Re: [PATCH v2 13/21] modpost: emit module descriptors as assembly

[Lorenzo Stoakes (ARM)]

On Mon, Sep 21, 2026 at 02:36:30PM +0200, Petr Pavlu wrote:
> On 9/21/26 1:57 PM, Lorenzo Stoakes (ARM) wrote:
> > (note there's a v3 see [0])
> >
> > [0]: https://lore.kernel.org/linux-kbuild/20260917-build-speedup-v3-0-9ecf4163ff36@xxxxxxxxxx/
>
> Thanks, I missed it.
>
> > On Mon, Sep 21, 2026 at 01:25:09PM +0200, Petr Pavlu wrote:
> >> On 9/14/26 11:22 AM, Lorenzo Stoakes (ARM) wrote:
> >>> The sections were confirmed to be byte-for-byte identical to the C version
> >>> produced - each of .modinfo, .gnu.linkonce.this_module, __ksymtab*,
> >>> __ksymtab_strings, __kcrctab*, __kflagstab*, __versions,
> >>> __version_ext_crcs, __version_ext_names and their relocations - for all
> >>> 8,135 modules of a clang allmodconfig build with CONFIG_COMPILE_TEST off
> >>> and CONFIG_MODVERSIONS, CONFIG_EXTENDED_MODVERSIONS and
> >>> CONFIG_MODULE_SRCVERSION_ALL on, and for a sample built with gcc.
> >>
> >> Lowering the data to assembly loses debug information for __this_module,
> >> specifically that it has type `struct module`. It might be worth
> >
> > No, it keeps it - every module includes linux/module.h, and the extern
> > declaration of __this_module carries the type, so all of the stuff gdb
> > needs (e.g. ptype, p & field access), DWARF etc. is all there in the same
> > way as with .mod.c.
> >
> > Have confirmed locally.
>
> An extern declaration alone shouldn't cause its name and type to be
> included in debug information. They should appear only when the variable
> is referenced by some code.

Ack yeah sorry my mistake, I had the LLM check that and should have known
better than to trust it without reviewing what it said (as I have done for
the most part for everything in this series).

>
> Testing with a simple module that previously referenced __this_module
> only in .mod.c and in no other file, such as lib/test_module.c, shows
> that the .ko no longer contains debug information for this variable.
>
> I've verified this behavior with GCC 16 and Clang 19.

Ack confirmed locally.

Can put a fix in module-common.c.

The LLM came up with a reference as an alternative:

static struct module *const __this_module_dbg __used __section(".discard.this_module") = &__this_module;

Would that work? Or should we go with your original suggestion? -

__weak __section(".discard.this_module") struct module __this_module;

>
> --
> Cheers,
> Petr

--
Cheers, Lorenzo