[PATCH v4] selftests/bpf: move trampoline_count to dedicated bpf_testmod target

Sun Jian
2026-03-24T04:50:00Z

trampoline_count fills all trampoline attachment slots for a single
target function and verifies that one extra attach fails with -E2BIG.

It currently targets bpf_modify_return_test, which is also used by
other selftests such as modify_return, get_func_ip_test, and
get_func_args_test. When such tests run in parallel, they can contend
for the same per-function trampoline quota and cause unexpected attach
failures. This issue is currently masked by harness serialization.

Move trampoline_count to a dedicated bpf_testmod target and register it
for fmod_ret attachment. Also route the final trigger through
trigger_module_test_read(), so the execution path exercises the same
dedicated target.

This keeps the test semantics unchanged while isolating it from other
selftests, so it no longer needs to run in serial mode. Remove the
TODO comment as well.

Tested:
./test_progs -t trampoline_count -vv
./test_progs -j$(nproc) -t trampoline_count -vv
./test_progs -j$(nproc) -t \
trampoline_count,modify_return,get_func_ip_test,get_func_args_test -vv
20 runs of:
./test_progs -j$(nproc) -t \
trampoline_count,modify_return,get_func_ip_test,get_func_args_test

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
---

Link: https://lore.kernel.org/bpf/20260320074150.628094-1-sun.jian.kdev@gmail.com/

v4:
- simplify the dedicated trampoline_count target and its trigger path
- simplify the associated fentry/fmod_ret/fexit test program signatures
- reduce the final trigger to a plain ASSERT_OK()
- drop Suggested-by per Jiri

v3:
- route the final trigger through trigger_module_test_read() and make
bpf_testmod_test_read() call the dedicated trampoline_count target

v2:
- rewrite the subject to describe the change
- resend with the correct patch content

.../bpf/prog_tests/trampoline_count.c | 17 +++--------------
.../bpf/progs/test_trampoline_count.c | 12 ++++++------
.../selftests/bpf/test_kmods/bpf_testmod.c | 18 ++++++++++++++++++
3 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
index 6cd7349d4a2b..7321850db75f 100644
--- a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
+++ b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
@@ -30,16 +30,14 @@ static struct bpf_program *load_prog(char *file, char *name, struct inst *inst)
return prog;
}

-/* TODO: use different target function to run in concurrent mode */
-void serial_test_trampoline_count(void)
+void test_trampoline_count(void)
{
char *file = "test_trampoline_count.bpf.o";
char *const progs[] = { "fentry_test", "fmod_ret_test", "fexit_test" };
- int bpf_max_tramp_links, err, i, prog_fd;
+ int bpf_max_tramp_links, i;
struct bpf_program *prog;
struct bpf_link *link;
struct inst *inst;
- LIBBPF_OPTS(bpf_test_run_opts, opts);

bpf_max_tramp_links = get_bpf_max_tramp_links();
if (!ASSERT_GE(bpf_max_tramp_links, 1, "bpf_max_tramp_links"))
@@ -80,16 +78,7 @@ void serial_test_trampoline_count(void)
goto cleanup;

/* and finally execute the probe */
- prog_fd = bpf_program__fd(prog);
- if (!ASSERT_GE(prog_fd, 0, "bpf_program__fd"))
- goto cleanup;
-
- err = bpf_prog_test_run_opts(prog_fd, &opts);
- if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
- goto cleanup;
-
- ASSERT_EQ(opts.retval & 0xffff, 33, "bpf_modify_return_test.result");
- ASSERT_EQ(opts.retval >> 16, 2, "bpf_modify_return_test.side_effect");
+ ASSERT_OK(trigger_module_test_read(256), "trigger_module_test_read");

cleanup:
for (; i >= 0; i--) {
diff --git a/tools/testing/selftests/bpf/progs/test_trampoline_count.c b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
index 7765720da7d5..02f52806b1b2 100644
--- a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
+++ b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
@@ -3,20 +3,20 @@
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

-SEC("fentry/bpf_modify_return_test")
-int BPF_PROG(fentry_test, int a, int *b)
+SEC("fentry/bpf_testmod_trampoline_count_test")
+int BPF_PROG(fentry_test)
{
return 0;
}

-SEC("fmod_ret/bpf_modify_return_test")
-int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
+SEC("fmod_ret/bpf_testmod_trampoline_count_test")
+int BPF_PROG(fmod_ret_test, int ret)
{
return 0;
}

-SEC("fexit/bpf_modify_return_test")
-int BPF_PROG(fexit_test, int a, int *b, int ret)
+SEC("fexit/bpf_testmod_trampoline_count_test")
+int BPF_PROG(fexit_test, int ret)
{
return 0;
}
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index e62c6b78657f..9caf9ffa1bb0 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -470,6 +470,11 @@ noinline void bpf_testmod_stacktrace_test_1(void)

int bpf_testmod_fentry_ok;

+noinline int bpf_testmod_trampoline_count_test(void)
+{
+ return 0;
+}
+
noinline ssize_t
bpf_testmod_test_read(struct file *file, struct kobject *kobj,
const struct bin_attribute *bin_attr,
@@ -548,6 +553,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
21, 22, 23, 24, 25, 26) != 231)
goto out;

+ bpf_testmod_trampoline_count_test();
+
bpf_testmod_stacktrace_test_1();

bpf_testmod_fentry_ok = 1;
@@ -1843,6 +1850,16 @@ struct bpf_struct_ops testmod_multi_st_ops = {

extern int bpf_fentry_test1(int a);

+BTF_KFUNCS_START(bpf_testmod_trampoline_count_ids)
+BTF_ID_FLAGS(func, bpf_testmod_trampoline_count_test)
+BTF_KFUNCS_END(bpf_testmod_trampoline_count_ids)
+
+static const struct
+btf_kfunc_id_set bpf_testmod_trampoline_count_fmodret_set = {
+ .owner = THIS_MODULE,
+ .set = &bpf_testmod_trampoline_count_ids,
+};
+
static int bpf_testmod_init(void)
{
const struct btf_id_dtor_kfunc bpf_testmod_dtors[] = {
@@ -1859,6 +1876,7 @@ static int bpf_testmod_init(void)
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_testmod_kfunc_set);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_testmod_kfunc_set);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_testmod_kfunc_set);
+ ret = ret ?: register_btf_fmodret_id_set(&bpf_testmod_trampoline_count_fmodret_set);
ret = ret ?: register_bpf_struct_ops(&bpf_bpf_testmod_ops, bpf_testmod_ops);
ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops2, bpf_testmod_ops2);
ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops3, bpf_testmod_ops3);

base-commit: 8a30aeb0d1b4e4aaf7f7bae72f20f2ae75385ccb
--
2.43.0