WOW64 Win32 DebugAPI CLR application startup change

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Back in October 2007 I sumarised my findings from getting my Win32 DebugAPI based debug engine working on x64. One of the strange things that I found at the time was this:

When running a CLR app under the Win32 debug interface you only ever seem to hit the native entry point if you're running under WOW64. In all other situations you don't hit the native entry point ever. If you rely on it to pause your debug tools once the process is completely loaded and ready to roll then you need to stick a break point in _CorExeMain in mscoree.dll. What's more, if you're on x64 you might not even be able to access the native entry point's memory...

Well, that seems to have changed... Upon running up my "Debug Tools" test harness a couple of days ago I found I had some test failures when launching CLR 1.0 apps for debug from a Win32 debugger running on an x64 system. On my system only CLR 2.0 apps run as native x64, so, in effect the Win32 debugger was launching a Win32 CLR application whilst running under the WOW64 layer. The behaviour now seems to be identical to running a Win32 CLR application from a Win32 debugger on an x86 system; which, I suppose, is good. The downside is that I've no idea when this change was rolled out and I now have no sure fire way of building a VM box with the old style behaviour to see if I can write some code that works with box fixed and unfixed CLR start up semantics. I guess I can try a clean install of Vista x64...

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