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

Jiri Olsa
2021-07-07T19:47:12Z

From: Alan Maguire <alan.maguire@oracle.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@oracle.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.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