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libbpf: Allow specification of "kprobe/function+offset"

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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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210714094400.396467-8-jolsa@kernel.org
This commit is contained in:
Alan Maguire 2021-07-14 11:43:59 +02:00 committed by Alexei Starovoitov
parent ac0ed48829
commit a2488b5f48
1 changed files with 22 additions and 2 deletions
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24
tools/lib/bpf/libbpf.c
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@ -10348,6 +10348,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
struct bpf_program_attach_kprobe_opts {
bool retprobe;
unsigned long offset;
};
static struct bpf_link*
@ -10360,7 +10361,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
int pfd, err;
pfd = perf_event_open_probe(false /* uprobe */, opts->retprobe, func_name,
0 /* offset */, -1 /* pid */);
opts->offset, -1 /* pid */);
if (pfd < 0) {
pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
prog->name, opts->retprobe ? "kretprobe" : "kprobe", func_name,
@ -10394,12 +10395,31 @@ static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
struct bpf_program *prog)
{
struct bpf_program_attach_kprobe_opts opts;
unsigned long offset = 0;
struct bpf_link *link;
const char *func_name;
char *func;
int n, err;
func_name = prog->sec_name + sec->len;
opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;
return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
n = sscanf(func_name, "%m[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 (opts.retprobe && offset != 0) {
err = -EINVAL;
pr_warn("kretprobes do not support offset specification\n");
return libbpf_err_ptr(err);
}
opts.offset = offset;
link = bpf_program__attach_kprobe_opts(prog, func, &opts);
free(func);
return link;
}
struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,