历史经验之仅通过崩溃地址找出源代码的出错行

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整理日期：2005年12月7日

作为程序员，我们平时最担心见到的事情是什么？是内存泄漏？是界面不好看？……错啦！我相信我的看法是不会有人反对的——那就是，程序发生了崩溃！

“该程序执行了非法操作，即将关闭。请与你的软件供应商联系。”，呵呵，这句 M$ 的“名言”，恐怕就是程序员最担心见到的东西了。有的时候，自己的程序在自己的机器上运行得好好的，但是到了别人的机器上就崩溃了；有时自己在编写和测试的过程中就莫名其妙地遇到了非法操作，但是却无法确定到底是源代码中的哪行引起的……是不是很痛苦呢？不要紧，本文可以帮助你走出这种困境，甚至你从此之后可以自豪地要求用户把崩溃地址告诉你，然后你就可以精确地定位到源代码中出错的那行了。（很神奇吧？呵呵。）

首先我必须强调的是，本方法可以在目前市面上任意一款编译器上面使用。但是我只熟悉 M$ 的 VC 和 MASM ，因此后面的部分只介绍如何在这两个编译器中实现，请读者自行融会贯通，掌握在别的编译器上使用的方法。

Well，废话说完了，让我们开始！ ：）

首先必须生成程序的 MAP 文件。什么是 MAP 文件？简单地讲， MAP 文件是程序的全局符号、源文件和代码行号信息的唯一的文本表示方法，它可以在任何地方、任何时候使用，不需要有额外的程序进行支持。而且，这是唯一能找出程序崩溃的地方的救星。

好吧，既然 MAP 文件如此神奇，那么我们应该如何生成它呢？在 VC 中，我们可以按下 Alt+F7 ，打开“Project Settings”选项页，选择 C/C++ 选项卡，并在最下面的 Project Options 里面输入：/Zd ，然后要选择 Link 选项卡，在最下面的 Project Options 里面输入： /mapinfo:lines 和 /map:PROJECT_NAME.map 。最后按下 F7 来编译生成 EXE 可执行文件和 MAP 文件。

在 MASM 中，我们要设置编译和连接参数，我通常是这样做的：
rc %1.rc
ml /c /coff /Zd %1.asm
link /subsystem:windows /mapinfo:exports /mapinfo:lines /map:%1.map %1.obj %1.res

把它保存成 makem.bat ，就可以在命令行输入 makem filename 来编译生成 EXE 可执行文件和 MAP 文件了。

在此我先解释一下加入的参数的含义：
/Zd 表示在编译的时候生成行信息
/map[:filename] 表示生成 MAP 文件的路径和文件名
/mapinfo:lines 表示生成 MAP 文件时，加入行信息
/mapinfo:exports 表示生成 MAP 文件时，加入 exported functions （如果生成的是 DLL 文件，这个选项就要加上）

OK，通过上面的步骤，我们已经得到了 MAP 文件，那么我们该如何利用它呢？

让我们从简单的实例入手，请打开你的 VC ，新建这样一个文件：

1  
2  void Crash(void)
3  {
4      int i = 1;
5      int j = 0;
6      i /= j;
7  }
8  
9  void main(void)
10  {
11      Crash();
12  }

很显然本程序有“除0错误”，在 Debug 方式下编译的话，运行时肯定会产生“非法操作”。好，让我们运行它，果然，“非法操作”对话框出现了，这时我们点击“详细信息”按钮，记录下产生崩溃的地址——在我的机器上是 0x0040104a 。

再看看它的 MAP 文件：（由于文件内容太长，中间没用的部分我进行了省略）
CrashDemo

Timestamp is 3e430a76 (Fri Feb 07 09:23:02 2003)

