在windbg中调试.Net字符串值

Question

我有一个.Net应用程序转储捕获异常,我正在使用windbg进行分析,并对其中一个方法的String参数值感兴趣.我已经隔离了String对象.我的windbg工作是:

0:000> .loadby sos mscorwks
0:000> !dso
OS Thread Id: 0x16f0 (0)
RSP/REG          Object           Name
00000000001fe908 000000000f011440 System.AppDomainSetup
00000000001fe918 000000000f0335f8 System.ArgumentException
00000000001fe920 000000000f011b60 System.String

0:000> !do 000000000f011b60

Name: System.String
MethodTable: 000007feef477a80
EEClass: 000007feef07e530
Size: 538(0x21a) bytes
 (C:\Windows\assembly\GAC_64\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: C:\Windows\Installer\MSI2D87.tmp
Fields:
              MT    Field   Offset                 Type VT     Attr            Value Name
000007feef47ecf0  4000096        8         System.Int32  1 instance              257 m_arrayLength
000007feef47ecf0  4000097        c         System.Int32  1 instance              179 m_stringLength
000007feef4794c8  4000098       10          System.Char  1 instance               43 m_firstChar
000007feef477a80  4000099       20        System.String  0   shared           static Empty
                                 >> Domain:Value  00000000029d02d0:000000000f011308 <<
000007feef479378  400009a       28        System.Char[]  0   shared           static WhitespaceChars
                                 >> Domain:Value  00000000029d02d0:000000000f0121f8 <<

m_stringLength成员变量表示该字符串长度为179个字符,但检查字符串似乎只有32个字符长.查看此字符串的内存似乎是NULL终止.NULL终止字符后面有更多字符.这可能是重用内存或字符串损坏,但路径看起来正确显示.抛出的异常是"路径中的非法字符",但此路径中没有非法字符.所以此异常的调用堆栈是:

0:000> !CLRStack
OS Thread Id: 0xbac (0)
Child-SP         RetAddr          Call Site
000000000021e9a0 000007feeea64dec System.IO.Path.CheckInvalidPathChars(System.String)
000000000021e9e0 000007feee9c0e66 System.IO.Path.NormalizePathFast(System.String, Boolean)
000000000021eaa0 000007feee9badf8 System.AppDomainSetup.NormalizePath(System.String, Boolean)
000000000021eb10 000007feeea630ad System.AppDomainSetup.SetupDefaultApplicationBase(System.String)
000000000021eb70 000007feee9bb27b System.AppDomain.SetupFusionStore(System.AppDomainSetup)
000000000021ebc0 000007feef87d4a2 System.AppDomain.SetupDomain(Boolean, System.String, System.String)

System.IO.Path.CheckInvalidPathChars方法是否使用m_stringLength中找到的长度处理字符串,还是考虑到字符串本身中的NULL终止？如果你能发现我没有发现的东西,我也会接受这样的事实.

Answer 1

我会将内存中的实际字符串转储到文件中以检查内容,而不是仅仅查看windbg中的输出.

这是我写回来的一个Windbg脚本,将字符串转储到文件中.

$$ Dumps the managed strings to a file
$$ Platform x86
$$ Usage $$>a<"c:\temp\dumpstringtofolder.txt" 6544f9ac 5000 c:\temp\stringtest
$$ First argument is the string method table pointer
$$ Second argument is the Min size of the string that needs to be used filter the strings
$$ Third is the path of the file
.foreach ($string {!dumpheap -short -mt ${$arg1}  -min ${$arg2}})
{ 

  $$ MT        Field      Offset               Type  VT     Attr    Value Name
  $$ 65452978  40000ed        4         System.Int32  1 instance    71117 m_stringLength
  $$ 65451dc8  40000ee        8          System.Char  1 instance       3c m_firstChar
  $$ 6544f9ac  40000ef        8        System.String  0   shared   static Empty

  $$ start of string is stored in the 8th offset, which can be inferred from above
  $$ Size of the string which is stored in the 4th offset
  r@$t0=  poi(${$string}+4)*2
  .writemem ${$arg3}${$string}.txt ${$string}+8 ${$string}+8+@$t0
}

整个想法是使用该.writemem命令将内容转储到文件中.

转储的内容将采用Unicode格式,并使用类似的内容查看其内容

Console.WriteLine(ASCIIEncoding.Unicode.GetString(File.ReadAllBytes(@"c:\temp\stringtest03575270.txt")));

HTH

Answer 2

这是 System.IO.Path.CheckInvalidPathChars 所做的事情（至少在 .NET 2.0 中）：

for (int i = 0; i < path.Length; i++)
{
    int num2 = path[i];
    if (((num2 == 0x22) || (num2 == 60)) || (((num2 == 0x3e) || (num2 == 0x7c)) || (num2 < 0x20)))
    {
        throw new ArgumentException(Environment.GetResourceString("Argument_InvalidPathChars"));
    }
}

请注意，string.Length 中有趣的部分（即 string 如何实际公开其 length 属性）缺失了：

public int Length { [MethodImpl(MethodImplOptions.InternalCall)] get; }

如果可能的话，我会尝试通过检索确切的字符串（最多存储在 m_stringLength 中的长度）并尝试重现该问题来模拟该问题。