeof(name) __mod_device_table__##type##__##name		\
>  
>  struct notifier_block;
>  
> -#ifdef CONFIG_MODULES
> -
> -extern int modules_disabled; /* for sysctl */
> -/* Get/put a kernel symbol (calls must be symmetric) */
> -void *__symbol_get(const char *symbol);
> -void *__symbol_get_gpl(const char *symbol);
> -#define symbol_get(x)	({ \
> -	static const char __notrim[] \
> -		__used __section(".no_trim_symbol") = __stringify(x); \
> -	(typeof(&x))(__symbol_get(__stringify(x))); })
> -
>  enum module_state {
>  	MODULE_STATE_LIVE,	/* Normal state. */
>  	MODULE_STATE_COMING,	/* Full formed, running module_init. */
> @@ -598,6 +587,18 @@ struct module {
>  	struct _ddebug_info dyndbg_info;
>  #endif
>  } ____cacheline_aligned __randomize_layout;
> +
> +#ifdef CONFIG_MODULES
> +
> +extern int modules_disabled; /* for sysctl */
> +/* Get/put a kernel symbol (calls must be symmetric) */
> +void *__symbol_get(const char *symbol);
> +void *__symbol_get_gpl(const char *symbol);
> +#define symbol_get(x)	({ \
> +	static const char __notrim[] \
> +		__used __section(".no_trim_symbol") = __stringify(x); \
> +	(typeof(&x))(__symbol_get(__stringify(x))); })
> +

The patch exposes data structures that are not needed. + breaks the
config dependencies.

For example, before this patch:

#ifdef CONFIG_MODULES

{...}

struct mod_tree_node {

{...}

struct module_memory {
	void *base;
	bool is_rox;
	unsigned int size;

#ifdef CONFIG_MODULES_TREE_LOOKUP
	struct mod_tree_node mtn;
#endif
};

{...}
#endif /* CONFIG_MODULES */

After the patch, mod_tree_node is not needed externally. And the mtn field
in module_memory is exposed only under MODULES_TREE_LOOKUP and not MODULES
+ MODULES_TREE_LOOKUP.

I general, I see the issues I mentioned with LIVEPATCH, mod_tree_node, macros,
and LOOKUP.

>  #define MODULE_ARCH_INIT {}
>  #endif
>