Re: [RFC PATCH bpf-next 1/1] libbpf: Auto-upgrade uprobes to multi-uprobes when supported

[Yonghong Song]

On 2/12/26 7:20 AM, Varun R Mallya wrote:
> This patch modifies libbpf to automatically "upgrade" standard
> SEC("uprobe") and SEC("uretprobe") programs to use the multi-uprobe
> infrastructure (BPF_TRACE_UPROBE_MULTI) at load time if the kernel
> supports it, making them compatible with BPF tokens.
>
> To maintain backward compatibility and handle rare cases where singular
> uprobes are required, new SEC("uprobe.single") and SEC("uretprobe.single")
> section types are introduced. These force libbpf to use the legacy
> perf_event_open() attachment path.

Maybe you can have bpf programs for both uprobe/uretprobe
and uprobe.multi/uretprobe.multi?

You can add "?" before the section name (e.g., SEC("?uprobe") so you can
selectively enable those programs before loading. This one if one choice
e.g. uprobe/uretprobe is not working, you can then try
uprobe.multi/uretprobe.multi.

> Signed-off-by: Varun R Mallya <varunrmallya@xxxxxxxxx>
> ---
>   tools/lib/bpf/libbpf.c | 42 ++++++++++++++++++++++++++++++++++++------
>   1 file changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0c8bf0b5cce4..a32f221d3245 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8265,6 +8265,22 @@ static int bpf_object_init_progs(struct bpf_object *obj, const struct bpf_object
>   		prog->type = prog->sec_def->prog_type;
>   		prog->expected_attach_type = prog->sec_def->expected_attach_type;
>   
> +		/* set BPF_TRACE_UPROBE_MULTI if sec_name matches "u[ret]probe"
> +		 * otherwise, leave alone.
> +		 */
> +		if (kernel_supports(obj, FEAT_UPROBE_MULTI_LINK)) {
> +			char *probe_type = NULL;
> +			int n;
> +
> +			n = sscanf(prog->sec_name, "%m[^/]", &probe_type);
> +			if (n >= 1)
> +				if (!strcmp(probe_type, "uprobe") ||
> +				    !strcmp(probe_type, "uretprobe"))
> +					prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> +
> +			free(probe_type);
> +		}
> +
>   		/* sec_def can have custom callback which should be called
>   		 * after bpf_program is initialized to adjust its properties
>   		 */
> @@ -9822,9 +9838,11 @@ static const struct bpf_sec_def section_defs[] = {
>   	SEC_DEF("kprobe+",		KPROBE,	0, SEC_NONE, attach_kprobe),
>   	SEC_DEF("uprobe+",		KPROBE,	0, SEC_NONE, attach_uprobe),
>   	SEC_DEF("uprobe.s+",		KPROBE,	0, SEC_SLEEPABLE, attach_uprobe),
> +	SEC_DEF("uprobe.single+",	KPROBE,	0, SEC_NONE, attach_uprobe),
>   	SEC_DEF("kretprobe+",		KPROBE, 0, SEC_NONE, attach_kprobe),
>   	SEC_DEF("uretprobe+",		KPROBE, 0, SEC_NONE, attach_uprobe),
>   	SEC_DEF("uretprobe.s+",		KPROBE, 0, SEC_SLEEPABLE, attach_uprobe),
> +	SEC_DEF("uretprobe.single+",	KPROBE,	0, SEC_NONE, attach_uprobe),
>   	SEC_DEF("kprobe.multi+",	KPROBE,	BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
>   	SEC_DEF("kretprobe.multi+",	KPROBE,	BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
>   	SEC_DEF("kprobe.session+",	KPROBE,	BPF_TRACE_KPROBE_SESSION, SEC_NONE, attach_kprobe_session),
> @@ -12722,10 +12740,10 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
>    */
>   static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
>   {
> -	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
>   	char *probe_type = NULL, *binary_path = NULL, *func_name = NULL, *func_off;
>   	int n, c, ret = -EINVAL;
>   	long offset = 0;
> +	bool is_retprobe;
>   
>   	*link = NULL;
>   
> @@ -12752,15 +12770,27 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
>   			else
>   				offset = 0;
>   		}
> -		opts.retprobe = strcmp(probe_type, "uretprobe") == 0 ||
> -				strcmp(probe_type, "uretprobe.s") == 0;
> -		if (opts.retprobe && offset != 0) {
> +		is_retprobe = strcmp(probe_type, "uretprobe") == 0 ||
> +			      strcmp(probe_type, "uretprobe.s") == 0;
> +		if (is_retprobe && offset != 0) {
>   			pr_warn("prog '%s': uretprobes do not support offset specification\n",
>   				prog->name);
>   			break;
>   		}
> -		opts.func_name = func_name;
> -		*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
> +		if (prog->expected_attach_type == BPF_TRACE_UPROBE_MULTI) {
> +			DECLARE_LIBBPF_OPTS(bpf_uprobe_multi_opts, opts);
> +
> +			opts.retprobe = is_retprobe;
> +			*link = bpf_program__attach_uprobe_multi(prog, -1, binary_path,
> +								 func_name, &opts);
> +		} else {
> +			DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
> +
> +			opts.retprobe = is_retprobe;
> +			opts.func_name = func_name;
> +			*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path,
> +								offset, &opts);
> +		}
>   		ret = libbpf_get_error(*link);
>   		break;
>   	default: