你还在用GDB调试程序吗?
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2020-09-22 20:57
极市导读
借助Python scripting功能,使用者能够提高自己的GDB调试技能,轻松解决繁复的工作。>>加入极市CV技术交流群,走在计算机视觉的最前沿
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
#include
#include
using namespace std;
int main() {
std::map
lm; lm["good"] = "heart";
// 查看map 里面内容
std::cout<
}
当代码运行到std< 但是当你在gdb9.2里面输入print lm的时候,你看到的将是 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): 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/ 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。 Note: wc_print是我写的另外一个简单Python命令,用于打印给定地址的宽字符串,具体实现留作习题~ 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 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~$2 = {_M_t = {
_M_impl = {
_M_key_compare = {
_M_color = std::_S_red, _M_parent = 0x55555556eeb0,
_M_left = 0x55555556eeb0, _M_right = 0x55555556eeb0},
_M_node_count = 1},
(gdb) p lm
$3 = std::map with 1 element = {["good"] = "heart"}
python
import sys
sys.path.insert(0, '/home/maude/gdb_printers/python')
from libstdcxx.v6.printers import register_libstdcxx_printers
register_libstdcxx_printers (None)
end
将重复的工作变成一个命令
#####################################################
# Usage: to load this to gdb run:
# (gdb) source ..../path/to/
import gdb
class StackWalk(gdb.Command):
def __init__(self):
# This registers our class as "StackWalk"
super(StackWalk, self).__init__("stackwalk", gdb.COMMAND_DATA)
def invoke(self, arg, from_tty):
# When we call "StackWalk" from gdb, this is the method
# that will be called.
print("Hello from StackWalk!")
# get the register
rbp = gdb.parse_and_eval('$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()
更快地调试bug
# 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/
# /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()
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