python-源码阅读(7)-Cpython调试

python

一. 工作准备

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# locally clone the repo.
git clone https://github.com/python/cpython
# Navigate to the repo directory
cd cpython
# Switch to the version of python you want to work on
git checkout 3.6
# configure a debug build for CPython
./configure --with-pydebug
# build without echoing commands and use 2 cores
make -s -j2

注意：
最好是linux系统

二. 了解python字节码

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>>> import dis
>>> def foo():
...     a = 1
...     a.x
...
>>> dis.dis(foo)
  2           0 LOAD_CONST               1 (1)
              3 STORE_FAST               0 (a)
  3           6 LOAD_FAST                0 (a)
              9 LOAD_ATTR                0 (x)
             12 POP_TOP
             13 LOAD_CONST               0 (None)
             16 RETURN_VALUE

使用dis模块查看python字节码，其中LOAD_CONST指令对于如下

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// Python/ceval.c
   2862 TARGET(LOAD_ATTR) {
   2863     PyObject *name = GETITEM(names, oparg);
   2864     PyObject *owner = TOP();
   2865     PyObject *res = PyObject_GetAttr(owner, name);
   2866     Py_DECREF(owner);
   2867     SET_TOP(res);
   2868     if (res == NULL)
   2869         goto error;
   2870     DISPATCH();
}

gdb 调试

  1. 启动dgb，编写代码例子
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    sabbas@sabbas-VirtualBox:~/Documents/pythondev/cpython
    $ gdb python
    GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
    Copyright (C) 2016 Free Software Foundation, Inc.
    (gdb) run
    Starting program: /home/sabbas/Documents/pythondev/cpython/python 
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
    Python 3.6.2+ (heads/3.6:cb7fdf6, Aug 23 2017, 22:24:16) 
    [GCC 5.4.0 20160609] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>>
    >>> 
    >>> 
    >>> def foo():
    ...     x = 1
    ...     x.a
    ... 
    >>>
  2. 另外启动一个终端 暂停python执行器，提供打入断点机会
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    sabbas@sabbas-VirtualBox:~/Documents/pythondev/cpython
    $ pkill python -SIGTRAP
  3. 回到dgb调试打断点
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    sabbas@sabbas-VirtualBox:~/Documents/pythondev/cpython
    $ gdb python
    GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
    Copyright (C) 2016 Free Software Foundation, Inc.
    (gdb) run
    Starting program: /home/sabbas/Documents/pythondev/cpython/python 
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
    Python 3.6.2+ (heads/3.6:cb7fdf6, Aug 23 2017, 22:24:16) 
    [GCC 5.4.0 20160609] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>>
    >>> 
    >>> 
    >>> def foo():
    ...     x = 1
    ...     x.a
    ... 
    >>>
    Program received signal SIGTRAP, Trace/breakpoint trap.
    0x00007ffff71dd573 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:84
    84 ../sysdeps/unix/syscall-template.S: No such file or directory.
    (gdb) b Python/ceval.c:2855
    Breakpoint 1 at 0x5418d7: file Python/ceval.c, line 2855.
    (gdb)c
    Continuing.
    >>>
  4. 函数调用,断在cpython中了
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    >>> foo()
    Breakpoint 1, _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:2855
    2855             PyObject *name = GETITEM(names, oparg);
    (gdb)
  5. 使用dbg相关命令查看cpython中变量，等等等