gdb使用的python gdb python脚本

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mob6454cc72ae38 2024-01-23 23:59:33

文章标签 gdb使用的python Linux gdb Python xml python 文章分类 Python 后端开发

     调试python脚本一般可通过记录log和使用python自带的pdb模块完成，但凡事总有例外，在以下三种情况时上述方法就无能为力了。
   1 段错误
   2 运行中的daemon程序
   3 core dump
这个时候就需祭出gdb进行调试。python2.6的源码中提供了部分预定义函数以便大家使用gdb调试，我们只需将文件Python-2.6/Misc/gdbinit所包括的内容加入到用户目录下的.gdbinit文件中即可，这样每次启动gdb时会自动完成这些宏的定义。但可惜的是Python2.6.2 gdbini对于pylocals的定义居然有错误，看来是没有随着代码的更新而同步更新。我们只需将 while $_i < f->f_nlocals修改为 while $_i < f->f_code->co_nlocals即可。文章后面所附的几个宏建议也加入的.gdbinit文件中，更多的宏可参考

http://web.archive.org/web/20070915134837/

http://www.mashebali.com/?Python_GDB_macros:The_Macros。

我们首先需要构造一个会造成段错误的python脚本。老实说让python发生段错误并不容易，但通过其外部调用库就很简单了。我们将该文件命名为gdb_test.py

import sys, os, libxml2
 def segv_test():
     s = "<html><body><div><a><a></a></a><a></a></div></body></html>"
     options = libxml2.HTML_PARSE_RECOVER + \
               libxml2.HTML_PARSE_NOERROR + \
               libxml2.HTML_PARSE_NOWARNING
     doc = libxml2.htmlReadDoc(s, None, 'utf-8', options).doc
     ctxt = doc.xpathNewContext()
     nodes = ctxt.xpathEval('//body/node()')
     nodes.reverse()
     for note in nodes:
         nexts = note.xpathEval('node()')
         note.unlinkNode() 
         note.freeNode() //freeNode会将该节点及其子节点释放掉
         nexts[0].unlinkNode() 
         nexts[0].freeNode() //资源已经释放，再次释放会造成段错误 def main():
     segv_test() if __name__ == "__main__":
     main()    使用gdb运行该脚本,我们会得到段错误信息。
 gdb python
 r gdb_test.py *** glibc detected *** double free or corruption (fasttop): 0x08104570 ***
 Program received signal SIGABRT, Aborted.
 [Switching to Thread -1208260928 (LWP 26159)]
 0x00b987a2 in _dl_sysinfo_int80 () from /lib/ld-linux.so.2    键入bt得到如下堆栈信息: 
 (gdb) bt
 #0 0x00b987a2 in _dl_sysinfo_int80 () from /lib/ld-linux.so.2
 #1 0x00c00825 in raise () from /lib/tls/libc.so.6
 #2 0x00c02289 in abort () from /lib/tls/libc.so.6
 #3 0x00c34cda in __libc_message () from /lib/tls/libc.so.6
 #4 0x00c3b56f in _int_free () from /lib/tls/libc.so.6
 #5 0x00c3b94a in free () from /lib/tls/libc.so.6
 #6 0x009812c6 in xmlFreeNode () from /opt/sohumc/lib/libxml2.so.2
 #7 0x0029d7f3 in libxml_xmlFreeNode () from /opt/sohumc/lib/python2.6/site-packages/libxml2mod.so
 #8 0x00780bae in PyCFunction_Call (func=0x8104570, arg=0xd05820, kw=0x6) at Objects/methodobject.c:116
 #9 0x007d8c79 in call_function (pp_stack=0xbff8c48c, oparg=0) at Python/ceval.c:3679
 #10 0x007d6d2b in PyEval_EvalFrameEx (f=0x8124ef4, throwflag=0) at Python/ceval.c:2370
 #11 0x007d8e36 in fast_function (func=0x6, pp_stack=0xbff8c5dc, n=1, na=1, nk=0) at Python/ceval.c:3765
 #12 0x007d89cd in call_function (pp_stack=0xbff8c5dc, oparg=0) at Python/ceval.c:3700
 #13 0x007d6d2b in PyEval_EvalFrameEx (f=0x81242fc, throwflag=0) at Python/ceval.c:2370
 #14 0x007d8e36 in fast_function (func=0x6, pp_stack=0xbff8c72c, n=0, na=0, nk=0) at Python/ceval.c:3765
 #15 0x007d89cd in call_function (pp_stack=0xbff8c72c, oparg=0) at Python/ceval.c:3700
 #16 0x007d6d2b in PyEval_EvalFrameEx (f=0x810a7c4, throwflag=0) at Python/ceval.c:2370
 #17 0x007d8e36 in fast_function (func=0x6, pp_stack=0xbff8c87c, n=0, na=0, nk=0) at Python/ceval.c:3765
 #18 0x007d89cd in call_function (pp_stack=0xbff8c87c, oparg=0) at Python/ceval.c:3700
 #19 0x007d6d2b in PyEval_EvalFrameEx (f=0x8091d0c, throwflag=0) at Python/ceval.c:2370
 #20 0x007d76f9 in PyEval_EvalCodeEx (co=0xb7fa3728, globals=0x6, locals=0xb7f9902c, args=0x0, argcount=0, kws=0x0, kwcount=0, defs=0x0, defcount=0,
     closure=0x0) at Python/ceval.c:2942
 #21 0x007d47cb in PyEval_EvalCode (co=0xb7fa3728, globals=0xb7f9902c, locals=0xb7f9902c) at Python/ceval.c:515
 #22 0x007fbbce in run_mod (mod=0x80ea780, filename=0xbffc6be6 "gdb_test.py", globals=0xb7f9902c, locals=0xb7f9902c, flags=0xbff8ca8c, arena=0x807ef28)
     at Python/pythonrun.c:1330
 #23 0x007fbb58 in PyRun_FileExFlags (fp=0x8091d00, filename=0xbffc6be6 "gdb_test.py", start=257, globals=0xb7f9902c, locals=0xb7f9902c, closeit=1,
     flags=0xbff8ca8c) at Python/pythonrun.c:1316
 #24 0x007fb22d in PyRun_SimpleFileExFlags (fp=0x8091d00, filename=0xbffc6be6 "gdb_test.py", closeit=1, flags=0xbff8ca8c) at Python/pythonrun.c:926
 #25 0x007facc9 in PyRun_AnyFileExFlags (fp=0x8091d00, filename=0xbffc6be6 "gdb_test.py", closeit=1, flags=0xbff8ca8c) at Python/pythonrun.c:731
 #26 0x00808fea in Py_Main (argc=1, argv=0xbff8cbb4) at Modules/main.c:597
 #27 0x080486ae in main (argc=2, argv=0xbff8cbb4) at Modules/python.c:23
    
