How to trace a program from its very beginning without running it as root

Question

I'm writing a tool that calls through to DTrace to trace the program that the user specifies.

If my tool uses dtrace -c to run the program as a subprocess of DTrace, not only can I not pass any arguments to the program, but the program runs with all the privileges of DTrace—that is, as root (I'm on Mac OS X). This makes certain things that should work break, and obviously makes a great many things that shouldn't work possible.

The other solution I know of is to start the program myself, pause it by sending it SIGSTOP, pass its PID to dtrace -p, then continue it by sending it SIGCONT. The problem is that either the program runs for a few seconds without being traced while DTrace gathers the symbol information or, if I sleep for a few seconds before continuing the process, DTrace complains that objc<pid>:<class>:<method>:entry matches no probes.

Is there a way that I can run the program under the user's account, not as root, but still have DTrace able to trace it from the beginning?

Answer 1

Create a launcher program that will wait for a signal of some sort (not necessarily a literal signal, just an indication that it's ready), then exec() your target. Now dtrace -p the launcher program, and once dtrace is up, let the launcher go.

Answer 2

If the other answer doesn't work for you, can you run the program in gdb, break in main (or even earlier), get the pid, and start the script? I've tried that in the past and it seemed to work.

Answer 3

Something like sudo dtruss -f sudo -u <original username> <command> has worked for me, but I felt bad about it afterwards.

I filed a Radar bug about it and had it closed as a duplicate of #5108629.