Preferred load address is 00400000

Start Length Name Class
0001:00000000 0000de04H .text CODE
0001:0000de04 0001000cH .textbss CODE
0002:00000000 00001346H .rdata DATA
0002:00001346 00000000H .edata DATA
0003:00000000 00000104H .CRT X C A D A T A 0003 : 0000010400000104 H . C R T XCA DATA 0003:00000104 00000104H .CRT XCADATA0003:0000010400000104H.CRTXCZ DATA
0003:00000208 00000104H .CRT X I A D A T A 0003 : 0000030 c 00000109 H . C R T XIA DATA 0003:0000030c 00000109H .CRT XIADATA0003:0000030c00000109H.CRTXIC DATA
0003:00000418 00000104H .CRT X I Z D A T A 0003 : 0000051 c 00000104 H . C R T XIZ DATA 0003:0000051c 00000104H .CRT XIZDATA0003:0000051c00000104H.CRTXPA DATA
0003:00000620 00000104H .CRT X P X D A T A 0003 : 0000072400000104 H . C R T XPX DATA 0003:00000724 00000104H .CRT XPXDATA0003:0000072400000104H.CRTXPZ DATA
0003:00000828 00000104H .CRT X T A D A T A 0003 : 0000092 c 00000104 H . C R T XTA DATA 0003:0000092c 00000104H .CRT XTADATA0003:0000092c00000104H.CRTXTZ DATA
0003:00000a30 00000b93H .data DATA
0003:000015c4 00001974H .bss DATA
0004:00000000 00000014H .idata$2 DATA
0004:00000014 00000014H .idata$3 DATA
0004:00000028 00000110H .idata$4 DATA
0004:00000138 00000110H .idata$5 DATA
0004:00000248 000004afH .idata$6 DATA

