Add a (small) GDB tips section

advanced-tools/gdb.rst

@@ -324,3 +324,54 @@ auto-load safe. One way to achieve this is to add a line like the following
 to ``~/.gdbinit`` (edit the specific list of paths as appropriate)::
 
     add-auto-load-safe-path ~/devel/py3k:~/devel/py32:~/devel/py27
+
+
+GDB Tips
+========
+
+Learning to use GDB effectively improves your chances of successfully
+debugging problems with Python's internals.  The tips here aren't yet
+organized in any particular way.  Over time, as the section grows,
+hopefully useful organization will become apparent.
+
+Saving and Loading Breakpoints
+------------------------------
+
+With extended exposure to particular parts of the Python runtime, you
+might find it helpful to define a routine set of breakpoints and
+commands to execute when they are hit.  (These might be appropriate to
+a specific debugging/development task, or more generally useful.)  To
+make using multiple semi-static breakpoints easier to use, you can
+save breakpoints to a file and load them in future sessions.  For
+example, you can save your current breakpoints to the file
+``python.brk`` with this command::
+
+  save breakpoints python.brk
+
+You can edit the file to your heart's content, then load it in a later
+session::
+
+  source python.brk
+
+
+Breaking at Labels
+------------------
+
+You will most often set breakpoints at the start of functions, but
+this approach is less helpful when debugging the runtime virtual
+machine, since the main interpreter loop function,
+``_PyEval_EvalFrameDefault``, is well over 4,000 lines long as of Python 3.12.
+Fortunately, among the `many ways to set breakpoints
+<https://sourceware.org/gdb/onlinedocs/gdb/Specify-Location.html>`_,
+you can break at C labels, such as those generated for computed gotos.  If you are
+debugging an interpreter compiled with computed goto support
+(generally true, certainly when using GCC), each instruction will be
+prefaced with a label named ``TARGET_<instruction>``, e.g.,
+``TARGET_LOAD_CONST``.  You can then set a breakpoint with a command
+like::
+
+  break ceval.c:_PyEval_EvalFrameDefault:TARGET_LOAD_CONST
+
+Add commands, save to a file, then reload in future sessions without
+worrying that the starting line number of individual instructions
+change over time.