[lldb-dev] LLDB Process Attach Failed When Waiting

Mon Jun 4 16:04:22 PDT 2018

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 <mailto: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/ <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 <mailto: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 <mailto: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 <mailto:lldb-dev at lists.llvm.org>
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev>
>>>>> <packates.txt>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/lldb-dev/attachments/20180604/e14dacf3/attachment-0001.html>