WinDbg and SoS, how do I print/dump a large string?

Question

I am debugging a hangdump coming from a production server using WinDbg with the SoS extension.

There is a string parameter in one of the stacks, that I need to know the value of. However, it is a rather large string, and WinDbg won't print it when I am using DumpObj. This is the output from DumpObj:

0:036> !do 00000001b30d8668
Name: System.String
MethodTable: 0000064278436728
EEClass: 000006427803e520
Size: 5125300(0x4e34b4) bytes
 (C:\WINDOWS\assembly\GAC_64\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: <String is invalid or too large to print>

Fields:
              MT    Field   Offset                 Type VT     Attr            Value Name
000006427843d998  4000096        8         System.Int32  1 instance          2562638 m_arrayLength
000006427843d998  4000097        c         System.Int32  1 instance          2562637 m_stringLength
0000064278438170  4000098       10          System.Char  1 instance               3c m_firstChar
0000064278436728  4000099       20        System.String  0   shared           static Empty
                                 >> Domain:Value  0000000000163260:000000007fff0370 00000000001a6760:000000007fff0370 <<
0000064278438020  400009a       28        System.Char[]  0   shared           static WhitespaceChars
                                 >> Domain:Value  0000000000163260:000000007fff0b60 00000000001a6760:000000007fff89f0 <<

How can I get the value of this string instance ? Preferably dumped to a file.

Answer 1

Here is a script I wrote to dump strings to a file within windbg.

$$ Dumps the managed strings to a file
$$ 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
}

and this is how it can be used$$>a<”c:\temp\dumpstringtofolder.txt” 6544f9ac 5000 c:\temp\stringtest

The dumped contents would be in Unicode format and to view its contents use something like this Console.WriteLine(ASCIIEncoding.Unicode.GetString(File.ReadAllBytes(@"c:\temp\stringtest03575270.txt")));

HTH