    pystack和pystackv两个宏可用来查看python内部的栈情况；可以看到程序时执行到freeNode函数时结束， 该函数位于libxml2.py的3141行。
 (gdb) pystack
 /opt/lib/python2.6/site-packages/libxml2.py (3141): freeNode
 gdb_test.py (17): segv_test
 gdb_test.py (21): main
 gdb_test.py (24): <module>

    通过堆栈我们可以看到脚本内部各函数的调用关系， 那么我们如何查看函数内变量情况呢？ 正如大家所， python内部堆栈和函数的调用由PyEval_EvalFrameEx完成的， 一次PyEval_EvalFrameEx意味着一次函数调用，象上面的第19,13,10行分别对应于main, segv_test, freeNode函数， 将gdb定位到对应行后，使用pylocals宏即可查看该函数内部变量的详细情况。
 (gdb) up 13
 #13 0x007d6d2b in PyEval_EvalFrameEx (f=0x81242fc, throwflag=0) at Python/ceval.c:2370
 2370    in Python/ceval.c
 (gdb) pylocals
 s:
 object : '<html><body><div><a><a></a></a><a></a></div></body></html>'
 type    : str
 refcount: 3
 address : 0xb7f64440
 options:
 object : 97
 type    : int
 refcount: 7
 address : 0x8082c20
 doc:
 object : <xmlDoc (None) object at 0xb7cc04ec>
 type    : instance
 refcount: 1
 address : 0xb7cc04ec
 ctxt:
 object : <libxml2.xpathContext instance at 0xb7f70ccc>
 type    : instance
 refcount: 1
 address : 0xb7f70ccc
 nodes:
 object : [<xmlNode ((儓X? object at 0xb7cc0cac>]
 type    : list
 refcount: 2
 address : 0xb7f70a8c
 note:
 object : <xmlNode ((?圶? object at 0xb7cc0cac>
 type    : instance
 refcount: 2
 address : 0xb7cc0cac
 nexts:
 object : [<xmlNode (hhX? object at 0xb7cc750c>, <xmlNode (HXX? object at 0xb7cc76cc>, <xmlNode (@XX? object at 0xb7c9348c>]
 type    : list
 refcount: 1
 address : 0xb7f4ce4c

脚本调试时断点的设置是个很麻烦的东西，我所能想到的有两种方法：1 根据函数的python源码进行断点设置；2 采用sleep函数和ctrl+c来中断程序的运行。无论怎么样使用逐条执行进行调试都是很痛苦的事情，因为这个时候python解释器本身要做很多工作。
由于本身对于python源码不是很熟悉，因此对如何使用gdb对python脚本调试上也只是很粗略的理解，这里权当抛砖引玉，欢迎达人们给出分享的经验。

额外的宏：
 define pbt 
 set $i = 0 
 set $j = 0 
 while $i < 1000 
 select $i 
 if $eip >= &PyEval_EvalFrameEx 
 if $eip < &PyEval_EvalCodeEx 
 echo c frame # 
 p $i 
 echo py frame # 
 p $j 
 set $j = $j+1 
 x/s ((PyStringObject*)f->f_code->co_filename)->ob_sval 
 x/s ((PyStringObject*)f->f_code->co_name)->ob_sval 
 echo line # 
 p f->f_lineno 
 end 
 end 
 set $i = $i+1 
 end 
 end 
 document pbt 
 show python backtrace 
 end define pyattrlist
 set $dict = *(PyDictObject**)(((int)$arg0)+$arg0.ob_type.tp_dictoffset)
 set $i = 0
 set $j = 0
 while $i < $dict.ma_mask
 if 0 != $dict.ma_table[$i].me_value
    echo \nattr#:
    p $j
    x/s ((PyStringObject*)$dict.ma_table[$i].me_key).ob_sval
    pyobjinfo $dict.ma_table[$i].me_value
    set $j = $j+1
 end
 set $i = $i+1
 end
 end
 document pyattrlist
 show pythonic object attributes list
 end define pyattr
 set $dict = *(PyDictObject**)(((int)$arg0)+$arg0.ob_type.tp_dictoffset)
 set $i = 0
 set $j = 0
 while $i < $dict.ma_mask
 if 0 != $dict.ma_table[$i].me_value
    if $j == $arg1
     set $attr = $dict.ma_table[$i].me_value
     echo $attr:
     p $attr
    end
    set $j = $j+1
 end
 set $i = $i+1
 end
 end
 document pyattr
 get pythonic object attribute
 usage: pyattr <pyobj> <attr#>
 atr# correlates to those shown in pyattrlist
 end

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