Subject: ARM: mm: Could I change module space size or place modules in vmalloc area?

From: [email-masked] (Arnd Bergmann)
Date: Fri, 3 Jan 2014 14:23:55 +0100

On Friday 03 January 2014, Russell King - ARM Linux wrote:
> On Fri, Jan 03, 2014 at 01:10:09PM +0100, Arnd Bergmann wrote:
> > Aside from the good comments that Russell made, I would remark that the
> > fact that you need multiple megabytes worth of modules indicates that you
> > are doing something wrong. Can you point to a git tree containing those
> > modules?
> 
> From the comments which have been made, one point that seems to have
> been identified is that if this module is first stripped and then
> loaded, it can load, but if it's unstripped, it's too big.  This sounds
> suboptimal to me - the debug info shouldn't be loaded into the kernel.

Reading the layout_and_allocate() function, that is probably the
intention already, and if something goes wrong there on ARM, it could be
fixed up in an arch specific module_frob_arch_sections() function.

> However, I guess there's bad interactions with module signing if you
> don't do this and the module was signed with the debug info present,
> so I don't think there's a good solution for this.

My point was another anyway: I can't think of any good reason why
you would end up with this many modules on any sane system. The only
cases I've seen so far are

- modules written in C++, with libstdc++ linked into the module
- a closed-source platform port hidden in a loadable module that
  contains all the device drivers and subsystems while ignoring the
  infrastructure we have in the kernel, and the possible legal
  implications.
- a bug in the module using large arrays that should just be
  dynamically allocated.
- device firmware statically linked into the module rather than
  loaded using request_firmware.

In each of these cases, the real answer is to fix the code they are
trying to load to do things in a more common way, especially if the
intention is to eventually merge the code upstream. It is of course
possible that they are indeed trying something valid, that's why
I asked to see the source code.

	Arnd