[lldb-dev] Debugging a running process with lldb

Matthew Gardiner mg11 at csr.com
Wed May 14 02:09:56 PDT 2014

Hi folks

On reading the documentation for lldb am I correct in understanding that 
for a running inferior program being debugged by lldb, that the input 
reader, i.e. the (lldb) prompt should be active at all times?

For instance, from "http://lldb.llvm.org/tutorial.html":

"The commands that currently work while running include interrupting the 
process to halt execution ("process interrupt"), getting the process 
status ("process status"), breakpoint setting and clearing (" breakpoint 
[set|clear|enable|disable|list] ..."), and memory reading and writing (" 
memory [read|write] ...")."

I interpret this to mean whenever debugging a program regardless of the 
run/stop state of any of it's threads, lldb must always print:


after processing the last command, since we require an active prompt in 
order to process the issuing of the above commands (from the lldb user) 
when the inferior is running.

In that case I have found a bug on my 64-bit linux build. I firstly 
launch lldb to debug a simple inferior (64-bit linux process), stop it 
on entry, then resume it. The (lldb) prompt does not reappear after I 
have resumed:

$ lldb ./forever
Traceback (most recent call last):
   File "<string>", line 1, in <module>
ImportError: No module named lldb.embedded_interpreter
Current executable set to './forever' (x86_64).
(lldb) process launch -s
Process 1901 launching
Process 1901 launched: './forever' (x86_64)
Process 1901 stopped
* thread #1: tid = 1901, 0x0000003675a011f0, name = 'forever', stop 
reason = trace
     frame #0: 0x0000003675a011f0
-> 0x3675a011f0:  movq   %rsp, %rdi
    0x3675a011f3:  callq  0x3675a046e0
    0x3675a011f8:  movq   %rax, %r12
    0x3675a011fb:  movl   0x21eb97(%rip), %eax
(lldb) process continue
Process 1901 resuming

Are other people seeing this bug?

thank you
Matthew Gardiner

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