Address Publics by Value Rva+Base Lib:Object

0001:00000020 ?Crash@@YAXXZ 00401020 f CrashDemo.obj
0001:00000070 _main 00401070 f CrashDemo.obj
0004:00000000 __IMPORT_DESCRIPTOR_KERNEL32 00424000 kernel32:KERNEL32.dll
0004:00000014 __NULL_IMPORT_DESCRIPTOR 00424014 kernel32:KERNEL32.dll
0004:00000138 __imp__GetCommandLineA@0 00424138 kernel32:KERNEL32.dll
0004:0000013c __imp__GetVersion@0 0042413c kernel32:KERNEL32.dll
0004:00000140 __imp__ExitProcess@4 00424140 kernel32:KERNEL32.dll
0004:00000144 __imp__DebugBreak@0 00424144 kernel32:KERNEL32.dll
0004:00000148 __imp__GetStdHandle@4 00424148 kernel32:KERNEL32.dll
0004:0000014c __imp__WriteFile@20 0042414c kernel32:KERNEL32.dll
0004:00000150 __imp__InterlockedDecrement@4 00424150 kernel32:KERNEL32.dll
0004:00000154 __imp__OutputDebugStringA@4 00424154 kernel32:KERNEL32.dll
0004:00000158 __imp__GetProcAddress@8 00424158 kernel32:KERNEL32.dll
0004:0000015c __imp__LoadLibraryA@4 0042415c kernel32:KERNEL32.dll
0004:00000160 __imp__InterlockedIncrement@4 00424160 kernel32:KERNEL32.dll
0004:00000164 __imp__GetModuleFileNameA@12 00424164 kernel32:KERNEL32.dll
0004:00000168 __imp__TerminateProcess@8 00424168 kernel32:KERNEL32.dll
0004:0000016c __imp__GetCurrentProcess@0 0042416c kernel32:KERNEL32.dll
0004:00000170 __imp__UnhandledExceptionFilter@4 00424170 kernel32:KERNEL32.dll
0004:00000174 __imp__FreeEnvironmentStringsA@4 00424174 kernel32:KERNEL32.dll
0004:00000178 __imp__FreeEnvironmentStringsW@4 00424178 kernel32:KERNEL32.dll
0004:0000017c __imp__WideCharToMultiByte@32 0042417c kernel32:KERNEL32.dll
0004:00000180 __imp__GetEnvironmentStrings@0 00424180 kernel32:KERNEL32.dll
0004:00000184 __imp__GetEnvironmentStringsW@0 00424184 kernel32:KERNEL32.dll
0004:00000188 __imp__SetHandleCount@4 00424188 kernel32:KERNEL32.dll
0004:0000018c __imp__GetFileType@4 0042418c kernel32:KERNEL32.dll
0004:00000190 __imp__GetStartupInfoA@4 00424190 kernel32:KERNEL32.dll
0004:00000194 __imp__HeapDestroy@4 00424194 kernel32:KERNEL32.dll
0004:00000198 __imp__HeapCreate@12 00424198 kernel32:KERNEL32.dll
0004:0000019c __imp__HeapFree@12 0042419c kernel32:KERNEL32.dll
0004:000001a0 __imp__VirtualFree@12 004241a0 kernel32:KERNEL32.dll
0004:000001a4 __imp__RtlUnwind@16 004241a4 kernel32:KERNEL32.dll
0004:000001a8 __imp__GetLastError@0 004241a8 kernel32:KERNEL32.dll
0004:000001ac __imp__SetConsoleCtrlHandler@8 004241ac kernel32:KERNEL32.dll
0004:000001b0 __imp__IsBadWritePtr@8 004241b0 kernel32:KERNEL32.dll
0004:000001b4 __imp__IsBadReadPtr@8 004241b4 kernel32:KERNEL32.dll
0004:000001b8 __imp__HeapValidate@12 004241b8 kernel32:KERNEL32.dll
0004:000001bc __imp__GetCPInfo@8 004241bc kernel32:KERNEL32.dll
0004:000001c0 __imp__GetACP@0 004241c0 kernel32:KERNEL32.dll
0004:000001c4 __imp__GetOEMCP@0 004241c4 kernel32:KERNEL32.dll
0004:000001c8 __imp__HeapAlloc@12 004241c8 kernel32:KERNEL32.dll
0004:000001cc __imp__VirtualAlloc@16 004241cc kernel32:KERNEL32.dll
0004:000001d0 __imp__HeapReAlloc@16 004241d0 kernel32:KERNEL32.dll
0004:000001d4 __imp__MultiByteToWideChar@24 004241d4 kernel32:KERNEL32.dll
0004:000001d8 __imp__LCMapStringA@24 004241d8 kernel32:KERNEL32.dll
0004:000001dc __imp__LCMapStringW@24 004241dc kernel32:KERNEL32.dll
0004:000001e0 __imp__GetStringTypeA@20 004241e0 kernel32:KERNEL32.dll
0004:000001e4 __imp__GetStringTypeW@16 004241e4 kernel32:KERNEL32.dll
0004:000001e8 __imp__SetFilePointer@16 004241e8 kernel32:KERNEL32.dll
0004:000001ec __imp__SetStdHandle@8 004241ec kernel32:KERNEL32.dll
0004:000001f0 __imp__FlushFileBuffers@4 004241f0 kernel32:KERNEL32.dll
0004:000001f4 __imp__CloseHandle@4 004241f4 kernel32:KERNEL32.dll
0004:000001f8 \177KERNEL32_NULL_THUNK_DATA 004241f8 kernel32:KERNEL32.dll

entry point at 0001:000000f0

Line numbers for .\Debug\CrashDemo.obj(d:\msdev\myprojects\crashdemo\crashdemo.cpp) segment .text

13 0001:00000020 14 0001:00000038 15 0001:0000003f 16 0001:00000046
17 0001:00000050 20 0001:00000070 21 0001:00000088 22 0001:0000008d

如果仔细浏览 Rva+Base 这栏，你会发现第一个比崩溃地址 0x0040104a 大的函数地址是 0x00401070 ，所以在 0x00401070 这个地址之前的那个入口就是产生崩溃的函数，也就是这行：
0001:00000020 ?Crash@@YAXXZ 00401020 f CrashDemo.obj

