Re: [PATCH 15/23] modpost: emit module descriptors as assembly

[Linus Torvalds]

On Tue, 8 Sept 2026 at 13:58, Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx> wrote:
>
> modpost generates a descriptor for every module in the form of a
> <module>.mod.c file with .modinfo strings, the __this_module descriptor,
> exported symbol tables and (with CONFIG_MODVERSIONS set), the CRC of
> imported symbols.
>
> These files are compiled like any other kernel C file with all of the
> -include preamble, as well as including linux/module.h, header dependencies
> generated by fixdep of a few hundred headers, an objtool run and if LTO is
> being performed, a link is performed to generate native code.

This kind of triggers the same reaction as the kallsyms code: I think
not including <linux/module.h> is probably the biggest win in this
all, and precomputing the offsets of the (few) structures that modpost
uses then makes the whole end result fairly trivial in raw asm.

Fine.

BUT.

You end up with things like this instead:

> diff --git a/scripts/mod/module-offsets.c b/scripts/mod/module-offsets.c

where it generates a header file for those asm scripts so that the asm
generation can do things like

        buf_printf(buf, "\t.size __this_module, %d\n",
MOD_SIZEOF_struct_module);

etc.

But I - again - get the feeling that this is all going through AS as a
silly way to generate an object file, and that there really isn't any
obvious advantage to that side quest.

Becuase no human ever wants to see that asm file, and it's no more
legible than generating the object file directly would have been.

So I get the feeling that it would again be more natural to just
generate the object file directly when all those files really end up
being are a few symbol definitions and a couple of fixed structures
(is there anything but the magic "__this_module" thing and the modinfo
unique ID thing?)

And again - I feel like nobody sane would want to write that code. I
certainly don't. But if this was at least partly automated anyway,
going that extra step might not be all that horrific.

I'll also be honest: part of why I do these suggestions is that I do
think it would be faster to skip the intermediate assembler step, but
a big part of it is that I don't love the random turds our build
creates. Getting rid of the *.mod.c files would be a cleanup of our
strange build.

             Linus