linux-kernel - [RFC PATCH] libbpf: Add bpf_program__set_section

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Date: Mon, 25 Mar 2024 23:47:37 +0800
From: Tao Chen <chen.dylane@...il.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	chen.dylane@...il.com
Subject: [RFC PATCH] libbpf: Add bpf_program__set_section_name api

The new api can be used to reset the function we want to trace in
runtime. So we need not to change the code again when we just do
minor changes to the trace function in kprobe or other ebpf event
type. We can replace the old section with new section passed in via
parameter. Maybe the following scenario we can use the api:

1. solve "*.isra.o" issue caused by compiler in new kernel
obj = offcputime_bpf__open();
bpf_program__set_section_name(*(obj->skeleton->obj),
"kprobe/finish_task_switch", "kprobe/finish_task_switch.isra.0");

2. dynamic adjustment for trace function offset
obj = offcputime_bpf__open();
bpf_program__set_section_name(*(obj->skeleton->obj),
"kprobe/finish_task_switch+23", "kprobe/finish_task_switch+45");

Signed-off-by: Tao Chen <chen.dylane@...il.com>
---
 tools/lib/bpf/libbpf.c   | 24 ++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  2 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 27 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 96ff1aa4bf6a..94f32e845c61 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8576,6 +8576,30 @@ const char *bpf_program__section_name(const struct bpf_program *prog)
 	return prog->sec_name;
 }
 
+int bpf_program__set_section_name(struct bpf_object *obj, const char *old_sec,
+				  const char *new_sec)
+{
+	struct bpf_program *prog = NULL;
+
+	if (obj == NULL || old_sec == NULL || new_sec == NULL)
+		return libbpf_err(-EINVAL);
+
+	do {
+		prog = bpf_object__next_program(obj, NULL);
+		if (prog) {
+			if (strcmp(prog->sec_name, old_sec) == 0) {
+				free(prog->sec_name);
+				prog->sec_name = strdup(new_sec);
+				if (!prog->sec_name)
+					return libbpf_err(-ENOMEM);
+				return 0;
+			}
+		}
+	} while (prog);
+
+	return libbpf_err(-ENOENT);
+}
+
 bool bpf_program__autoload(const struct bpf_program *prog)
 {
 	return prog->autoload;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 0e52621cba43..eb620a9c8b8a 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -307,6 +307,8 @@ LIBBPF_API void bpf_program__set_ifindex(struct bpf_program *prog,
 
 LIBBPF_API const char *bpf_program__name(const struct bpf_program *prog);
 LIBBPF_API const char *bpf_program__section_name(const struct bpf_program *prog);
+LIBBPF_API int bpf_program__set_section_name(struct bpf_object *obj, const char *old_sec,
+					     const char *new_sec);
 LIBBPF_API bool bpf_program__autoload(const struct bpf_program *prog);
 LIBBPF_API int bpf_program__set_autoload(struct bpf_program *prog, bool autoload);
 LIBBPF_API bool bpf_program__autoattach(const struct bpf_program *prog);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 57712321490f..14ac62cff605 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -400,4 +400,5 @@ LIBBPF_1.3.0 {
 		bpf_program__attach_netfilter;
 		bpf_program__attach_tcx;
 		bpf_program__attach_uprobe_multi;
+		bpf_program__set_section_name;
 } LIBBPF_1.2.0;
-- 
2.34.1