【转载】【GDB】GDB with Python
作者：薛定谔的喵
链接：https://zhuanlan.zhihu.com/p/152274203
来源：知乎
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你还在用GDB调试程序吗？
如果是，那么我们是同道中人。但是你知道GDB有一个很强大的功能，Python scripting嘛？
如果是的，那么恭喜你，你是一个大牛。
本文主要讲述如何使用Python来提高你的gdb调试技能， 让你从繁重的重复的工作里面挣脱出来呼吸新鲜空气。
首先，第一件事，使用gdb7.x以上的版本，最好9.x的。因为Python的支持是从gdb7.0（2009年？）开始的。
进入正题
gdb本来就支持自定义脚本辅助调试，为什么还要用Python脚本呢？因为自定义脚本的语法比较老，不如写Python欢快。如果你喜欢用原来的自定义脚本方法，那也是可以的。
借助Python，你可以将难看的数据变得好看，
借助Python，你可以将重复的工作变成一个命令，
借助Python，你可以更快的调试bug，
借助Python，你可以装逼，哈哈哈
……
将难看的数据变得好看
以下面的代码为例
#include <map> #include <iostream> #include <string> using namespace std; int main() { std::map<string, string> lm; lm["good"] = "heart"; // 查看map 里面内容 std::cout<<lm["good"]; }
当代码运行到std<<cout时, 你想查看map里面的内容，如果没有python和自定义的脚本，print lm看到的是
$2 = {_M_t = {
_M_impl = {<std::allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >> = {<__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >> = {<No data fields>}, <No data fields>}, <std::_Rb_tree_key_compare<std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >> = {
_M_key_compare = {<std::binary_function<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool>> = {<No data fields>}, <No data fields>}}, <std::_Rb_tree_header> = {_M_header = {
_M_color = std::_S_red, _M_parent = 0x55555556eeb0,
_M_left = 0x55555556eeb0, _M_right = 0x55555556eeb0},
_M_node_count = 1}, <No data fields>}}}
但是当你在gdb9.2里面输入print lm的时候，你看到的将是
(gdb) p lm $3 = std::map with 1 element = {["good"] = "heart"}
map里面有什么一清二楚。这是因为gdb9.x自带了一系列标准库的Python pretty priniter。 如果你使用的是gdb7.x，那么你可以手动的导入这些pretty printer实现同样的效果。具体步骤如下：
- 下载pretty printer: svn co svn://http://gcc.gnu.org/svn/gcc/trunk/libstdc++-v3/python
- 在gdb里面输入(将路径改成你下载的路径)：
python import sys sys.path.insert(0, '/home/maude/gdb_printers/python') from libstdcxx.v6.printers import register_libstdcxx_printers register_libstdcxx_printers (None) end
这样你就可以放心使用了~
详细请看：
https://sourceware.org/gdb/wiki/STLSupport
https://codeyarns.com/2014/07/17/how-to-enable-pretty-printing-for-stl-in-gdb/
将重复的工作变成一个命令
比如在调试的时候，你知道当前栈指向一个字符串，但是你不知道具体在哪里，你想遍历这个栈将它找出来，那么你可以借助Python自定义一个命令"stackwalk"，这个命令可以直接Python代码遍历栈，将字符串找出来。
##################################################### # Usage: to load this to gdb run: # (gdb) source ..../path/to/<script_file>.py import gdb class StackWalk(gdb.Command): def __init__(self): # This registers our class as "StackWalk" super(StackWalk, self).__init__("stackwalk", gdb.COMMAND_DATA) def invoke(self, arg, from_tty): # When we call "StackWalk" from gdb, this is the method # that will be called. print("Hello from StackWalk!") # get the register rbp = gdb.parse_and_eval('$rbp') rsp = gdb.parse_and_eval('$rsp') ptr = rsp ppwc = gdb.lookup_type('wchar_t').pointer().pointer() while ptr < rbp: try: print('pointer is {}'.format(ptr)) print(gdb.execute('wc_print {}'.format(ptr.cast(ppwc).dereference()))) print('===') except: pass ptr += 8 # This registers our class to the gdb runtime at "source" time. StackWalk() 更快的调试bug 当你调试多线程的时候，你发现callstack 一堆，而且好多都是重复的，如果它们可以自动去重或者折叠多好，这样你只需要关注一小部分。好消息！Python可以让你用一个命令就可以轻松搞定。而且已经有人写好了相应的代码，你只需要导入即可。详细介绍请看https://fy.blackhats.net.au/blog/html/2017/08/04/so_you_want_to_script_gdb_with_python.html # From https://fy.blackhats.net.au/blog/html/2017/08/04/so_you_want_to_script_gdb_with_python.html ##################################################### # # Usage: to load this to gdb run: # (gdb) source ..../path/to/debug_naughty.py # # To have this automatically load, you need to put the script # in a path related to your binary. If you make /usr/sbin/foo, # You can ship this script as: # /usr/share/gdb/auto-load/ <PATH TO BINARY> # /usr/share/gdb/auto-load/usr/sbin/foo # # This will trigger gdb to autoload the script when you start # to acces a core or the live binary from this location. # import gdb class StackFold(gdb.Command): def __init__(self): super(StackFold, self).__init__("stackfold", gdb.COMMAND_DATA) def invoke(self, arg, from_tty): # An inferior is the 'currently running applications'. In this case we only # have one. stack_maps = {} # This creates a dict where each element is keyed by backtrace. # Then each backtrace contains an array of "frames" # inferiors = gdb.inferiors() for inferior in inferiors: for thread in inferior.threads(): try: # Change to our threads context thread.switch() # Get the thread IDS (tpid, lwpid, tid) = thread.ptid gtid = thread.num # Take a human readable copy of the backtrace, we'll need this for display later. o = gdb.execute('bt', to_string=True) # Build the backtrace for comparison backtrace = [] gdb.newest_frame() cur_frame = gdb.selected_frame() while cur_frame is not None: if cur_frame.name() is not None: backtrace.append(cur_frame.name()) cur_frame = cur_frame.older() # Now we have a backtrace like ['pthread_cond_wait@@GLIBC_2.3.2', 'lazy_thread', 'start_thread', 'clone'] # dicts can't use lists as keys because they are non-hashable, so we turn this into a string. # Remember, C functions can't have spaces in them ... s_backtrace = ' '.join(backtrace) # Let's see if it exists in the stack_maps if s_backtrace not in stack_maps: stack_maps[s_backtrace] = [] # Now lets add this thread to the map. stack_maps[s_backtrace].append({'gtid': gtid, 'tpid' : tpid, 'bt': o} ) except Exception as e: print(e) # Now at this point we have a dict of traces, and each trace has a "list" of pids that match. Let's display them for smap in stack_maps: # Get our human readable form out. o = stack_maps[smap][0]['bt'] for t in stack_maps[smap]: # For each thread we recorded print("Thread %s (LWP %s))" % (t['gtid'], t['tpid'])) print(o) # This registers our class to the gdb runtime at "source" time. StackFold()
等等！还有好多，毕竟Python图灵完备，只要GDB提供相应的API,你想要啥都能实现。
会了这些，你就可以向新手装逼去了
References:
1 https://undo.io/resources/gdb-watchpoint/python-gdb/
2 https://codeyarns.com/2014/07/17/how-to-enable-pretty-printing-for-stl-in-gdb/
