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-rw-r--r--tools/lib/bpf/features.c32
1 files changed, 31 insertions, 1 deletions
diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index a336786a22..50befe125d 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -392,11 +392,41 @@ static int probe_uprobe_multi_link(int token_fd)
link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, &link_opts);
err = -errno; /* close() can clobber errno */
+ if (link_fd >= 0 || err != -EBADF) {
+ if (link_fd >= 0)
+ close(link_fd);
+ close(prog_fd);
+ return 0;
+ }
+
+ /* Initial multi-uprobe support in kernel didn't handle PID filtering
+ * correctly (it was doing thread filtering, not process filtering).
+ * So now we'll detect if PID filtering logic was fixed, and, if not,
+ * we'll pretend multi-uprobes are not supported, if not.
+ * Multi-uprobes are used in USDT attachment logic, and we need to be
+ * conservative here, because multi-uprobe selection happens early at
+ * load time, while the use of PID filtering is known late at
+ * attachment time, at which point it's too late to undo multi-uprobe
+ * selection.
+ *
+ * Creating uprobe with pid == -1 for (invalid) '/' binary will fail
+ * early with -EINVAL on kernels with fixed PID filtering logic;
+ * otherwise -ESRCH would be returned if passed correct binary path
+ * (but we'll just get -BADF, of course).
+ */
+ link_opts.uprobe_multi.pid = -1; /* invalid PID */
+ link_opts.uprobe_multi.path = "/"; /* invalid path */
+ link_opts.uprobe_multi.offsets = &offset;
+ link_opts.uprobe_multi.cnt = 1;
+
+ link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, &link_opts);
+ err = -errno; /* close() can clobber errno */
+
if (link_fd >= 0)
close(link_fd);
close(prog_fd);
- return link_fd < 0 && err == -EBADF;
+ return link_fd < 0 && err == -EINVAL;
}
static int probe_kern_bpf_cookie(int token_fd)