Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add trampolines single and multi-level pointer params test coverage

[Slava Imameev <slava.imameev@crowdstrike.com>]

On Tue, 03 Mar 2026 12:08:44, Eduard Zingerman wrote:
> On Tue, 2026-03-03 at 20:54 +1100, Slava Imameev wrote:
> > Single and multi-level pointer params and return value test coverage
> > for BPF trampolines:
> > - fentry/fexit programs covering struct and void double/triple
> >   pointer parameters and return values
> > - verifier context tests covering pointers as parameters, these
> >   tests cover single and double pointers to int, enum 32 and 64,
> >   void, function, and double pointers to struct, triple pointers
> >   for void
> > - verifier context tests covering single and double pointers to
> >   float, to check proper error is returned as pointers to float
> >   are not supported
> > - verifier context tests covering pointers as return values
> > - verifier context tests for lsm to check trusted parameters
> >   handling
> > - verifier context tests covering out-of-bound access after cast
> > - verifier BPF helper tests to validate no change in verifier
> >   behavior
> > 
> > Signed-off-by: Slava Imameev <slava.imameev@crowdstrike.com>
> > ---
> 
> Again, I probably miss a point, but with current implementation it
> seems sufficient in verifier_ctx_ptr_param() to add one or two
> tests accessing void** or similar and checking verification log
> to validate that parameter has expected type scalar().
> Why so many tests are necessary?

This reflects my belief in more comprehensive test coverage.

I can certainly reduce the number of tests if this seems excessive,
but I made 90% of the added tests one-liners to keep them maintainable.

These changes add support for multilevel pointers, so double and
triple pointers need to be checked at minimum. I think adding checks
for any new type support is beneficial. I tried to verify a broader
set of conditions that might be broken by future changes. I tried to
make most tests one-liners to facilitate future modification.