is there an efficient module_is_builtin() test ?

is there an efficient module_is_builtin() test ?

[jim.cromie]

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Im trying to reduce memory used by
internal tables built into DYNAMIC_DEBUG

the main savings available is in the per pr_debug*
callsite data: modname, filename, funcname.

I have segregated those fields to a new __dyndbg_sites section,
described by struct _ddebug_site, and now refd by new ptr in
struct _ddebug

That new ptr enlarges the memory footprint, so I want to replace it
with an integer index into the section / array.  Existing padding could
hold the index.

To use the index, I need  &dyndbg_sites[], and that only works
for builtin-module's callsites.   For loaded modules, I can/have
added a pointer to the section into module load_info, giving me
the base I will need for the ! builtin branch.

I just need a not expensive  is-it-builtin (modref)

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Re: is there an efficient module_is_builtin() test ?

[Valdis Klētnieks]

On Tue, 09 Mar 2021 12:55:14 -0700, jim.cromie@gmail.com said:

> To use the index, I need  &dyndbg_sites[], and that only works
> for builtin-module's callsites.   For loaded modules, I can/have
> added a pointer to the section into module load_info, giving me
> the base I will need for the ! builtin branch.
>
> I just need a not expensive  is-it-builtin (modref)

One way to sidestep it is to stick in an EXPORT_SYMBOL(dyndbg_sites)
in the .c file you're defining it, and let the module loader do all the heavy
lifting for you. Not sure if some license purist would insist on EXPORT_SYMBOL_GPL
instead - the difference will only matter for out-of-tree non-GPL modules.

An slightly uglier solution is to do something like

#if defined(MODULE)
#define FIND_DEBUG /* code to find via load_info */
#else
#define FIND_DEBUG /* code to load &dyndbg_site directly */
#endif

which you should probably stick into a suitable .h file, and then
stick your newly defined FIND_DEBUG where you need the magic
happen (probably in a .h file as well)

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Re: is there an efficient module_is_builtin() test ?

[jim.cromie]

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On Tue, Mar 9, 2021 at 3:25 PM Valdis Klētnieks <valdis.kletnieks@vt.edu>
wrote:

> On Tue, 09 Mar 2021 12:55:14 -0700, jim.cromie@gmail.com said:
>
> > To use the index, I need  &dyndbg_sites[], and that only works
> > for builtin-module's callsites.   For loaded modules, I can/have
> > added a pointer to the section into module load_info, giving me
> > the base I will need for the ! builtin branch.
> >
> > I just need a not expensive  is-it-builtin (modref)
>

thanks Valdis, the back and forth helped.

So, to follow up, the above is embodied here;
https://lore.kernel.org/lkml/20210316050801.2446401-1-jim.cromie@gmail.com/
in the add index patch, near 13/18

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