因此，发生崩溃的函数就是 ?Crash@@YAXXZ ，所有以问号开头的函数名称都是 C++ 修饰的名称。在我们的源程序中，也就是 Crash() 这个子函数。

OK，现在我们轻而易举地便知道了发生崩溃的函数名称，你是不是很兴奋呢？呵呵，先别忙，接下来，更厉害的招数要出场了。

请注意 MAP 文件的最后部分——代码行信息（Line numbers information），它是以这样的形式显示的：
13 0001:00000020

第一个数字代表在源代码中的代码行号，第二个数是该代码行在所属的代码段中的偏移量。

如果要查找代码行号，需要使用下面的公式做一些十六进制的减法运算：
崩溃行偏移 = 崩溃地址（Crash Address） - 基地址（ImageBase Address） - 0x1000

为什么要这样做呢？细心的朋友可能会留意到 Rva+Base 这栏了，我们得到的崩溃地址都是由 偏移地址（Rva）+ 基地址（Base） 得来的，所以在计算行号的时候要把基地址减去，一般情况下，基地址的值是 0x00400000 。另外，由于一般的 PE 文件的代码段都是从 0x1000 偏移开始的，所以也必须减去 0x1000 。

好了，明白了这点，我们就可以来进行小学减法计算了：
崩溃行偏移 = 0x0040104a - 0x00400000 - 0x1000 = 0x4a

如果浏览 MAP 文件的代码行信息，会看到不超过计算结果，但却最接近的数是 CrashDemo.cpp 文件中的：
16 0001:00000046

也就是在源代码中的第 16 行，让我们来看看源代码:
16 i /= j;

哈！！！果然就是第 16 行啊！

兴奋吗？我也一样！ ：）

方法已经介绍完了，从今以后，我们就可以精确地定位到源代码中的崩溃行，而且只要编译器可以生成 MAP 文件（包括 VC、MASM、VB、BCB、Delphi……），本方法都是适用的。我们时常抱怨 M$ 的产品如何如何差，但其实 M$ 还是有意无意间提供了很多有价值的信息给我们的，只是我们往往不懂得怎么利用而已……相信这样一来，你就可以更为从容地面对“非法操作”提示了。你甚至可以要求用户提供崩溃的地址，然后就可以坐在家中舒舒服服地找到出错的那行，并进行修正。

Introduction
Programming neat applications is one thing. But when a user informs you your software has crashed, you know it’s best to fix this before adding other features. If you’re lucky enough, the user will have a crash address. This will go a long way in solving the problem. But how can you determine what went wrong, using this crash address?
Creating a MAP file
Well first of all, you’ll need a MAP file. If you don’t have one, it will be nearly impossible to find where your application crashed using the crash address. So first, I’ll show you how to create a good MAP file. For this, I will create a new project (MAPFILE). You can do the same, or adjust your own project. I create a new project using the Win32 Application option in VC++ 6.0, selecting the ‘typical “Hello Word!” application’ to keep the size of the MAP file reasonable for explanation.
Once created we need to adjust the project settings for the release version. In the C/C++ tab, select “Line Numbers Only” for Debug Info.

Many people forget this, but you’ll need this option if you want a good MAP file. This will not affect your release in any way. Next is the Link tab. Here you need to select the “Generate mapfile” option. Also, type the switches /MAPINFO:LINES and /MAPINFO:EXPORTS in the Project Options edit box.

Now, you’re ready to compile and link your project. After linking, you will find a .map file in your intermediate directory (together with your exe).
Reading the MAP file
After all this dull work, now comes the neat part: how to read the MAP file. We’ll do this by using a crash example. So first: how to crash your application. I did this by adding these two lines at the end of the InitInstance() function:
char* pEmpty = NULL;
*pEmpty = ‘x’; // This is line 119
I’m sure you can find other instructions which will crash your application. Now recompile and link. If you start the application, it will crash and you’ll get a message like this: ‘The instruction at “0x004011a1” referenced memory at “0x00000000”. The memory could not be “Written”.’ .
Now, it’s time to open the MAP file with notepad or something similar. You MAP file will look like this:
The top of the MAP file contains the module name, the timestamp indicating the link of the project, and the preferred load address (which will probably be 0x00400000 unless you’re using a dll). After the header comes the section information that shows which sections the linker brought in from the various OBJ and LIB files.
MAPFILE

