Cross-compile Qt 5.9.1 with MSVC 2017 x64 to x86 fails with linker error

v5exp4 · wrote on 22 Nov 2017, 11:04

AFAIK they are. Still I would like to know what happens, it should be feasible to cross compile Qt from x64 to x86.

v5exp4 · wrote on 24 Nov 2017, 15:42

So far it seems, no matter what I do (tried passing -device-options, creating own mkspec for specific 32 bit platform, not to use the common msvc mkspec), after configuration my target architecture is set to x86_64 in qtbase/mkspecs/qconfig.pri. Also at the configuration phase when running config tests I get the message that target platform is x86_64.

What parameters shall I pass to the configure script to make it change? Has anyone tried this before?

SGaist · 29 Nov 2017, 08:14

Hi,

Did you try the x86 Native Tools Command Prompt ?

Also, how did you setup your build environment for the cross-compilation ?

v5exp4 · 27 Nov 2017, 09:41

Hi,

Thanks for the response!

I might have a conceptional misunderstanding. I have tried to set MSVC to x64 to x86 cross-compilation, thus ran vcvars.bat amd64_x86. Isn't the x86 Native Tool Command Prompt (i.e. vcvars.bat x86) for native compilation? Meaning that compile on a x86 host to a x86 target? I aim to build on a x64 host to a x86 machine, which means that all my build tools (e.g. qmake) shall be compiled with a native compiler (because I would run them on my 64-bit host), and all the libs I intend to deploy should be compiled to x86.

(So basically this is how I set my build environment for CC, running visual studio 2017's configuration script - vcvars.bat)

jsulm · 27 Nov 2017, 10:21

@v5exp4 There is no need to compile the build tools for x86 as x86_64 can execute x86 binaries.

v5exp4 · J jsulm 27 Nov 2017, 09:41

@jsulm Yes, that is true. However if I set my environment to a x86 toolchain (either amd64_x86 cross or even native x86) it would throw me the same error, meaning that the linker is targeting x64 for my build tools, such as qmake, while my libraries are compiled to x86. Therefore I get the architecture mismatch mentioned in my original post.

It seems that during the configuration of the Qt build it tries and discovers the host platform and sets the target for qmake automatically. Which is fine for me, as I would run qmake on x64 however I need my libraries built for x86 targets.

v5exp4 · S SGaist 24 Nov 2017, 21:08

@SGaist I tried using the native tools, but it would throw me the very same error.

v5exp4 · wrote on 4 Dec 2017, 09:58

@SGaist
I was wrong before. I could properly compile with x86 native tools on x64. The problem was that after previous configurations the cache files were not cleaned properly and setup was stuck for x64 target.

So the problem is worked around, however I still expect that it should be possible to compile with the x64_x86 cross tools. When I run the configure.bat script, the target architecture is listed as x64 (should be i386). Seems that no matter what I do, what flags I try to pass, this is unchanged. Seems that this value is somehow derived from the compiler itself and I am unable to set it to i386 instead of x64.

Does anybody know what flags are necessary to be passed to actually set the target architecture to i386?

Thank you for all your help,
Balazs

SGaist · 5 Dec 2017, 08:16

Is it me or does it look like QTBUG-43457 ?

v5exp4 · S SGaist 4 Dec 2017, 21:31

@SGaist Exactly! Thank you for finding it. I will apply the patch, see how it goes and mark this as solved.

v5exp4 · wrote on 5 Dec 2017, 11:57

I have checked the source code of the qmakeevaluator and the changes are present in version 5.9.1, still it does not recognize the platform. Even if I try to hardcode to the qmake evaluator the following:

vars[ProKey("QMAKE_TARGET.arch")] = ProString("x86");

It does not change a thing, still tries to link qmake to x64.