Re: [PATCHv3 bpf-next 6/7] libbpf: allow specification of "kprobe/function+offset"
From: Andrii Nakryiko <hidden>
Date: 2021-07-08 00:14:34
Also in:
bpf
On Wed, Jul 7, 2021 at 2:54 PM Jiri Olsa [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Alan Maguire <redacted> 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 <redacted> 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)
I think we should add bpf_program__attach_kprobe_opts instead for the programmatic API instead of parsing it here from func_name. It's a cumbersome API. Parsing SEC() is fine, of course, but then it has to call into bpf_program__attach_kprobe_opts() internally.
{
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