Merge branch 'bpf-allow-union-argument-in-trampoline-based-programs'

Merge branch 'bpf-allow-union-argument-in-trampoline-based-programs'

Leon Hwang says:

====================
bpf: Allow union argument in trampoline based programs

While tracing 'release_pages' with bpfsnoop[0], the verifier reports:

The function release_pages arg0 type UNION is unsupported.

However, it should be acceptable to trace functions that have 'union'
arguments.

This patch set enables such support in the verifier by allowing 'union'
as a valid argument type.

Changes:
v3 -> v4:
* Address comments from Alexei:
  * Trim bpftrace output in patch #1 log.
  * Drop the referenced commit info and the test output in patch #2 log.

v2 -> v3:
* Address comments from Alexei:
  * Reuse the existing flag BTF_FMODEL_STRUCT_ARG.
  * Update the comment of the flag BTF_FMODEL_STRUCT_ARG.

v1 -> v2:
* Add 16B 'union' argument support in x86_64 trampoline.
* Update selftests using bpf_testmod.
* Add test case about 16-bytes 'union' argument.
* Address comments from Alexei:
  * Study the patch set about 'struct' argument support.
  * Update selftests to cover more cases.
v1: https://lore.kernel.org/bpf/20250905133226.84675-1-leon.hwang@linux.dev/

Links:
[0] https://github.com/bpfsnoop/bpfsnoop
====================

Link: https://patch.msgid.link/20250919044110.23729-1-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>