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Date: Mon, 1 Jul 2019 15:08:24 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Yonghong Song <yhs@...com>
Cc: Andrii Nakryiko <andriin@...com>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
"daniel@...earbox.net" <daniel@...earbox.net>,
Kernel Team <Kernel-team@...com>,
"sdf@...ichev.me" <sdf@...ichev.me>,
Song Liu <songliubraving@...com>
Subject: Re: [PATCH v4 bpf-next 4/9] libbpf: add kprobe/uprobe attach API
On Mon, Jul 1, 2019 at 10:09 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 6/28/19 8:49 PM, Andrii Nakryiko wrote:
> > Add ability to attach to kernel and user probes and retprobes.
> > Implementation depends on perf event support for kprobes/uprobes.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> > tools/lib/bpf/libbpf.c | 165 +++++++++++++++++++++++++++++++++++++++
> > tools/lib/bpf/libbpf.h | 7 ++
> > tools/lib/bpf/libbpf.map | 2 +
> > 3 files changed, 174 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 98c155ec3bfa..2f79e9563db9 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -4019,6 +4019,171 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
> > return (struct bpf_link *)link;
> > }
> >
> > +static int parse_value_from_file(const char *file, const char *fmt)
>
> Here, the value from the file must be positive int values to avoid
> confusion between valid value vs. error code.
> Could you add a comment to state this fact for the current
> uprobe/kprobe/tracepoint support?
You are right. I'll name it parse_uint_from_file to make it more
obvious (though even that is not strictly true, we expect value in the
range of [0, 2^32-1]. I'll leave a comment.
>
> > +{
> > + char buf[STRERR_BUFSIZE];
> > + int err, ret;
> > + FILE *f;
> > +
> > + f = fopen(file, "r");
> > + if (!f) {
> > + err = -errno;
> > + pr_debug("failed to open '%s': %s\n", file,
> > + libbpf_strerror_r(err, buf, sizeof(buf)));
> > + fclose(f);
>
> fclose(f) is not needed. fopen has failed.
*facepalm*, of course, thanks!
>
> > + return err;
> > + }
> > + err = fscanf(f, fmt, &ret);
> > + if (err != 1) {
> > + err = err == EOF ? -EIO : -errno;
> > + pr_debug("failed to parse '%s': %s\n", file,
> > + libbpf_strerror_r(err, buf, sizeof(buf)));
> > + fclose(f);
> > + return err;
> > + }
> > + fclose(f);
> > + return ret;
> > +}
> > +
> > +static int determine_kprobe_perf_type(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/kprobe/type";
> > +
> > + return parse_value_from_file(file, "%d\n");
> > +}
> > +
> > +static int determine_uprobe_perf_type(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/uprobe/type";
> > +
> > + return parse_value_from_file(file, "%d\n");
> > +}
> > +
> > +static int determine_kprobe_retprobe_bit(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/kprobe/format/retprobe";
> > +
> > + return parse_value_from_file(file, "config:%d\n");
> > +}
> > +
> > +static int determine_uprobe_retprobe_bit(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
> > +
> > + return parse_value_from_file(file, "config:%d\n");
> > +}
> > +
> > +static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
> > + uint64_t offset, int pid)
> > +{
> > + struct perf_event_attr attr = {};
> > + char errmsg[STRERR_BUFSIZE];
> > + int type, pfd, err;
> > +
> > + type = uprobe ? determine_uprobe_perf_type()
> > + : determine_kprobe_perf_type();
> > + if (type < 0) {
> > + pr_warning("failed to determine %s perf type: %s\n",
> > + uprobe ? "uprobe" : "kprobe",
> > + libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
> > + return type;
> > + }
> > + if (retprobe) {
> > + int bit = uprobe ? determine_uprobe_retprobe_bit()
> > + : determine_kprobe_retprobe_bit();
> > +
> > + if (bit < 0) {
> > + pr_warning("failed to determine %s retprobe bit: %s\n",
> > + uprobe ? "uprobe" : "kprobe",
> > + libbpf_strerror_r(bit, errmsg,
> > + sizeof(errmsg)));
> > + return bit;
> > + }
> > + attr.config |= 1 << bit;
> > + }