Timestamp is 3df6394d (Tue Dec 10 19:58:21 2002)

Preferred load address is 00400000

Start Length Name Class
0001:00000000 000038feH .text CODE
0002:00000000 000000f4H .idata$5 DATA
0002:000000f8 00000394H .rdata DATA
0002:0000048c 00000028H .idata$2 DATA
0002:000004b4 00000014H .idata$3 DATA
0002:000004c8 000000f4H .idata$4 DATA
0002:000005bc 0000040aH .idata 6 D A T A 0002 : 000009 c 600000000 H . e d a t a D A T A 0003 : 0000000000000004 H . C R T 6 DATA 0002:000009c6 00000000H .edata DATA 0003:00000000 00000004H .CRT 6DATA0002:000009c600000000H.edataDATA0003:0000000000000004H.CRTXCA DATA
0003:00000004 00000004H .CRT X C Z D A T A 0003 : 0000000800000004 H . C R T XCZ DATA 0003:00000008 00000004H .CRT XCZDATA0003:0000000800000004H.CRTXIA DATA
0003:0000000c 00000004H .CRT X I C D A T A 0003 : 0000001000000004 H . C R T XIC DATA 0003:00000010 00000004H .CRT XICDATA0003:0000001000000004H.CRTXIZ DATA
0003:00000014 00000004H .CRT X P A D A T A 0003 : 0000001800000004 H . C R T XPA DATA 0003:00000018 00000004H .CRT XPADATA0003:0000001800000004H.CRTXPZ DATA
0003:0000001c 00000004H .CRT X T A D A T A 0003 : 0000002000000004 H . C R T XTA DATA 0003:00000020 00000004H .CRT XTADATA0003:0000002000000004H.CRTXTZ DATA
0003:00000030 00002490H .data DATA
0003:000024c0 000005fcH .bss DATA
0004:00000000 00000250H .rsrc$01 DATA
0004:00000250 00000720H .rsrc$02 DATA
After the section information, you get the public function information. Notice the “public” part. If you have static-declared C functions, they won’t show up in the MAP file. Fortunately, the line numbers will still reflect the static functions. The important parts of the public function information are the function names and the information in the Rva+Base column, which is the starting address of the function.
Address Publics by Value Rva+Base Lib:Object

0001:00000000 WinMain@16 00401000 f MAPFILE.obj
0001:000000c0 ?MyRegisterClass@@YAGPAUHINSTANCE_@@@Z 004010c0 f MAPFILE.obj
0001:00000150 ?InitInstance@@YAHPAUHINSTANCE__@@H@Z 00401150 f MAPFILE.obj
0001:000001b0 ?WndProc@@YGJPAUHWND__@@IIJ@Z 004011b0 f MAPFILE.obj
0001:00000310 ?About@@YGJPAUHWND__@@IIJ@Z 00401310 f MAPFILE.obj
0001:00000350 _WinMainCRTStartup 00401350 f LIBC:wincrt0.obj
0001:00000446 __amsg_exit 00401446 f LIBC:wincrt0.obj
0001:0000048f __cinit 0040148f f LIBC:crt0dat.obj
0001:000004bc _exit 004014bc f LIBC:crt0dat.obj
0001:000004cd __exit 004014cd f LIBC:crt0dat.obj
0001:00000591 __XcptFilter 00401591 f LIBC:winxfltr.obj
0001:00000715 __wincmdln 00401715 f LIBC:wincmdln.obj
//SNIPPED FOR BETTER READING
0003:00002ab4 __FPinit 00408ab4
0003:00002ab8 __acmdln 00408ab8

entry point at 0001:00000350

Static symbols

0001:000035d0 LeadUp1 004045d0 f LIBC:memmove.obj
0001:000035fc LeadUp2 004045fc f LIBC:memmove.obj
//SNIPPED FOR BETTER READING
0001:00000577 __initterm 00401577 f LIBC:crt0dat.obj
0001:0000046b _fast_error_exit 0040146b f LIBC:wincrt0.obj
The public function part is followed by the line information (you got this if you used the /MAPINFO:LINES in the Link tab and selected the “Line numbers” in the C/C++ tab). After this, you will get the export information if your project contains exported functions and you included /MAPINFO:EXPORTS in the link tab.
Line numbers for .\Release\MAPFILE.obj(F:\MAPFILE\MAPFILE.cpp) segment .text

