Hi Ludo,

On Thu, 10 Sep 2020 18:26:57 +0200
Ludovic Courtès <ludovic.courtes@inria.fr> wrote:

> > 150 MB a2fs24bgghjvlzq5lzr6zki7mqxx8mpi-linux-libre-module-builder-5.8.7/lib/modules/build/drivers/gpu/drm/amd/include/asic_reg
> > 30 MB a2fs24bgghjvlzq5lzr6zki7mqxx8mpi-linux-libre-module-builder-5.8.7/lib/modules/build/drivers/staging
> >
> > I don't think we need these in any potential Linux kernel module--but who
> > knows?  Maybe somebody does need those.  
> 
> So, I can think of the following ways to address that:
> 
>   1. Remove for example *.c, assuming the out-of-tree modules we package
>      only care about *.h + build machinery.

The biggest source files, see above, are header files
(drivers/gpu/drm/amd/include/asic_reg).

>   2. Don’t add all of the Linux source to the store, or at least not
>      under a new name each time.  One way to do that would be to unpack
>      the Linux-libre tree within the build tree of the out-of-tree
>      module.  We’d be reducing GC stress at the expense of a
>      (reasonable?) increase in module build time.

And patch it correctly etc just like make-linux-libre does?  That doesn't
sound safe.  The current setup is basically inheriting from the package
make-linux-libre gave us and changing the 'build phase slightly.  That means
it will be exactly the same otherwise.

The only way to reduce effort safely is to delete the set of source
files (especially header files) which we don't need for out-of-tree
modules.

I checked--that would reduce the size of linux-libre-builder by about 800 MB
(to 255 MB; see [1][2]).
That would mean that some modules can't be out-of-tree.  But I guess
that's okay--and we could not-delete some files later if need be.

Btw, linux-libre is currently not reproducible--see bug 43301.
That could introduce a security problem if the Linux kernel and
an out-of-tree module are compiled differently (they are) and then loaded
into the same kernel (even now).

[1] Toplevel files in linux-libre-module-builder would be then (sizes are included if size > 1 MB):

arch/   (134 MB)
block/  (2 MB)
certs/
COPYING
CREDITS
crypto/ (4 MB)
include/ (59 MB)
init/
ipc/
Kbuild
Kconfig
kernel/ (11 MB)
lib/ (6 MB)
LICENSES/
MAINTAINERS
Makefile
mm/ (5 MB)
Module.symvers (2 MB)
README
scripts/ (6 MB)
security/ (4 MB)
System.map (5 MB)
tools/ (14 MB)
usr/
virt/

[2] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=43332