[lldb-dev] Debugging a running process with lldb

Matthew Gardiner mg11 at csr.com
Thu May 15 01:53:19 PDT 2014

Matthew Gardiner wrote:
> Greg Clayton wrote:
>> If we launch a process and hookup a pty to its stdin/out/err, then we 
>> shouldn't get a prompt.
> Sorry, I don't understand this. Surely if we attach the inferior's 
> (i.e. what you termed the process) standard IOs to a pty, then we 
> *will* get a prompt, since then lldb can use it's terminal with no 
> corruption from the inferiors in/out?
> (I'm not actually clear about the relationship between the "process 
> launch" -t and -n commands. I do accept that they are mutually 
> exclusive. I assume, -n means that the stdin/out/err of the inferior 
> is closed, so that lldb has complete use of the foreground, so it 
> could use it's prompt. I assume -t means attach the inferior to a 
> different pty, so again, lldb should still be able to use it's prompt.)
>>   It is probably a bug where if you launch with --no-stdio that the 
>> LLDB prompt isn't always active.
>> For attach, we will always have a prompt.
>> So seems this is a bug that --no-stdio is still pushing a Process 
>> IOHandler and taking over the console while the process is running.
> So you are saying if I do
> (lldb) process launch -s --no-stdio
> then
> (lldb) process continue
> then I should always see:
> (lldb)
> back on my terminal?
> Todd, could you try this (a couple of times, in case I'm seeing 
> something intermittent) please, to see if your observations agree?
> thanks
> Matt
Hi Greg,

Actually, my colleague just brought his MacBook (OSX 10.9.2) into work, 
this morning. He installed pre-built xcode/lldb (lldb-310.2.37) on his 
Mac, and I can confirm that on mac, when we invoked:

(lldb) process launch -s -n
Process 1002 lanched....
(lldb) process continue
Process 1002 resuming

then we see the interpreter prompt return after the "continue". So what 
I reported originally is a linux build bug. (Perhaps I'll start digging 
into this, if I get any time...).

However, using  "process launch -s -t" on the mac, was buggy, a 
terminal-emulator was spawned, but (presumably) lldb and the child 
terminal fail to synchronise using the UNIX socket.

(lldb) process launch -s -t
error: failed to launch or debug process

Anyway, sorry for my earlier rant ;-), but at least now I'm a little 
clearer about the intended semantics...


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