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Re: Providing cygwin1.dll in both 32- and 64-bit versions






Hans-Bernhard Bröker skrev:
Am 03.02.2017 um 12:49 schrieb Thomas Nilefalk:
Hans-Bernhard Bröker skrev:
Am 02.02.2017 um 22:12 schrieb Thomas Nilefalk:

'how can I make a 32-bit compiled cygwin program run under cygwin64'?

You can't. Nor can anybody else. For a Cygwin64-based program,
Cygwin32 is a bona fide cross-compilation platform rather than just
some subset of the same platform. The same holds vice versa.

What triggered this chain of thought was that running an exe
cross-compiled to 32-bit just silently failed.

BTDT, and can feel your pain.

It would have helped me at that time if I would have gotten an error
message from the dynamic loader, like on other platforms ("skipping
cygwin1.dll because it has the wrong architecture").

Welcome to one of the deeper levels of the tragedy (or comedy of
errors...) commonly known as Windows "DLL hell". AFAIK there is no
dynamic loader Cygwin would have any amount of control over. This fails
before any part of Cygwin ever gets loaded, so there's practically
nothing cygwin can do about it.

Anyways, thanks for the explanation. Given that, the solution for runnig
32-bit cygwin programs on cygwin64 is of course

$ PATH=<path_to_32-bit_cygwin1.dll>:$PATH
<32-bit_cross_compiled_program>

Actually that's not the solution, either. It's an unreliable workaround
at best. That's because after this, all 64-bit cygwin programs executed
by your own program will fail to start because they get the wrong Cygwin
DLL.

The solution is to have a Cygwin32 environment installed independently
of Cygwin64, and keep each executable strictly in its own environment.
Mixing the two causes nothing but problems.


Emperical data suggests that:

> Thomas@thoni64:[x86_64] ~/Utveckling/ToolMaker
> $ file bin/pmk
> bin/pmk: PE32 executable (console) Intel 80386, for MS Windows
>
> Thomas@thoni64:[x86_64] ~/Utveckling/ToolMaker
> $ bin/pmk
>
> Thomas@thoni64:[x86_64] ~/Utveckling/ToolMaker
> $ PATH=/cygdrive/c/cygwin32/bin:$PATH bin/pmk
> Usage: /cygdrive/c/Users/Thomas/Utveckling/ToolMaker/bin/pmk [-help [options] <input file>
>
> Thomas@thoni64:[x86_64] ~/Utveckling/ToolMaker
> $ PATH=$PATH:/cygdrive/c/cygwin32/bin bin/pmk
> Usage: /cygdrive/c/Users/Thomas/Utveckling/ToolMaker/bin/pmk [-help] [options] <input file>

The first run is evidence that on an x86_64, running a 32-bit exe silently exits. But note that adding the 32-bit cygwin1.dll to the path, even at the end like in the last command, will allow the loader to find that instead of the 64-bit one.

This is good news because it allows you to, at least in some cases, run 32-bit cygwin-dependent programs in a 64-bit Cygwin.

Although as you say, mixing the environments in a more general sense, would probably mostly cause confusion because of other issues, like non-cygwin-DLL:s (which would need similar treatment) and other shared, but not equal, resources from the two environments.

The other way around does not seem to work, though. So it seems that you can't run 64-bit cygwin-dependent exes in a 32-bit environment by adding the 64-bit cygwin1.dll to the path. Which kind of makes sense, given backwards compatibility thinking.

I'm happy because my discovery solves my particular need (which is not generally mixing 32 and 64-bit environments). Maybe someone else can benefit from this. Although I am definitely not assuming this is by design (it might be, you never know what MS actually are thinking) and will not rely on it working for the future.

Regards,
    Thomas

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