[lldb-dev] Debugging a running process with lldb

jingham at apple.com jingham at apple.com
Wed May 14 10:56:03 PDT 2014

Note that on OS X with the current TOT lldb, "process launch --no-stdin" works as advertised.


On May 14, 2014, at 10:17 AM, Greg Clayton <gclayton at apple.com> wrote:

> If we launch a process and hookup a pty to its stdin/out/err, then we shouldn't get a 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.
>> On May 14, 2014, at 3:22 AM, Matthew Gardiner <mg11 at csr.com> wrote:
>> More thoughts:
>> I've read http://lldb.llvm.org/tutorial.html in more depth now ;-) (appreciating that the debugger and the inferior require separate stdins.)
>> I see there's an option, "--no-stdin", proposing to mitigate the issue I found
>> "If you attach to a process, or launch a process with the "|--no-stdin|" option, the command interpreter is always available to enter commands. This might be a little disconcerting to gdb users when always have an |(lldb)| prompt. This allows you to set a breakpoint, etc without having to explicitly interrupt the program you are debugging:
>> |(lldb) process continue
>> (lldb) breakpoint set --name stop_here |
>> "
>> However, it seems that --no-stdin is not present as a "process launch" option anymore, but rather we have "--no-stdio". (Perhaps a typo, somewhere?). I tried this option:
>> (lldb) process launch -s --no-stdio
>> Process 2344 launching
>> Process 2344 launched: './forever' (x86_64)
>> Process 2344 stopped
>> * thread #1: tid = 2344, 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 2344 resuming
>> The interpreter prompt still fails to appear, so I still think I'm either seeing a bug, or that the documentation is incomplete as to describing how to run lldb such that the command interpreter, is always available when the inferior is running.
>> thanks
>> Matt
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