[lldb-dev] [llvm-dev] Remotely launching a new process with LLDB

Tue Nov 28 11:02:24 PST 2017

lldb-server can be launched in two ways:
1 - platform connection mode
2 - debug a single process mode

LLDB has two ways to connect to a remote process:
1 - you launch the GDB server yourself and attach to it
2 - you launch lldb-server in platform mode, connect to the platform, and then just debug like you normally would on a local machine.

When you launch the GDB server yourself as mentioned in step 1 above, you can do:

remote.foo.com% lldb-server gdbserver 1234 -- /bin/ls -lAF

Then attach to it yourself:

local.foo.com% lldb
(lldb) process connect connect://remote.foo.com:1234 <connect://remote.foo.com:1234>

When you want an lldb-server to do the work of startup on the GDB server for you:

remote.foo.com% lldb-server platform --server --listen 1234

Then you select the remote platform and connect to it with LLDB:

local.foo.com <http://local.foo.com/>% lldb
(lldb) platform select remote-macosx 
  Platform: remote-macosx
 Connected: no
(lldb) platform connect connect://localhost:1234
  Platform: remote-macosx
    Triple: x86_64-apple-macosx
OS Version: 10.12.6 (16G1036)
    Kernel: Darwin Kernel Version 16.7.0: Wed Oct  4 00:17:00 PDT 2017; root:xnu-3789.71.6~1/RELEASE_X86_64
  Hostname: gclayton-pro
 Connected: yes
WorkingDir: /Users/gclayton

Now LLDB has a "platform" connection to the remote machine that can start up the GDB server for you. Also note that the platform states what its working directory is (which defaults to the directory it was launched in).

If you want to launch a locally built executable on the remote side, now you can do:

(lldb) file a.out
(lldb) run

This will cause LLDB to create a target with the "a.out" executable that you cross built. Then you "run" and this will cause LLDB to upload "a.out" to the platform's current working directory only if the file has changed. The platform connection allows us to transfer files, but also allows us to get the MD5 checksum of the file on the other end in the current working directory and only upload the file if it has changed. If you don't want the "a.out" executable to be uploaded to the current platform working directory you can do to specify where the executable will be uploaded to:

(lldb) file /local/path/to/a.out
# Get the lldb.SBModule for "/local/path/to/a.out" in the local variable named "m":
(lldb) script m = lldb.target.module['a.out']
# Set the platform path for the executable to "/bin/a.out":
(lldb) script m.SetPlatformFileSpec("/bin/a.out")
(lldb) run

Now when you run your program, the program will be uploaded to "/bin/a.out" instead of the the current working directory of the platform.

You can also change the platform working directory if you are connected to the platform

(lldb) platform settings -w /tmp

And you can verify it worked using "platform status":

(lldb) platform status
  Platform: remote-macosx
    Triple: x86_64-apple-macosx
OS Version: 10.12.6 (16G1036)
    Kernel: Darwin Kernel Version 16.7.0: Wed Oct  4 00:17:00 PDT 2017; root:xnu-3789.71.6~1/RELEASE_X86_64
  Hostname: gclayton-pro
 Connected: yes
WorkingDir: /private/tmp

If you want to attach to a remote process, you can list the processes if you are connected:

(lldb) platform process list
223 matching processes were found on "remote-macosx"
PID    PARENT USER       TRIPLE                   NAME
====== ====== ========== ======================== ============================
68881  96266  (null)     x86_64-apple-macosx      lldb-server
68639  90652             x86_64-apple-macosx      lldb
67830  1                 x86_64-apple-macosx      helpd
67737  1                 x86_64-apple-macosx      com.apple.iCloudHelper

...

Then attach:

(lldb) attach 68639

Let me know if you have any questions.

Greg Clayton

> On Nov 28, 2017, at 9:29 AM, Adrian Prantl via lldb-dev <lldb-dev at lists.llvm.org> wrote:
> 
> I would recommend asking this on the lldb mailing list instead.
> 
> -- adrian
> 
>> On Nov 26, 2017, at 8:30 AM, Lior Halphon via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
>> I'm trying to remotely launch and debug a new process with lldb without much success.
>> 
>> Attaching to an already launched process works well by running these commands:
>> 
>> process connect <url>
>> process attach -P gdb-remote --pid <pid>
>> But if I want debugserver to launch the executable by itself I'm running into troubles. Especially, I have no clue what arguments should I pass to target
>>  create.
>> 
>> According to this page <https://lldb.llvm.org/remote.html> LLDB "will transparently take care of [..] downloading the executable in order to be able to debug", yet target
>>  create seem to always require a local file. If I specify the remote file via -r I get either unable
>>  to open target file or remote
>>  --> local transfer without local path is not implemented yet errors. If I set the target to a local file (such as a local copy of the remote's loader executable) without using -r, then attempt to run process
>>  launch -p gdb-remote -s <remote path> LLDB will attempt running the local path on the remote machine and fail.
>> 
>> What are the correct commands I need to use in order to launch a remote process?
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
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