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<== Date ==> <== Thread ==>

Subject: RE: How to debug an IOC running on MSWindows using windbg
From: Ahed Aladwan <>
To: "" <>, "" <>
Date: Thu, 1 Nov 2012 17:56:17 +1100

Thanks Paul for sharing that.

I want to add a couple of commands that I believe are very useful especially when debugging exceptions:


1-      k, will show the call stack

2-      !analyze –v, this will do an exception analysis by tracing down which part of your application/windows stack is throwing an exception.

3-      !teb, will show the  raw stack data, with the stack base/limit  address

4-      dds 0xXXXX, will list all the content of an address, try to look into the stack base/limit address range.


Some of the most difficult problems usually originating from access violation exceptions, having DLL’s without pdp’s or symbols servers makes life much harder figuring out which calls are causing the problem instead of dealing with an address.


In addition to WinDbg, tools like depends, dllexp are very handy in showing the hierarchy of needed DLL’s for an executable and listing all the symbols within them.



Ahed Aladwan | Controls Engineering – Imaging & Medical Beamline | Australian Synchrotron
p: (03) 8540 4289 | f: (03) 8540 4200 |
800 Blackburn Road, Clayton, Victoria 3168






From: [] On Behalf Of
Sent: Thursday, 1 November 2012 2:53 AM
Subject: How to debug an IOC running on MSWindows using windbg



The following is a list of instructions to allow debugging of an EPICS IOC on Windows using the Microsoft Windows Debugger (WinDbg).

I have little development experience of EPICS but medium experience of windbg. On hearing that people were experiencing problems debugging iocs on Windows I

decided to check it out.



Brief Introduction to Windows Debugger and comparison with Visual Studio


WinDbg provides a user interface to the underlying debugging engine called Windows Debugger which is implemented in dbgeng.dll. Other interfaces to this engine exist which collectively are called Windows Debuggers. Note that the Visual Studio debugger is completely different to the Windows debugger; however it is possible to integrate use of the Windows Debugger within Visual Studio in Windows 7 and later.

For more information see the documentation in the Windows SDK.


Brief Introduction to winDbg


Microsoft Windows Debugger (WinDbg) is a powerful Windows-based debugger that is capable of both user-mode and kernel-mode debugging. WinDbg provides debugging for the Windows kernel, kernel-mode drivers, and system services, as well as user-mode applications and drivers.


WinDbg uses the Visual Studio debug symbol formats for source-level debugging. It can access any symbol or variable from a module that has PDB symbol files, and can access any public function's name that is exposed by modules that were compiled with COFF symbol files (such as Windows .dbg files). WinDbg can view source code, set breakpoints, view variables (including C++ objects), stack traces, and memory. Its Debugger Command window allows the user to issue a wide variety of commands. For kernel-mode debugging, WinDbg typically requires two computers (the host computer and the target computer). WinDbg also supports various remote debugging options for both user-mode and kernel-mode targets.


WinDbg is a graphical-interface counterpart to CDB/NTSD and to KD/NTKD.


Building EPICS base, an IOC and symbol files


1. Download and build EPICS base.

Simply follow the existing instructions on the ANL EPICS Windows page(, including the additional instructions

posted by Carsten Winkler.(


I choose to use:

Visual C++ 2010 Express



GnuWin 3.8.1


Note that I set EPICS_HOST_ARCH=win32-x86 although the OS is Windows 64bit.



2. Build the example ioc

a)Follow the instructions in the Application Developer Guide section 2.2.2 (

mkdir c:\ioc1

cd c:\ioc1

c:\base-3.14.12\bin\win32-x86\ -t example myexample

c:\base-3.14.12\bin\win32-x86\ -i -t example myexample


b) Add compiler and linker flags to build a PDB symbol file.

I added the following statements in <top>\configure\CONFIG. e.g. c:\ioc1\configure\CONFIG







I expect someone with better knowledge of the EPICS build system could suggest a better method to add these flags.


c) Compile and link

cd c:\ioc1



Start the IOC


Just follow the instructions in Application Developer Guide section 2.2.7


c:\ioc1>cd iocBoot\iocmyexample

c:\ioc1\iocBoot\iocmyexample>..\..\bin\win32-x86\myexample.exe st.cmd

epics> dbl   (note that name of the machine is paulgibbonsHost, this will be replaced by the name of your machine )





















Test the ioc

C:\Users\paul gibbons>caget paulgibbonsHost:ai1

paulgibbonsHost:ai1            5




Install and start Windbg


Download and install the Windows SDK. Note that you only need the Debugging Tools.

Start windbg from the newly created Windows Kits in the Start menu.


Attaching windbg to a process and stepping through code


Use File | Attach to a Process.. and select the ioc process. In the example above the process is called myexample.exe

Note that the process is interrupted by this action. To continue execution use menu Debug | Go.


To control the debugger first interrupted execution of the process using command Debug | Break.

To view the loaded modules (exe, dll) use the command lm

To load the symbol file for a module for which the loading of symbols is shown as deferred enter the command >ld <module> e.g. >ld myexampleSupport

To view all the symbols of the module myexampleSupport enter the command >x myexampleSupport!*


If the function on which you wish to set a break point is viewable by the x command then you can set a breakpoint using the command>bpx <address>


In this example we will set a breakpoint on the function process defined in C:\ioc1\myexampleApp\src\xxxRecord.c which is built into the module myexampleSupport.dll

>bp myexampleSupport!process


Now continue execution of the ioc using Debug | Go.


xxxRecord defines the record type xxx, of which the PV paulgibbonsHost:xxxExample is an instance. So to cause the breakpoint to be fired we simple do a caput on this record

>caput paulgibbonsHost:xxxExample 1


On detection of the breakpoint windbg will open the relevant source file at which point you can view variables and step through code.


Note that we have not had to tell windbg where to find the symbol file (pdb) or source code as it is in the position recorded in the executable module. You can however tell

windebg where to find these using the commands:

File | Symbol File Path to specify the path in which to search for symbol files. In this example C:\ioc1\myexampleApp\src\O.win32-x86

File | Source File Path to specify the path in which to search for source files. In this example C:\ioc1\myexampleApp\src








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How to debug an IOC running on MSWindows using windbg Paul.gibbons

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