Attach lldb/gdb to a short-lived process?

Question

I am debugging a program that is short-lived. That is, it won't stop and wait for the lldb/gdb debugger to attach. So how can I attach lldb debugger to this kind of process?

Get the debugger to start the process? Change the code to add a sleep at the start? — Ed Heal
– Ed Heal, Commented Dec 21, 2014 at 8:44
Have some way to test that program independently, and start it inside gdb — Basile Starynkevitch
– Basile Starynkevitch, Commented Dec 21, 2014 at 8:45
@EdHeal I am using vim-lldb as a lldb frontend, so it is not possible to start it in the debugger. And I don't think hacking into the code is a good idea :) — John Wu
– John Wu, Commented Dec 21, 2014 at 8:52
One would imagine that you have access to the source code (hence doing the debugging). Just put after main a sleep for ten seconds . Give you time to attach the debugger — Ed Heal
– Ed Heal, Commented Dec 21, 2014 at 8:55

Jason Molenda · Accepted Answer · 2014-12-21 20:31:04Z

1

The traditional approach is to have a sleep loop, or if you have access to the source, to put a busyloop like

int wait_for_debugger = 1
while (wait_for_debugger)
    ;

Then you attach to the process and set wait_for_debugger to 0 (e.g. p wait_for_debugger = 0) and continue the process.

lldb has a --waitfor option to attach to a process. This has lldb repeatedly poll the process table looking for a new instance of that process name and attaches to it. The process will get to execute a little bit but the polling frequency is high enough that it usually catches things early enough. This is the process launch --waitfor --name procname command, or pr la -w -n processname for short.

answered Dec 21, 2014 at 20:31

Jason Molenda

15.6k1 gold badge64 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jww · Accepted Answer · 2014-12-21 09:31:38Z

1

So how can I attach lldb debugger to this kind of process?

Attach the debugger to the parent process, and set follow-fork-mode child. According to the docs, "The new process is debugged after a fork. The parent process runs unimpeded". See 4.11 Debugging Forks in the GDB manual.

answered Dec 21, 2014 at 9:31

jww

104k107 gold badges453 silver badges975 bronze badges

Collectives™ on Stack Overflow

Attach lldb/gdb to a short-lived process?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related