在 Ubuntu 下用 gdb debug CPython

用法和其它 library 稍微不同, 安裝 python-dbg 後, 是提供另一個含有 debug symbol 的 python 執行檔 python2.7-dbg, 而不是 gdb 自己另外載入 python 的 debug symbol。

可從 dpkg -L python-dbg 的結果得知這事:

$ dpkg -L python2.7-dbg | grep bin/python
/usr/lib/debug/usr/bin/python2.7-gdb.py
/usr/lib/debug/usr/bin/python2.7
/usr/bin/python2.7-dbg
/usr/bin/python2.7-dbg-config
/usr/lib/debug/usr/bin/python2.7-dbg-gdb.py
$ nm /usr/bin/python2.7
nm: /usr/bin/python2.7: no symbols
$ nm /usr/bin/python2.7-dbg | head
                 U ASN1_INTEGER_get@@OPENSSL_1.0.0
                 U ASN1_STRING_data@@OPENSSL_1.0.0
                 U ASN1_STRING_length@@OPENSSL_1.0.0
                 U ASN1_STRING_to_UTF8@@OPENSSL_1.0.0
                 U ASN1_TIME_print@@OPENSSL_1.0.0
                 U ASN1_item_d2i@@OPENSSL_1.0.0
00000000008857e0 d AST_type
0000000000967588 b Add_singleton
00000000009675e8 b Add_type
0000000000967560 b And_singleton

實際執行的結果:

$ gdb --args python2.7-dbg -c 'import time; time.sleep(10)'
GNU gdb (Ubuntu/Linaro 7.4-2012.02-0ubuntu2) 7.4-2012.02
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
...
Reading symbols from /usr/bin/python2.7-dbg...done.
(gdb) r
Starting program: /usr/bin/python2.7-dbg -c import\ time\;\ time.sleep\(10\)
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
^C
Program received signal SIGINT, Interrupt.
0x00007ffff69ad003 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:82
82      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) bt
#0   __select_nocancel at ../sysdeps/unix/syscall-template.S:82
#1   floatsleep at ../Modules/timemodule.c:943
#2   time_sleep at ../Modules/timemodule.c:206
#3   PyCFunction_Call at ../Objects/methodobject.c:81
#4   call_function at ../Python/ceval.c:4021
#5   PyEval_EvalFrameEx at ../Python/ceval.c:2666
#6   PyEval_EvalCodeEx at ../Python/ceval.c:3253
#7   PyEval_EvalCode at ../Python/ceval.c:667
#8   run_mod at ../Python/pythonrun.c:1353
#9   PyRun_StringFlags at ../Python/pythonrun.c:1316
#10  PyRun_SimpleStringFlags at ../Python/pythonrun.c:969
#11  Py_Main at ../Modules/main.c:583
#12  main at ../Modules/python.c:23

順便備忘一下相關的文章: Debugging C/C++ and CPython using GDB 7′s new Python extension support 提到如何在 gdb 內使用 python extension 來 debug python code, 可以從 gdb 內看到 C 函式對回去 python script 的檔名和行數。