netdev - [PATCH 6/7] libbpf: allow specification of "kprobe/function+offset"

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Date:   Wed,  7 Jul 2021 21:46:18 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Alan Maguire <alan.maguire@...cle.com>
Subject: [PATCH 6/7] libbpf: allow specification of "kprobe/function+offset"

From: Alan Maguire <alan.maguire@...cle.com>

kprobes can be placed on most instructions in a function, not
just entry, and ftrace and bpftrace support the function+offset
notification for probe placement.  Adding parsing of func_name
into func+offset to bpf_program__attach_kprobe() allows the
user to specify

SEC("kprobe/bpf_fentry_test5+0x6")

...for example, and the offset can be passed to perf_event_open_probe()
to support kprobe attachment.

Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/lib/bpf/libbpf.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 1e04ce724240..60c9e3e77684 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10309,11 +10309,25 @@ struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
 					    const char *func_name)
 {
 	char errmsg[STRERR_BUFSIZE];
+	char func[BPF_OBJ_NAME_LEN];
+	unsigned long offset = 0;
 	struct bpf_link *link;
-	int pfd, err;
+	int pfd, err, n;
+
+	n = sscanf(func_name, "%[a-zA-Z0-9_.]+%lx", func, &offset);
+	if (n < 1) {
+		err = -EINVAL;
+		pr_warn("kprobe name is invalid: %s\n", func_name);
+		return libbpf_err_ptr(err);
+	}
+	if (retprobe && offset != 0) {
+		err = -EINVAL;
+		pr_warn("kretprobes do not support offset specification\n");
+		return libbpf_err_ptr(err);
+	}
 
-	pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
-				    0 /* offset */, -1 /* pid */);
+	pfd = perf_event_open_probe(false /* uprobe */, retprobe, func,
+				    offset, -1 /* pid */);
 	if (pfd < 0) {
 		pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
 			prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
-- 
2.31.1