selftests/bpf: Add test for struct_ops __ref argument in any position

2026-03-24T15:51:23+00:00

Add a selftest to verify that the verifier correctly identifies refcounted arguments in struct_ops programs, even when they are not the first argument. This ensures that the restriction on tail calls for programs with __ref arguments is properly enforced regardless of which argument they appear in. This test verifies the fix for check_struct_ops_btf_id() proposed by Keisuke Nishimura [0], which corrected a bug where only the first argument was checked for the refcounted flag. The test includes: - An update to bpf_testmod to add 'test_refcounted_multi', an operator with three arguments where the third is tagged with "__ref". - A BPF program 'test_refcounted_multi' that attempts a tail call. - A test runner that asserts the verifier rejects the program with "program with __ref argument cannot tail call". [0]: https://lore.kernel.org/bpf/20260320130219.63711-1-keisuke.nishimura@inria.fr/ Signed-off-by: Varun R Mallya Link: https://lore.kernel.org/r/20260321214038.80479-1-varunrmallya@gmail.com Signed-off-by: Alexei Starovoitov

lwn.git/tools/testing/selftests/bpf/progs/struct_ops_multi_args.c, branch master

selftests/bpf: Add test for struct_ops __ref argument in any position