[PATCH v5 2/4] Add system-wide tunables: cache ld.so.cache

[Yury Khrustalev]

On Mon, Mar 02, 2026 at 09:27:16AM -0300, Adhemerval Zanella Netto wrote:
> 
> On 02/03/26 08:05, Yury Khrustalev wrote:
> > On Fri, Feb 27, 2026 at 03:36:26PM -0300, Adhemerval Zanella Netto wrote:
> >>
> >> ...
> >>
> >> I agree with Yury here that we need to add some tests, at least some
> >> minimal one that stress the ld.so.cache reload (which is not the usual
> >> scenario).  I would suggest add test-containts tests that:
> >>
> >>   1. Construct a ld.so.cache, start the test, trigger ld.so.cache
> >>      reconstruct, and check if:
> >>
> >>      1.1. A new entry is used on dlopen.
> >>
> >>      1.2. If removing an entry triggers a dlopen failure.
> >>
> >>      1.3. If not modifying the ld.so.cache contents keep the same
> >>           contents.
> >>
> >>   2. Construct a ld.so.cache, start the test, create a invalid/corrupt
> >>      ld.so.cache and check if the test can load new libraries to
> >>      assure the cached load keeps working.
> > 
> > I appreciate that this is a feature creep which is of course not ideal,
> > however, this is important, so I'm happy to lend a hand to write these
> > tests. DJ, can we co-ordinate this between us?
> 
> Do you mean the feature creep the cached ld.so.cache concept or the extra
> tests required?

I mean that these tests should've been written before this change, so
adding the tests should become a separate patch. Once it's merged, we
can come back here, rebase and continue review.

> The ld.so.cache cache is not strictly required as far I understand. We
> can construct the tunable setup during process startup by merging the 
> system-wide configurations. The tunable_list (dl-tunable-list.h) is marked
> as attribute_relro and I think it makes sense to keep it invariant during
> process startup (so the cache reload should *not* change tunable value).

If ld.so.cache handling is not required for system-wide tunables, then
perhaps we can simplify this patch? I thought it was necessary, maybe I
have misunderstood?

Some tunables are updated during start-up (e.g. while checking all DSO
dependencies). This is not ideal probably.

I agree that tunable values must not change during process lifetime
(after they were merged and (re-)calculated during startup).

Regards,
Yury