Updating remote process capture FAQ

README.md

@@ -101,17 +101,50 @@ Try clang instead of gcc (fingers crossed). See [clang comparison](http://clang.
 
 #### How do I attach to a running process?
 
-To be able to attach, the "attacher" needs to have special permissions. The
-easiest method is to run a debug server as 'sudo' and connect to it.
-See the question below.
+To be able to attach a running process, the lldb process needs to have a
+special capability to enable usage of the [*ptrace*] system call. [For security
+reasons], this system call is restricted to the children processes of the
+process doing the capture, which is the default way that `lldb` (or any debugger) works.
+
+But you can enable capturing of a running process by globally disabling scoping of
+the ptrace system call:
+
+```
+sysctl -w kernel.yama.ptrace_scope=0
+```
+
+But don't forget to set it back to `1` when you're done to keep your system safe.
+
+You'd have two other ways to attach to a running process, but because *lldb.vim*
+uses python bindings and not the `lldb` executable, those can only work with `lldb-server`.
+So please read [the following FAQ entry on how to run a remote server][remote-debug].
+
+Instead of disabling `ptrace` scoping globally, you can as well disable it just for
+the `lldb-server` executable:
+
+```
+sudo setcap cap_sys_ptrace=eip /usr/bin/lldb-server
+```
+
+To revert the setting:
+
+```
+sudo setcap -r /usr/bin/lldb-server
+```
+
+Another way would be to run `lldb-server` as root, as bypassing `ptrace` scoping is
+amongst the root privileges.
+
+[*ptrace*]:https://en.wikipedia.org/wiki/Ptrace
+[For security reasons]:http://askubuntu.com/a/153970/583565
 
 #### Remote debugging does not work!!
 
 I haven't been able to get `gdbserver`, `lldb-gdbserver` or `lldb-server gdbserver`
 to work properly with the python API. But the following works; run:
 
 ```
-# use sudo if you want to attach to a running process
+# use sudo if you want to attach to a running process or setcap
 $ lldb-server platform --listen localhost:2345
 
 # in older versions of lldb, use this instead
@@ -128,3 +161,64 @@ on port 2345. Now, from the client (the plugin), run:
 ```
 
 For more info on this, see [Remote Debugging](http://lldb.llvm.org/remote.html).
+
+#### How to debug an interactive commandline process?
+
+You'll need to make it possible to capture a remote process with `lldb`, see the above
+two answers for more details.
+
+If you choose to disable globally `ptrace` scoping, you can run the following command
+to open a new terminal buffer with your interactive command line program (once your
+debugging session is started):
+
+``` viml
+:1wincmd w | vsplit | term ./debugee -args | exec(":LL process attach -p " . b:terminal_job_pid)
+```
+
+Then you can setup breakpoints, watchpoints… and start the execution with `:LL continue`.
+(don't forget to change `debugee` with your program name).
+
+If you prefer to use a debugging server instead, you can add the following viml function
+in your `vimrc`:
+
+``` viml
+function! LLSpawn(target, ...)
+  let port = a:0 >= 2 ? a:1 : 2345
+  if !exists('g:lldb#remote_server')
+    if !system('pgrep "lldb-server"')
+        exe ":!lldb-server --listen " . host . ":" . port&
+        # or
+        # exe ":!sudo lldb-server --listen " . host . ":" . port&
+        sleep 1
+        echomsg 'lldb-server started...'
+    else
+        echomsg 'lldb-server already running...'
+    endif
+    LL platform select remote-linux
+    exe "LL platform connect connect://" . host . ":" . port
+    let g:lldb#remote_server = 1
+  endif
+  1wincmd w
+  vsplit
+  exe ":term ". a:target
+  exe ":LL process attach -p " . b:terminal_job_pid
+  2wincmd w
+endfunction
+```
+
+then once your debugging session has been started, you can run:
+
+``` viml
+call LLSpawn('./debuggee --args') " or
+call LLSpawn('./debuggee --args', '4242')
+```
+
+which will start an `lldb-server` as suggested in the [former FAQ entry][remote-debug],
+start the *debuggee* process and attach it, if no server is already runnning. If you choose to start the process as root, just
+prefix the `lldb-server` call with `sudo`, otherwise you need to disable `ptrace` 
+scoping in any way suggested [above][attach-process].
+
+[attach-process]:#how-do-I-attach-to-a-running-process
+[remote-debug]:#remote-debugging-does-not-work
+
+