矮人错误:找不到DIE [英] Dwarf Error: Cannot find DIE

问题描述

在XCode 4的C ++项目中调试分段错误时，我遇到很多麻烦.

I am having a lot of trouble debugging a segmentation fault in a C++ project in XCode 4.

仅当我使用"LLVM 2.0"编译器选项进行构建并使用-O3优化时，才会出现段错误.据我了解，当使用优化时，调试选项有限，但这是在gdb打开的情况下在Xcode中运行后得到的调试输出:

I only get a segfault when I built with the "LLVM 2.0" compiler option and use -O3 optimization. From what I understand, there are limited debugging options when one is using optimization, but here is the debug output I get after I run in Xcode with gdb turned on:

warning: Got an error handling event: "Dwarf Error: Cannot find DIE at 0x3be2 referenced from DIE at 0x11d [in module /Users/imran/Library/Developer/Xcode/DerivedData/cgo-hczcifktgscxjigfphieegbpxxsq/Build/Products/Debug/cgo]".
No memory available to program now: unsafe to call malloc

此后，我无法让gdb给我任何有用的信息(例如跟踪)，但是我不确定我是否真的知道如何正确使用它.当我尝试使用"LLDB"调试器时，Xcode崩溃了(自从我开始使用它以来，这就是一个常见的主题).

I can't get gdb to give me any useful info after that (like a trace), but I'm not sure I really know how to use it properly. When I try to use the "LLDB" debugger Xcode just crashes (which has been a common theme since I started using it).

我的程序是确定性的，但是当我尝试通过打印语句隔离问题时，行为将发生变化.例如，如果我在某一点添加cout << "hello";，则段错误将消失.其他打印语句导致我的程序在其主循环的不同迭代中出现段错误.而且自然而然地，当我输入足够多的打印语句来精确定位有问题的代码时，该段错误似乎发生在一行之后但下一行之前(即无处).

My program is deterministic, but when I try to isolate the problem with print statements the behavior will change. For example if I add cout << "hello"; at one point the segfault goes away. Other print statements cause my program to segfault in a different iteration of its main loop. And naturally when I put in enough print statements to supposedly pinpoint the offending code, the segfault seems to occur after one line but before the next (i.e. nowhere).

我正在使用指针和动态内存分配，这很可能是问题的原因，但是由于我无法缩小导致错误的代码块的范围，因此我不知道在这里显示什么代码.

I am using pointers and dynamic memory allocation, which is likely the cause of the problem, but since I can't narrow down the block of code causing the error I don't know what code to show here.

我尝试使用Instruments中的泄漏"工具进行性能分析，但没有发现任何泄漏.

I tried profiling with the "Leaks" tool in Instruments, but it didn't find any leaks.

有什么建议吗?我对调试非常缺乏经验，因此确实可以帮上任何忙.

Any advice? I am very inexperienced with debugging so anything would help, really.

已解决.给定某些输入，我的程序将尝试读取数组末尾的内容.

Solved. Given certain inputs, my program would try to read past the end of an array.

推荐答案

我认为没有足够的信息可以帮助您解决DWARF问题.我对该工具链还不够熟悉，无法知道它的健壮性.

I don't think there's enough information that I can help you with the DWARF issue. I am not familiar enough with that toolchain to know how robust it is.

但是，您崩溃的症状闻起来很像堆损坏.我不知道默认情况下OSX会使用什么分配器，但是常见的优化是将元数据与对象内联存储和/或将空列表通过空对象进行存储，这使它们对堆上的缓冲区溢出非常敏感.两次释放一个对象或使用一个悬空的指针(一个已经释放但其空间现在可能已被另一个分配使用的指针)也可能导致看似不确定的且难以跟踪的错误，因为堆的布局可能会在运行.打印语句还使用分配器，这意味着更改打印语句可以在问题出现的时间和地点进行更改.

Your crashing symptoms however smell a lot like heap corruption. I don't know what allocator OSX uses by default, but common optimizations store metadata inline with objects and/or thread the freelist through empty objects, which makes them very sensitive to buffer overflows on the heap. Freeing an object twice or using a dangling pointer (a pointer that has been freed but whose space may now be in use by another allocation) can also cause seemingly nondeterministic and hard to track errors, since the layout of the heap is likely to change between runs. Print statements also use the allocator, which means changing the print statements can change when and where the problem will appear.

您发现可能有用的一种工具，它可以确定这是堆问题还是无关的东西，我的顾问称其为DieHard堆替换(

A tool that you may find helpful in determining if this is a heap problem or something unrelated is a heap replacement called DieHard by my advisor (http://prisms.cs.umass.edu/emery/index.php?page=download-diehard). I believe it will build on OSX, and you can link it into your program using LD_PRELOAD=/path/to/libdiehard.so to replace the default allocator at runtime. Its sole purpose is to resist memory errors and heap corruption, so if your application actually runs with it, that's probably where you need to look.

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