Thursday, July 07, 2005

Setting breakpoints when production servers have no access to symbols

In some cases a production server may not

  1. Have access to the internet to use the Microsoft symbol server.
  2. Access to symbol files using a UNC path.

In both cases it is impossible to set break points using symbolic names in either a live debug session or when using adplus. This is clearly a problem for the adplus configuration script I discussed in VB Script production debugging.

If symbols aren’t available there is another solution by adding break points set using a memory address location. In the previous blog the adplus config file was setting a breakpoint on the function vbscript!CScriptRuntime::RecordErrorContext. To find out the memory address for the breakpoint we need to determine what the offset to vbscript!CScriptRuntime::RecordErrorContext is in vbscript.dll.

First we need to take a dump of the process on the production server and load it into windbg on a machine which does have access to a symbol store. Open the dump and enter the x command to find the address of the function

0:031> x vbscript!CScriptRuntime::RecordErrorContext
734753cf vbscript!CScriptRuntime::RecordErrorContext =

Then we need to find the module address for vbscript.

0:031> lmm vbscript
start end module name
73460000 734c5000 vbscript

Subtract the module start address from the symbol address

0:031> ?734753cf - 73460000
Evaluate expression: 86991 = 000153cf

Now we have our offset we can use it to set a break point either during a live debug or in the adplus config file. The dump I used in the example above was using of vbscript.dll. The Address element of the adplus configuration file should be modified from



vbscript + 0x000153cf

Sunday, July 03, 2005

Effective Production Debugging MSDN Article

Following my recent production debugging MSDN article (
I've written a number of posts on techniques I wanted to cover in the article but couldn't as I ran out of space.

I've already written on topics such as creating dumps through terminal services and VB Script debugging however If there's anything you'd especially like to see let me know and I'll try and cover it.