[pypy-issue] [issue1204] gdb hooks for debugging PyPy

[Dave Malcolm]

New submission from Dave Malcolm <dmalcolm at redhat.com>:

gdb 7 onwards is scriptable using an embedded CPython 2.*, giving the ability to write fragments of Python to add new 
commands, and to tell gdb how to pretty-print data, etc.  (A couple of years ago I wrote such code to make it easier to 
debug CPython; see http://fedoraproject.org/wiki/Features/EasierPythonDebugging )

I'm attaching a script I've written to help debug PyPy.  It's a work in progress so far, but it's able to print RPython 
strings, and some PyPy frame information.

For example, if I run
  $ gdb --eval-command="break pypy_g_PyFrame_run" --eval-command="run" --args pypy
I get this output when the breakpoint is hit:
  Breakpoint 1, pypy_g_PyFrame_run (l_self_11960=Frame for app_main.py:run_toplevel:42) at interpreter_pyframe.c:48

Note how the frame object has been pretty-printed as "Frame for app_main.py:run_toplevel:42"

I'm attaching what a full backtrace looks like with these hooks for a pypy process waiting at the interactive prompt 
(full-backtrace.txt): numerous frames are visible.  Unfortunately, many values are optimized out, though.

Of course this code is specific to the C backend, and it's probably sensitive to translation options - but my feeling is 
that every little helps when debugging the generated C code.

FWIW I've been developing this on a Fedora 17 x86_64 box, using the pypy rpms (which have slightly non-standard 
translation options; see http://pkgs.fedoraproject.org/gitweb/?p=pypy.git;a=blob;f=pypy.spec ).

I copy the file to:
   /usr/lib/debug/usr/lib64/pypy-1.9/pypy.debug-gdb.py
alongside the DWARF data (where I've been editing it in place).

gdb will load this on startup when debugging /usr/lib64/pypy-1.9/pypy (aka /usr/bin/pypy).  My plan is to package this 
file within my rpms so that it's within the debuginfo rpm (I do something similar for CPython on Fedora/RHEL).

Presumably this file should live somewhere in the pypy source tree (where?)  Should I create a branch on bitbucket, and 
hack on it there?

----------
files: pypy.debug-gdb.py
messages: 4543
nosy: dmalcolm, pypy-issue
priority: feature
status: unread
title: gdb hooks for debugging PyPy

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PyPy bug tracker <tracker at bugs.pypy.org>
<https://bugs.pypy.org/issue1204>
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