I am trying the use of ".local" at the bottom of this:

https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-redirection

My application is called pdptest.exe so I created a dummy
text file called pdptest.exe.local

I wanted it to use my own msvcrt.dll in the same directory.

Nothing happened - it still used the normal one provided
by Windows 10.

Then I recompiled pdptest.exe - and voila, it worked - ie
it executed my msvcrt.dll when I ran pdptest.

Then I created another directory and copied pdptest.exe,
pdptest.exe.local and msvcrt.dll to it.

It didn't work - ie it went to the Windows-provided one.

Any idea what is happening?

Although that's still not what I want.

What I would like to be able to do is have my existing
unchanged executables that depend on msvcrt.dll and
that I have put into my c:\winpath execute an msvcrt.dll
from a specified directory, or follow the PATH variable
or some other variable. Or even if they execute an
msvcrt.dll that is in c:\winpath, that would also be ok.

I don't want to create a ".local" dummy file for every
single one of my executables. Nor do I want to change
any of my executables.

Any idea how to do that?

BTW, I wasn't able to rename msvcrt.dll to msvcrt.dxx
in c:\windows\syswow64 so that I could put in my own.

I really want different windows to be able to have a
different PATH variable, so normally syswow64 is
right, and default, but I in select windows I can
change my PATH and start getting my own msvcrt.dll
executed, because all the programs I will be running
will work nicely with that one.

I checked knowndlls as described here:

https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order

and msvcrt is on the list.

Maybe I need to delete that?

Thanks. Paul.

On Mon, 17 Jul 2023 09:39:16 -0700 (PDT), muta...@gmail.com wrote:
> I am trying the use of ".local" at the bottom of this:
>
> https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-redirection
>
> My application is called pdptest.exe so I created a dummy
> text file called pdptest.exe.local
>
> I wanted it to use my own msvcrt.dll in the same directory.
>
> Nothing happened - it still used the normal one provided
> by Windows 10.
>
> Then I recompiled pdptest.exe - and voila, it worked - ie
> it executed my msvcrt.dll when I ran pdptest.
>
> Then I created another directory and copied pdptest.exe,
> pdptest.exe.local and msvcrt.dll to it.
>
> It didn't work - ie it went to the Windows-provided one.
>
> Any idea what is happening?
>
> Although that's still not what I want.
>
> What I would like to be able to do is have my existing
> unchanged executables that depend on msvcrt.dll and
> that I have put into my c:\winpath execute an msvcrt.dll
> from a specified directory, or follow the PATH variable
> or some other variable. Or even if they execute an
> msvcrt.dll that is in c:\winpath, that would also be ok.
>
> I don't want to create a ".local" dummy file for every
> single one of my executables. Nor do I want to change
> any of my executables.
>
> Any idea how to do that?
>
> BTW, I wasn't able to rename msvcrt.dll to msvcrt.dxx
> in c:\windows\syswow64 so that I could put in my own.
>
> I really want different windows to be able to have a
> different PATH variable, so normally syswow64 is
> right, and default, but I in select windows I can
> change my PATH and start getting my own msvcrt.dll
> executed, because all the programs I will be running
> will work nicely with that one.
>
> I checked knowndlls as described here:
>
> https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order
>
> and msvcrt is on the list.
>
> Maybe I need to delete that?
>
> Thanks. Paul.

If I understand it correctly, the priority of things which affect the DLL
loading is:

1. Application bitness. i.e. 32-bit or 64-bit.

2. Application manifest.

3. DLL redirection.

4. Safe DLL search mode.

5. DLL search order.