selftests/bpf: Use the correct destructor kfunc type

With CONFIG_CFI_CLANG enabled, the kernel strictly enforces that
indirect function calls use a function pointer type that matches the
target function. As bpf_testmod_ctx_release() signature differs from
the btf_dtor_kfunc_t pointer type used for the destructor calls in
bpf_obj_free_fields(), add a stub function with the correct type to
fix the type mismatch.

Signed-off-by: Sami Tolvanen <[email protected]>

Author: samitolvanen

tools/testing/selftests/bpf/test_kmods/bpf_testmod.c

@@ -249,6 +249,13 @@ __bpf_kfunc void bpf_testmod_ctx_release(struct bpf_testmod_ctx *ctx)
 		call_rcu(&ctx->rcu, testmod_free_cb);
 }
 
+__used __retain void __bpf_testmod_ctx_release(void *ctx)
+{
+	bpf_testmod_ctx_release(ctx);
+}
+
+CFI_NOSEAL(__bpf_testmod_ctx_release);
+
 static struct bpf_testmod_ops3 *st_ops3;
 
 static int bpf_testmod_test_3(void)
@@ -631,7 +638,7 @@ BTF_KFUNCS_END(bpf_testmod_common_kfunc_ids)
 
 BTF_ID_LIST(bpf_testmod_dtor_ids)
 BTF_ID(struct, bpf_testmod_ctx)
-BTF_ID(func, bpf_testmod_ctx_release)
+BTF_ID(func, __bpf_testmod_ctx_release)
 
 static const struct btf_kfunc_id_set bpf_testmod_common_kfunc_set = {
 	.owner = THIS_MODULE,