u* tools: Gracefully handle missing probes
When the target process is missing the required USDT probes, it can
be a simple mistake (e.g. attaching a script as Java to a Python
process), or a runtime that is not instrumented with the required
probes. Attempt to gracefully handle the error and print a helpful
message instructing the user why the error might have occurred.
```
$ uthreads -l java $(pidof python)
Error attaching USDT probes: the specified pid might not contain
the given language's runtime, or the runtime was not built with the
required USDT probes. Look for a configure flag similar to
--with-dtrace or --enable-dtrace. To check which probes are present
in the process, use the tplist tool.
```
diff --git a/tools/ucalls.py b/tools/ucalls.py
index 90b2d47..7cdf390 100755
--- a/tools/ucalls.py
+++ b/tools/ucalls.py
@@ -219,9 +219,9 @@
if args.language:
usdt = USDT(pid=args.pid)
- usdt.enable_probe(entry_probe, "trace_entry")
+ usdt.enable_probe_or_bail(entry_probe, "trace_entry")
if args.latency:
- usdt.enable_probe(return_probe, "trace_return")
+ usdt.enable_probe_or_bail(return_probe, "trace_return")
else:
usdt = None