识别导致内存错误的变量 [英] Identify variable causing memory error

问题描述

所以我现在遇到了一个奇怪的错误，并找到一些很好的方向，以确定问题。

基本上我看到的是一个段故障。症状如下：

1. 只有在程序处于释放模式而不是调试模式时才会发生。



2. 它显示为一个segfault，GDB告诉我它在 _list_release / _free（）
   
   

   程序接收信号SIGSEGV ，分段错误。

   
   
   

   0xb0328af8在/ usr / qnx650 / target / qnx6 / x86 / lib的_list_release /libc.so.3

   
   
   

   （gdb）bt

   
   
   

   0 0xb0328af8在_list_release（）从/usr/qnx650/target/qnx6/x86/lib/libc.so.3

   
   
   

   1 0xb032a464在__free（）从/usr/qnx650/target/qnx6/x86/lib/libc.so.3,/code >

   
   
   

   2 0xb0329f7d in free（）from /usr/qnx650/target/qnx6/x86/lib/libc.so.3



3. 我可以在函数结束之前打印所有局部变量，因此它不是双重自由。

上次发生这种情况是一个内存错误，适合所有这些问题。恼火这个时候我找不到问题。

我想要做的是：

1. 额外有用：如何在调试模式下强制此错误，那么GDB将更有帮助。


2. 什么是跟踪什么小bug是导致问题的最好方法。 注意：我无法使用valgrind，它不能在我正在使用的操作系统（QNX）上工作

任何帮助将是伟大的。

解决方案

它显示为一个segfault，GDB告诉我它在_list_release / _free / free（）

一般来说， code>是堆损坏的迹象（双重释放，写空闲内存，释放未分配（例如堆栈或全局）内存或堆缓冲区溢出）。

我没有使用任何动态记忆

>是。事实上，你通过其他库间接地这样做是无关紧要的。

我可以在函数结束之前打印所有局部变量，

很多评论者已经说过，你的结论并不是这样：你可以访问免费的内存

如何在Debug模式下强制这个错误，那么GDB会更有帮助





• 您可以使用'-O2 -g'信息已启用）。


• GDB可能不会更有帮助--GDB在调试堆损坏方面没有用。









什么是跟踪什么小bug的最好方法




您有以下选择：






• 将您的代码移植到一个平台，您可以使用 Valgrind 或 AddressSanitizer


• 使用许多调试malloc实现（dmalloc，mpatrol等）之一。 QNX有一个。


• 仔细阅读代码，确保不要向可能的malloc缓冲区写入更多的数据。





So I have run into a weird error a few times now and im looking for some good directions as to identify the problem.

Basically what I am seeing is a seg-fault. The symptoms are as follows:

1. It occurs only when the program is in release mode, not in debug.

2. It appears as a segfault and GDB tells me that it is in _list_release/_free()/free() at the end of a function.

   Program received signal SIGSEGV, Segmentation fault.

   0xb0328af8 in _list_release () from /usr/qnx650/target/qnx6/x86/lib/libc.so.3

   (gdb) bt

   0 0xb0328af8 in _list_release () from /usr/qnx650/target/qnx6/x86/lib/libc.so.3

   1 0xb032a464 in __free () from /usr/qnx650/target/qnx6/x86/lib/libc.so.3

   2 0xb0329f7d in free () from /usr/qnx650/target/qnx6/x86/lib/libc.so.3

3. I am not using any dynamic memory (except for what might appear in Eigen (or other libraries)

4. I can print all local variables just before the end of the function, so its not a double free.

Last time this happened it was a memory fault which fits all of these problems. Annoyingly this time i cannot find the problem.

What i would like to do is the following:

1. This would be extra useful: How can I force this error in Debug mode, then GDB would be way more helpful.
2. What is the best way to track down what little bugger is causing the problem. NOTE: I cannot use valgrind, it does not work on the operating system i am using (QNX)

Any help would be great.

解决方案

It appears as a segfault and GDB tells me that it is in _list_release/_free()/free()

Generally, any crash in free() is a sign of heap corruption (a double free, a write to free'd memory, freeing unallocated (e.g. stack or global) memory, or an overflow of a heap buffer).

I am not using any dynamic memory

Yes, you are. The fact that you do so indirectly via other libraries is irrelevant.

I can print all local variables just before the end of the function, so its not a double free.

As many commenters already said, your conclusion doesn't follow: you can access free'd memory just fine, and it may even still contain sensible values.

How can I force this error in Debug mode, then GDB would be way more helpful.

• You can build with '-O2 -g' (a "release" mode but with debug info enabled).
• GDB will likely not be more helpful -- GDB is somewhat useless in debugging heap corruption.

What is the best way to track down what little bugger

You have a few choices:

• Port your code to a platform where you can use Valgrind or AddressSanitizer
• Use one of many debugging malloc implementations (dmalloc, mpatrol, etc.). QNX has one.
• Read the code very carefully, making sure that you don't write more data to possibly-malloc'd buffers than you are supposed to.

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