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

[Petr Pavlu]

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.

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.

-- 
Cheers,
Petr