[PATCH v5 14/16] modules: Support extended MODVERSIONS info

[Luis Chamberlain]

On Thu, Oct 17, 2024 at 02:08:19PM +0200, Helge Deller wrote:
> Hi Luis,
> 
> On 10/17/24 01:21, Luis Chamberlain wrote:
> > That sounds great. Yeah, the above would be great to test. A while ago
> > I wrote a new modules selftests in order to test possible improvements
> > on find_symbol() but I also did this due to push the limits of the
> > numbers of symbols we could support. I wrote all this to also test the
> > possible 64-bit alignment benefits of __ksymtab_ sections on
> > architectures without CONFIG_HAVE_ARCH_PREL32_RELOCATIONS (e.g. ppc64,
> > ppc64le, parisc, s390x,...). [....]
> > 
> > I forget what we concluded on Helge Deller's alignement patches, I think
> > there was an idea on how to address the alignment through other means.
> > 
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git/log/?h=20241016-modules-symtab
> 
> I stumbled upon the unaligned-memory-access.rst document [1].
> Please read it, as it is a really good document, and the section
> "Why unaligned access is bad" states:
> It should be obvious from the above that if your code causes unaligned
> memory accesses to happen, your code will not work correctly on certain
> platforms and will cause performance problems on others.
> 
> With this in mind, you really should apply both of my alignment
> patches which you currently carry in [0].
> 
> For parisc I partly solved the issue by fixing the arch-specific kernel unalignment
> handler, but every time module sections are stored unaligned, it triggers
> performance degregation on parisc (and other sensitive platforms).
> 
> I suggest you apply them unconditionally.
> 
> Helge
> 
> [1]  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/core-api/unaligned-memory-access.rst

You're right, I've just referred to that doc and pushed to the new
linux modules [2] modules-next branch. This is also great timing so
that the work that is ongoing for Rust will take this into
consideration as well. I'll just post the test I wrote as separate
thing but it surely can be used to help test some of this later.

[2] git://git.kernel.org/pub/scm/linux/kernel/git/modules/linux.git

  Luis