[PATCH] D42845: Add an option 'allow-all-hosts' to permit lldb debugging inside a Docker container

[Pavel Labath via llvm-commits]

Thanks for checking this. This confirms to me that it should be
possible to make things "just work". Why it does not work is not clear
to me, but I think we should figure that out. I made some experiments

Can you dig a bit deeper into why things are failing _without_ your
patch. The two things I would check is:
- is LLGS being passed the correct address on the command line (172.17.0.2)
- does that address make it all the way to the address-checking code
(TCPSocket::Accept)

In the accept function we have this line
    if (!AddrIn.IsAnyAddr() && AcceptAddr != AddrIn) {
right now that is not triggerring with your patch because of the
IsAnyAddr part, but even without it, the second part should match. If
we figure out why is that not happening, we should be able to fix it.

On 7 February 2018 at 21:46, Alex Blewitt <alblue at apple.com> wrote:
> On 7 Feb 2018, at 07:30, Pavel Labath <labath at google.com> wrote:
>
> On 7 February 2018 at 15:03, Alex Blewitt <alblue at apple.com> wrote:
>
> What I do is set up Docker to forward the connections via the specific ports
> - in effect, the Docker app is listening on localhost:4000, then it routes
> packets through into inside the Docker instance and changes the IP address.
>
> Right, and for the llgs connection, I presume you have a similar
> setup, where docker listens on localhost:4001 and forwards to
> (virtual) 172.17.0.2:4001.
>
>
> So getpeername inside the Docker instance is getting a different IP address
> than the connection that the lldb client thinks it is.
>
>
> Now this is the part I don't get. It's true that the client sends it's
> own hostname as a part of the launch request, but that is currently
> being ignored by the platform:
> GDBRemoteCommunicationServerPlatform.cpp:107
>  // ignore the hostname send from the remote end, just use the ip address
>  // that we're currently communicating with as the hostname
>
> My guess is this is done precisely so that your use case could work.
> And it should work because LLGS will be comparing getpeername() of the
> platform connection with getpeername() of the LLGS one, and these
> should match as both are taken from the inside of the docker image.
> Why it doesn't work is something I'd like to figure out, as I think
> your use case should work out-of-the-box.
>
> Can you repeat your netstat experiment with both of the connections
> (LLGS and platform) active, so we can see how all addresses are
> resolved?
>
>
> Here's what it looks like inside the container - the 4000 is the platform
> server and the 4001 is the child gdbserver process:
>
> # netstat
> Active Internet connections (w/o servers)
> Proto Recv-Q Send-Q Local Address           Foreign Address         State
> tcp        0      0 f6c9d51504e8:4000       172.17.0.1:55212
> ESTABLISHED
> tcp        0      0 f6c9d51504e8:4001       172.17.0.1:58322
> ESTABLISHED
> tcp        0      0 f6c9d51504e8:4000       172.17.0.1:55216
> ESTABLISHED
>
> (in this case, I've restarted the docker image so there's a different name)
>
> # cat /etc/hosts
> 127.0.0.1 localhost
> 172.17.0.2 f6c9d51504e8
>
> This is what the connection looks like from outside the container, looking
> in:
>
> $ netstat -n | grep 400
> tcp4       0      0  127.0.0.1.4001         127.0.0.1.53809
> ESTABLISHED
> tcp4       0      0  127.0.0.1.53809        127.0.0.1.4001
> ESTABLISHED
> tcp4       0      0  127.0.0.1.4000         127.0.0.1.53808
> ESTABLISHED
> tcp4       0      0  127.0.0.1.53808        127.0.0.1.4000
> ESTABLISHED
> tcp4       0      0  127.0.0.1.4000         127.0.0.1.53806
> ESTABLISHED
> tcp4       0      0  127.0.0.1.53806        127.0.0.1.4000
> ESTABLISHED
>
> These are the processes running in the Docker container, with the 0.0.0.0
> signifying the patch working:
>
>    66 pts/0    Sl+    0:00 lldb-server platform --allow-all-hosts --server
> --listen *:4000 --min-gdbserver-port 4001 --max-gdbserver-port
>    70 pts/0    S+     0:00 /usr/bin/lldb-server gdbserver tcp://0.0.0.0:4001
> --native-regs --log-file=/tmp/lldb-gdbserver.log
>
> Alex