[lldb-dev] LLDB Process Attach Failed When Waiting

Ryan Lovelett via lldb-dev lldb-dev at lists.llvm.org
Tue Jun 5 17:44:43 PDT 2018

I think I might be a little lost. I built a lldb in debug mode and I am
running lldb in an lldb debugger (very meta).
Earlier in the thread you said "we need a better error message when
vAttachWait returns unsupported" I have found where the error message,
e.g., "error: attach failed: lost connection" is constructed. The
"attach failed: " comes from here [1] and the "lost connection" comes
from here [2].
What do you mean by "vAttachWait"? Am I missing something obvious?

It seems like you are expecting lldb-server to be the place where the
fix will be implemented. Though in the debugger I'm seeing the method
Target::Attach() [3] as the place where the connection attempt is made
and fails.
[1] https://github.com/apple/swift-lldb/blob/a8c149f75a8cba674bead048cd9c80ddc8166a8a/source/Commands/CommandObjectProcess.cpp#L518[2] https://github.com/apple/swift-lldb/blob/a8c149f75a8cba674bead048cd9c80ddc8166a8a/source/Target/Target.cpp#L3444-L3445[3] https://github.com/apple/swift-lldb/blob/a8c149f75a8cba674bead048cd9c80ddc8166a8a/source/Target/Target.cpp#L3374
On Mon, Jun 4, 2018, at 7:04 PM, Greg Clayton wrote:
> I will be too busy this week to get to this, so please do have a
> stab at it.> 
> Basically the flow that debug server does is:
> 1 - get a list of all processes whose basename matches and remember
> those pids so we don't try to attach to them since we are waiting for
> a new process to show up> 2 - poll the OS for the process list and wait for a new pid to show up
> with the basename and attach to the first one that matches whose pid
> isn't i the list from step #1> 
> On MacOSX we don't have a way to be notified of new processes are
> spawned, not sure on other unix variants. If it is possible, we would
> want change to:> 1 - sign up to be notified about new processes
> 2 - as each process gets launched, check for a match and attach as
> quickly as possible> 
> Hope this helps and I look forward to seeing your patch!
> Greg
>> On Jun 4, 2018, at 5:56 AM, Ryan Lovelett <ryan at lovelett.me> wrote:
>> Greg,
>> Is there anything I can do to help you implement or test this
>> feature? Obviously I'm willing to roll-up my sleeves and work on this
>> myself too if you've become more busy than you expected. That happens
>> to us all and I completely understand.>> 
>> Not being able to debug in this manner is blocking me from adding
>> Linux support to a Swift program. As you might imagine, I'm a little
>> antsy to get past this so I can start writing some code.>> 
>> On Thu, May 31, 2018, at 5:08 PM, Greg Clayton wrote:
>>>> On May 31, 2018, at 12:40 PM, Ryan Lovelett <ryan at lovelett.me>
>>>> wrote:>>>> 
>>>> Well at least there is a little good news. I understood way more of
>>>> those logs than I thought I did.>>>> 
>>>>> So two issues here:
>>>>> 1 - we need a better error message when vAttachWait returns
>>>>> unsupported>>>>> 2 - fix lldb-server to support vAttachWait
>>>> A few questions.
>>>> What is the protocol here? Can/should I report the issues at
>>>> https://bugs.llvm.org/ ? Or is that something that a project member
>>>> needs to do? Assuming that I can, would this be two seperate issues
>>>> or one "large" issue?>>>> 
>>>> Barring that this is not something someone else might implement
>>>> better/faster than me. Considering I have zero LLDB development
>>>> experience is this something that I could tackle?>>> 
>>> I didn't realize this functionality was missing in lldb-server. I
>>> can take a stab at implementing it and see what I can do. Stay
>>> tuned.>>> 
>>>> On Thu, May 31, 2018, at 3:02 PM, Greg Clayton wrote:
>>>>> lldb-server claims it doesn't support it:
>>>>> lldb             <  48> send packet:
>>>>> $vAttachWait;6c616e677365727665722d7377696674#d6>>>>> lldb             <   4> read packet: $#00
>>>>> Returning the empty packet ("$#00") means it is not supported, but
>>>>> we really should give a better error message than this.>>>>> 
>>>>> It isn't that hard to implement. It would be easy to copy the code
>>>>> that is in debugserver in DNB.cpp in the DNBProcessAttachWait
>>>>> function. Most of it is probably posix style stuff.>>>>> 
>>>>> So two issues here:
>>>>> 1 - we need a better error message when vAttachWait returns
>>>>> unsupported>>>>> 2 - fix lldb-server to support vAttachWait
>>>>> Greg
>>>>>> On May 31, 2018, at 11:04 AM, Ryan Lovelett <ryan at lovelett.me>
>>>>>> wrote:>>>>>> 
>>>>>>> It might be a lldb-server issue?
>>>>>> How would one go about determining this?
>>>>>> (lldb) log enable -f /tmp/packates.txt gdb-remote packets
>>>>>> (lldb) process attach --name "<name>" --waitfor
>>>>>> error: attach failed: lost connection
>>>>>> Attached the log output. Maybe it'll make more sense to you than
>>>>>> me.>>>>>> 
>>>>>> That escalated quickly. So I've read through that log. I found
>>>>>> something that says $qVAttachOrWaitSupported#38 with the
>>>>>> following response being $#00. Perhaps I'm reading too much but
>>>>>> is it that it's reporting that it is not supported?>>>>>> 
>>>>>> Does lldb-server need to be compiled in a certain way to add
>>>>>> support for attach wait?>>>>>> 
>>>>>> On Thu, May 31, 2018, at 1:49 PM, Greg Clayton wrote:
>>>>>>> Try enabling logging with:
>>>>>>> (lldb) log enable -f /tmp/packets.txt gdb-remote packets
>>>>>>> And the try the attach. It might be a lldb-server issue?
>>>>>>>> On May 31, 2018, at 9:02 AM, Ryan Lovelett via lldb-dev <lldb-
>>>>>>>> dev at lists.llvm.org> wrote:>>>>>>>> 
>>>>>>>> I am attempting to use: process attach --name "<name>" --
>>>>>>>> waitfor>>>>>>>> 
>>>>>>>> The problem is that it immediately returns error: attach
>>>>>>>> failed: lost connection.>>>>>>>> 
>>>>>>>> Is this something I can troubleshoot further? Or is this not
>>>>>>>> supported on Linux?>>>>>>>> 
>>>>>>>> -- 
>>>>>>>> Ryan Lovelett
>>>>>>>> _______________________________________________
>>>>>>>> lldb-dev mailing list
>>>>>>>> lldb-dev at lists.llvm.org
>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>>>>>> <packates.txt>

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