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"，这个命令可以直接用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()
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~ 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，而且GDB提供了许多API,你想要啥基本都能实现。
注：lldb也支持Python扩展，所以同样的道理可以用于lldb。 References:
- https://undo.io/resources/gdb-watchpoint/python-gdb/
- https://codeyarns.com/2014/07/17/how-to-enable-pretty-printing-for-stl-in-gdb/