> > + attr.size = sizeof(attr);
> > + attr.type = type;
> > + attr.config1 = (uint64_t)(void *)name; /* kprobe_func or uprobe_path */
> > + attr.config2 = offset; /* kprobe_addr or probe_offset */
> > +
> > + /* pid filter is meaningful only for uprobes */
> > + pfd = syscall(__NR_perf_event_open, &attr,
> > + pid < 0 ? -1 : pid /* pid */,
> > + pid == -1 ? 0 : -1 /* cpu */,
> > + -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
> > + if (pfd < 0) {
> > + err = -errno;
> > + pr_warning("%s perf_event_open() failed: %s\n",
> > + uprobe ? "uprobe" : "kprobe",
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + return err;
> > + }
> > + return pfd;
> > +}
> > +
> > +struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
> > + bool retprobe,
> > + const char *func_name)
> > +{
> > + char errmsg[STRERR_BUFSIZE];
> > + struct bpf_link *link;
> > + int pfd, err;
> > +
> > + pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
> > + 0 /* offset */, -1 /* pid */);
> > + if (pfd < 0) {
> > + pr_warning("program '%s': failed to create %s '%s' perf event: %s\n",
> > + bpf_program__title(prog, false),
> > + retprobe ? "kretprobe" : "kprobe", func_name,
> > + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> > + return ERR_PTR(pfd);
> > + }
> > + link = bpf_program__attach_perf_event(prog, pfd);
> > + if (IS_ERR(link)) {
> > + close(pfd);
> > + err = PTR_ERR(link);
> > + pr_warning("program '%s': failed to attach to %s '%s': %s\n",
> > + bpf_program__title(prog, false),
> > + retprobe ? "kretprobe" : "kprobe", func_name,
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + return link;
> > + }
> > + return link;
> > +}
> > +
> > +struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,
> > + bool retprobe, pid_t pid,
> > + const char *binary_path,
> > + size_t func_offset)
> > +{
> > + char errmsg[STRERR_BUFSIZE];
> > + struct bpf_link *link;
> > + int pfd, err;
> > +
> > + pfd = perf_event_open_probe(true /* uprobe */, retprobe,
> > + binary_path, func_offset, pid);
> > + if (pfd < 0) {
> > + pr_warning("program '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
> > + bpf_program__title(prog, false),
> > + retprobe ? "uretprobe" : "uprobe",
> > + binary_path, func_offset,
> > + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> > + return ERR_PTR(pfd);
> > + }
> > + link = bpf_program__attach_perf_event(prog, pfd);
> > + if (IS_ERR(link)) {
> > + close(pfd);
> > + err = PTR_ERR(link);
> > + pr_warning("program '%s': failed to attach to %s '%s:0x%zx': %s\n",
> > + bpf_program__title(prog, false),
> > + retprobe ? "uretprobe" : "uprobe",
> > + binary_path, func_offset,
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + return link;
> > + }
> > + return link;
> > +}
> > +
> > enum bpf_perf_event_ret
> > bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
> > void **copy_mem, size_t *copy_size,
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index 1bf66c4a9330..bd767cc11967 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -171,6 +171,13 @@ LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
> >
> > LIBBPF_API struct bpf_link *
> > bpf_program__attach_perf_event(struct bpf_program *prog, int pfd);
> > +LIBBPF_API struct bpf_link *
> > +bpf_program__attach_kprobe(struct bpf_program *prog, bool retprobe,
> > + const char *func_name);
> > +LIBBPF_API struct bpf_link *
> > +bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
> > + pid_t pid, const char *binary_path,
> > + size_t func_offset);
> >
> > struct bpf_insn;
> >
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 756f5aa802e9..57a40fb60718 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -169,7 +169,9 @@ LIBBPF_0.0.4 {
> > global:
> > bpf_link__destroy;
> > bpf_object__load_xattr;
> > + bpf_program__attach_kprobe;
> > bpf_program__attach_perf_event;
> > + bpf_program__attach_uprobe;
> > btf_dump__dump_type;
> > btf_dump__free;
> > btf_dump__new;
> >
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