24 0001:00000000 30 0001:00000004 31 0001:0000001b 32 0001:00000027
35 0001:0000002d 53 0001:00000041 40 0001:00000047 43 0001:00000050
45 0001:00000077 47 0001:00000088 48 0001:0000008f 52 0001:000000ad
53 0001:000000b3 71 0001:000000c0 80 0001:000000c3 81 0001:000000c8
82 0001:000000ff 86 0001:00000114 88 0001:00000135 89 0001:00000145
102 0001:00000150 108 0001:00000155 110 0001:00000188 122 0001:0000018d
115 0001:0000018e 116 0001:0000019a 119 0001:000001a1 121 0001:000001a8
122 0001:000001ae 135 0001:000001b0 143 0001:000001cc 172 0001:000001ee
175 0001:0000020d 149 0001:00000216 157 0001:0000022c 175 0001:00000248
154 0001:00000251 174 0001:0000025f 175 0001:00000261 151 0001:0000026a
174 0001:00000287 175 0001:00000289 161 0001:00000294 164 0001:000002a8
165 0001:000002b6 166 0001:000002d8 174 0001:000002e7 175 0001:000002e9
169 0001:000002f2 174 0001:000002fa 175 0001:000002fc 179 0001:00000310
186 0001:0000031e 193 0001:0000032e 194 0001:00000330 188 0001:00000333
183 0001:00000344 194 0001:00000349
Now we will look up where the crash occurred. First, we’ll determine which function contains the crash address. Look in the “Rva+Base” column and search the first function with an address bigger than the crash address. The preceding entry in the MAP file is the function that had the crash. In our example our crash address is 0x004011a1. This is between 0x00401150 and 0x004011b0 so we know the crash function is ?InitInstance@@YAHPAUHINSTANCE__@@H@Z . Any function name that starts with a question mark is a C++ decorated name. To translate the name, pass it as a command-line parameter to the Platform SDK program UNDNAME.EXE (in the bin dir). You won’t need to do this most of the time as you might figure it out just by looking at it (here: InitInstance() in MAPFILE.obj).
This is a big step for bug tracking. But it gets even better: we can find out on which line the crash occurred! We need to do some basic hexadecimal mathematics, so people whom can’t do this without a calculator: now is the time to use it. The first step is the following calculation: crash_address - preferred_load_address - 0x1000
Addresses are offsets from the beginning of the first code section, se we need to do this calculation. Subtracting the preferred load address is logical, but why do we need to substract another 0x1000? The crash address is an offset from the beginning of the code section, but the first part of the binary isn’t the code section! The first part of the binary is the Portable Executable (PE), which is 0x1000 bytes long. Mystery solved. In our example, this is: 0x004011a1 - 0x00400000 - 0x1000 = 0x1a1
Now it’s time to look in the line information section of the MAP file. The lines are shown like this: 30 0001:00000004. The first number is the line number, the second number is the offset from the beginning of the code section in which this line occurred. If we want to look for our line number, we just have to do the same thing we did for the function: determine the first occurrence of a bigger offset than the one we just calculated. The crash occurred in the preceding entry. In our example: 0x1a1 is before 0x1a8. So our crash occurred on line 119 in MAPFILE.CPP.
Keeping track of MAP files
Each release had it’s own MAP file. It’s not a bad idea to include the MAP file with the exe distribution. This way, you can be certain you have the correct MAP file for this exe. You could keep every MAP file with every exe on your system, but we all know this might give some troubles later on. The MAP file doesn’t contain any information you wouldn’t want the user to see (unless maybe class and function names ?) . A user would have no use with it, but at least you can ask for the MAP file if you don’t have a copy yourself.
Acknowledgements
John Robbins for his “Debugging Applications” book
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