Re: [PATCH bpf v2] selftests/bpf: Use both hrtimer enqueue helpers in vmlinux test

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, May 08, 2026 at 05:57:30PM -0700, Ihor Solodrai wrote:
> The vmlinux selftest triggers nanosleep and checks that both kprobe
> and fentry programs observe the hrtimer enqueue path.
> 
> After the hrtimer_start_expires_user() conversion [1], nanosleep
> reaches hrtimer_start_range_ns_user() instead of
> hrtimer_start_range_ns(). Hard-coding either symbol makes the test
> fail either on bpf tree or on linux-next [2].
> 
> Update the test to resolve the target symbol at runtime via
> libbpf_find_vmlinux_btf_id(). This is a nice example of how to modify
> a BPF program to work on both older and newer kernel revision.

iiuc this will help before the [1] fully propagates everywhere,
also good as an example

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> 
> [1] https://lore.kernel.org/all/20260408114952.062400833@kernel.org/
> [2] https://github.com/kernel-patches/bpf/actions/runs/25485909958/job/74782902203
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
> 
> ---
> 
> v1->v2:
>   * Use bpf_program__set_attach_target() and bpf_program__attach_kprobe()
>     to avoid duplicating BPF programs (Amery)
> v1: https://lore.kernel.org/all/20260507113915.24988-1-ihor.solodrai@linux.dev/
> 
> ---
>  .../selftests/bpf/prog_tests/vmlinux.c        | 45 ++++++++++++++++++-
>  .../selftests/bpf/progs/test_vmlinux.c        |  4 +-
>  2 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/vmlinux.c b/tools/testing/selftests/bpf/prog_tests/vmlinux.c
> index 6fb2217d940b..b5fdd593910d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/vmlinux.c
> +++ b/tools/testing/selftests/bpf/prog_tests/vmlinux.c
> @@ -14,21 +14,61 @@ static void nsleep()
>  	(void)syscall(__NR_nanosleep, &ts, NULL);
>  }
>  
> +static const char *hrtimer_func = "hrtimer_start_range_ns";
> +
> +static int setup_hrtimer_progs(struct test_vmlinux *skel)
> +{
> +	int err;
> +
> +	if (libbpf_find_vmlinux_btf_id("hrtimer_start_range_ns_user", BPF_TRACE_FENTRY) > 0)
> +		hrtimer_func = "hrtimer_start_range_ns_user";
> +
> +	err = bpf_program__set_attach_target(skel->progs.handle__fentry, 0, hrtimer_func);
> +	if (err)
> +		return err;
> +
> +	/*
> +	 * Bare SEC("kprobe") has no target function, so attach it manually
> +	 * later after selecting the hrtimer function to probe.
> +	 */
> +	bpf_program__set_autoattach(skel->progs.handle__kprobe, false);
> +
> +	return 0;
> +}
> +
>  void test_vmlinux(void)
>  {
>  	int err;
>  	struct test_vmlinux* skel;
>  	struct test_vmlinux__bss *bss;
> +	struct bpf_link *kprobe_link = NULL;
>  
> -	skel = test_vmlinux__open_and_load();
> -	if (!ASSERT_OK_PTR(skel, "test_vmlinux__open_and_load"))
> +	skel = test_vmlinux__open();
> +	if (!ASSERT_OK_PTR(skel, "test_vmlinux__open"))
>  		return;
> +
> +	err = setup_hrtimer_progs(skel);
> +	if (!ASSERT_OK(err, "setup_hrtimer_progs"))
> +		goto cleanup;
> +
> +	err = test_vmlinux__load(skel);
> +	if (!ASSERT_OK(err, "test_vmlinux__load"))
> +		goto cleanup;
> +
>  	bss = skel->bss;
>  
>  	err = test_vmlinux__attach(skel);
>  	if (!ASSERT_OK(err, "test_vmlinux__attach"))
>  		goto cleanup;
>  
> +	/* manually attach kprobe with the selected function */
> +	if (hrtimer_func) {
> +		kprobe_link = bpf_program__attach_kprobe(skel->progs.handle__kprobe,
> +							 false /* retprobe */, hrtimer_func);
> +		if (!ASSERT_OK_PTR(kprobe_link, "bpf_program__attach_kprobe"))
> +			goto cleanup;
> +	}
> +
>  	/* trigger everything */
>  	nsleep();
>  
> @@ -39,5 +79,6 @@ void test_vmlinux(void)
>  	ASSERT_TRUE(bss->fentry_called, "fentry");
>  
>  cleanup:
> +	bpf_link__destroy(kprobe_link);
>  	test_vmlinux__destroy(skel);
>  }
> diff --git a/tools/testing/selftests/bpf/progs/test_vmlinux.c b/tools/testing/selftests/bpf/progs/test_vmlinux.c
> index 78b23934d9f8..eea556940df6 100644
> --- a/tools/testing/selftests/bpf/progs/test_vmlinux.c
> +++ b/tools/testing/selftests/bpf/progs/test_vmlinux.c
> @@ -69,7 +69,7 @@ int BPF_PROG(handle__tp_btf, struct pt_regs *regs, long id)
>  	return 0;
>  }
>  
> -SEC("kprobe/hrtimer_start_range_ns")
> +SEC("kprobe")
>  int BPF_KPROBE(handle__kprobe, struct hrtimer *timer, ktime_t tim, u64 delta_ns,
>  	       const enum hrtimer_mode mode)
>  {
> @@ -78,7 +78,7 @@ int BPF_KPROBE(handle__kprobe, struct hrtimer *timer, ktime_t tim, u64 delta_ns,
>  	return 0;
>  }
>  
> -SEC("fentry/hrtimer_start_range_ns")
> +SEC("fentry")
>  int BPF_PROG(handle__fentry, struct hrtimer *timer, ktime_t tim, u64 delta_ns,
>  	     const enum hrtimer_mode mode)
>  {
> -- 
> 2.54.0
> 
>