[Lldb-commits] [lldb] [lldb][Docs] Add page about debugging lldb itself (PR #65332)

[David Spickett via lldb-commits]

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+Debugging LLDB
+==============
+
+This page details various ways to debug LLDB itself and other LLDB tools. If
+you want to know how to use LLDB in general, please refer to
+:doc:`/use/tutorial`.
+
+As LLDB is generally split into 2 tools, ``lldb`` and ``lldb-server``
+(``debugserver`` on Mac OS), the techniques shown here will not always apply to
+both. With some knowledge of them all, you can mix and match as needed.
+
+In this document we refer to the initial ``lldb`` as the debugger and the
+program being debugged as the debugee.
+
+Building For Debugging
+----------------------
+
+To build LLDB with debugging information add the following to your CMake
+configuration:
+
+::
+
+  -DCMAKE_BUILD_TYPE=Debug \
+  -DLLDB_EXPORT_ALL_SYMBOLS=1
+
+Note that the ``lldb`` you will use to do the debugging does not itself need to
+have debug information.
+
+Then build as you normally would.
+
+Debugging ``lldb``
+------------------
+
+The simplest scenario is where we want to debug a local execution of ``lldb``
+like this one:
+
+::
+
+  ./bin/lldb test_program
+
+LLDB is like any other program, so you can use the same approach.
+
+::
+
+  ./bin/lldb -- ./bin/lldb /tmp/test.o
+
+That's it. At least, that's the minimum. There's nothing special about LLDB
+being a debugger that means you can't attach another debugger to it like any
+other program.
+
+What can be an issue is that both debuggers have command line interfaces which
+makes it very confusing which one is which:
+
+::
+
+  (the debugger)
+  (lldb) run
+  Process 1741640 launched: '<...>/bin/lldb' (aarch64)
+  Process 1741640 stopped and restarted: thread 1 received signal: SIGCHLD
+
+  (the debugee)
+  (lldb) target create "/tmp/test.o"
+  Current executable set to '/tmp/test.o' (aarch64).
+
+Another issue is that when you resume the debugee, it will not print the
+``(lldb)`` prompt because as far as it knows it hasn't changed state. A quick
+way around that is to type something that is clearly not a command and hit
+enter.
+
+::
+
+  (lldb) Process 1742266 stopped and restarted: thread 1 received signal: SIGCHLD
+  Process 1742266 stopped
+  * thread #1, name = 'lldb', stop reason = signal SIGSTOP
+      frame #0: 0x0000ffffed5bfbf0 libc.so.6`__GI___libc_read at read.c:26:10
+  (lldb) c
+  Process 1742266 resuming
+  notacommand
+  error: 'notacommand' is not a valid command.
+  (lldb)
+
+You could just remember whether you are in the debugger or the debugee but
+it's thinking overhead, and for interrupt based events you simply may not be
+able to know.
+
+Here are some better approaches. First, you could use another debugger like GDB
+to debug LLDB. Perhaps an IDE like XCode or Visual Studio Code. Something which
----------------
DavidSpickett wrote:

Done.

https://github.com/llvm/llvm-project/pull/65332