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Debugging a delayed-load DLL (such as a Python extension) with Eclipse/MinGW

Submitted by keath on Fri, 2009-01-30 12:28

So here's the scenario: you've built a DLL that gets dynamically-loaded at run-time by another application (possibly not yours) and now you want to debug it under Eclipse, but execution blows right past your breakpoints! What to do?

In my case, I'm debugging a Python extension, but this scenario applies to other situations as well - Apache modules, PHP extensions and plug-ins to other applications. In all of these cases the application loads you DLL at some point after it has launched - usually in response to a script or user action. Debugging the DLL in these situations can be challenging because it is not loaded in memory along with the application.

MinGW/MSYS Vista Issues

Submitted by keath on Thu, 2008-12-11 22:46

The MinGW and MSYS environment has a couple of problems under Windows Vista:

First, the install, install-info and patch commands are flagged automatically by Vista as requiring Administrator privileges based simply on their names. Nice. This will cause mysterious permission denied errors during builds. The UAC dialog won't pop up in this case either.

The fix is to add ".manifest" files for each of these commands in the same directory as the command. The manifest file looks something like this:

install.exe.manifest:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
  <assemblyIdentity version="1.0.0.0"
     processorArchitecture="X86"
     name="install.exe"
     type="win32"/>

  <!-- Identify the application security requirements. -->
  <trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
    <security>
      <requestedPrivileges>
        <requestedExecutionLevel
          level="asInvoker"
          uiAccess="false"/>
        </requestedPrivileges>
       </security>
  </trustInfo>
</assembly>

Create and edit one of these for each of the commands above. If you have Cygwin, you can copy them from /cygwin/bin.

The second problem I ran into under Vista is that tar operations on gzipped or bzip2 files will frequently fail with a "child died with signal 13" error. It appears that the MSYS versions of gzip and bzip2 have issues under Vista. I can use the Cygwin versions in their place with no problems. If you're using MSYS to build packages, be careful with having cygwin in your PATH however.