如何使用gdb捕获函数返回false的时刻? [英] How can I use gdb to catch the moment when a function returns false?

问题描述

如何检测函数bool f()返回false的时刻?

How can I detect the moment when my function bool f() returns false?

f具有复杂的if语句，该语句返回true或false，并且为所有部分设置断点会很昂贵.

f has complex if statements that returns true or false, and it is costly to make breakpoints for all parts.

推荐答案

您可以尝试使用一些Python代码:

you can try with a bit of Python code:

import gdb
class FunctionFinishBreakpoint (gdb.FinishBreakpoint):
    def __init__ (self):
        gdb.FinishBreakpoint.__init__(self, gdb.newest_frame(), 
                                      internal=True)
        self.silent = True 

    def stop(self):
        #print("after: {}".format(int(self.return_value)))
        return not int(self.return_value)

class FunctionBreakpoint(gdb.Breakpoint):
    def __init__ (self, spec):
        gdb.Breakpoint.__init__(self, spec)
        self.silent = True

    def stop (self):
        #print("before")
        FunctionFinishBreakpoint() # set breakpoint on function return

        return False # do not stop at function entry

FunctionBreakpoint("test")

将其保存在finish.py文件中，根据需要对其进行编辑，然后从GDB中获取它，或者在python ... end或python-interactive(pi)中运行它.

Save that in a finish.py file, edit it to your needs and source it from GDB, or run it between python ... end or in python-interactive (pi).

此代码创建一个FunctionBreakpoint，每次按下函数test时都会触发FunctionBreakpoint.stop.回调是静默的，仅创建FunctionFinishBreakpoint，该回调在当前帧的末尾(即，函数的末尾)停止.第二个停靠点调用FunctionFinishBreakpoint.stop，它测试返回值的计算结果为true还是false.如果它不是"true"，它将告诉GDB停止执行.

This code creates a FunctionBreakpoint, that triggers FunctionBreakpoint.stop eachtime function test is hit. The callback is silent, and only creates a FunctionFinishBreakpoint, that stops at the end of the current frame (ie, at the end of your function). That second stop calls FunctionFinishBreakpoint.stop, which tests if the return value evaluates to true or false. If it is "not true", it tells GDB to stop the execution.

文档参考:

• 使用Python操作断点
• 完成断点

• Manipulating breakpoints using Python
• Finish Breakpoints

(gdb.FinishBreakpoint为此被添加到GDB Python接口中，我自己是:-)

(gdb.FinishBreakpoint was added to GDB Python interface for that very purpose, by myself :-)

(我上次检查时，这些FinishBreakpoint存在效率问题，如果经常调用函数，您可能会注意到它)

(last time I checked, there was an efficiency problem with these FinishBreakpoint, you may notice it if your function is called very often)

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