On Fri, Oct 18, 2019 at 07:54:26AM -0700, John Fastabend wrote:
> Following ./Documentation/trace/kprobetrace.rst add support for loading
> kprobes programs on older kernels.
>
> Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 81 +++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 73 insertions(+), 8 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fcea6988f962..12b3105d112c 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -5005,20 +5005,89 @@ static int determine_uprobe_retprobe_bit(void)
> return parse_uint_from_file(file, "config:%d\n");
> }
>
> +static int use_kprobe_debugfs(const char *name,
> + uint64_t offset, int pid, bool retprobe)
offset & pid unused?
> +{
> + const char *file = "/sys/kernel/debug/tracing/kprobe_events";
> + int fd = open(file, O_WRONLY | O_APPEND, 0);
> + char buf[PATH_MAX];
> + int err;
> +
> + if (fd < 0) {
> + pr_warning("failed open kprobe_events: %s\n",
> + strerror(errno));
> + return -errno;
> + }
> +
> + snprintf(buf, sizeof(buf), "%c:kprobes/%s %s",
> + retprobe ? 'r' : 'p', name, name);
> +
> + err = write(fd, buf, strlen(buf));
> + close(fd);
> + if (err < 0)
> + return -errno;
> + return 0;
> +}
> +
> 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];
> + uint64_t config1 = 0;
> 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 (uprobe) {
> + pr_warning("failed to determine uprobe perf type %s: %s\n",
> + name,
> + libbpf_strerror_r(type,
> + errmsg, sizeof(errmsg)));
> + } else {
> + /* If we do not have an event_source/../kprobes then we
> + * can try to use kprobe-base event tracing, for details
> + * see ./Documentation/trace/kprobetrace.rst
> + */
> + const char *file = "/sys/kernel/debug/tracing/events/kprobes/";
> + char c[PATH_MAX];
> + int fd, n;
> +
> + snprintf(c, sizeof(c), "%s/%s/id", file, name);
> +
> + err = use_kprobe_debugfs(name, offset, pid, retprobe);
> + if (err)
> + return err;
Should we throw a pr_warning() here as well when bailing out?
> + type = PERF_TYPE_TRACEPOINT;
> + fd = open(c, O_RDONLY, 0);
> + if (fd < 0) {
> + pr_warning("failed to open tracepoint %s: %s\n",
> + c, strerror(errno));
> + return -errno;
> + }
> + n = read(fd, c, sizeof(c));
> + close(fd);
> + if (n < 0) {
> + pr_warning("failed to read %s: %s\n",
> + c, strerror(errno));
> + return -errno;
> + }
> + c[n] = '\0';
> + config1 = strtol(c, NULL, 0);
> + attr.size = sizeof(attr);
> + attr.type = type;
> + attr.config = config1;
> + attr.sample_period = 1;
> + attr.wakeup_events = 1;
Is there a reason you set latter two whereas below they are not set,
does it not default to these?
> + }
> + } else {
> + config1 = ptr_to_u64(name);
> + attr.size = sizeof(attr);
> + attr.type = type;
> + attr.config1 = config1; /* kprobe_func or uprobe_path */
> + attr.config2 = offset; /* kprobe_addr or probe_offset */
> }
> if (retprobe) {
> int bit = uprobe ? determine_uprobe_retprobe_bit()
> @@ -5033,10 +5102,6 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
> }
> attr.config |= 1 << bit;
> }
What happens in case of retprobe, don't you (unwantedly) bail out here
again (even through you've set up the retprobe earlier)?
> - attr.size = sizeof(attr);
> - attr.type = type;
> - attr.config1 = ptr_to_u64(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,
>
