[CMake] toolchain file - cross-compiling windows-amd64->windows-x86

[Eric Doenges]

We use ninja for building on Windows. Our toolchain file for the MSVC 
compiler is really simple (this is for MSVC 18.0, 32 bits):

--- SNIP ---

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_SYSTEM_PROCESSOR "x86")
set(CMAKE_SYSTEM_VERSION 1)

# Microsoft MSVC compiler
set(CMAKE_C_COMPILER cl.exe)
set(CMAKE_CXX_COMPILER cl.exe)

# Unfortunatly CMake doesn't seem to know anything about the MSVC compiler,
# so tell CMake that cl.exe supports C99
set(CMAKE_C_COMPILE_FEATURES c_std_99)

# If Visual Studio is selected as generator, only allow VS 2013
if(CMAKE_GENERATOR MATCHES "Visual Studio")
   if(NOT CMAKE_GENERATOR MATCHES "Visual Studio 12 2013")
     message(FATAL_ERROR "Visual Studio generator requires Visual Studio 
12 2013"
       " for this configuration")
   else()
     # Enable parallel builds for Visual Studio Projects with the /MP flag
     set(_MP_FLAG "/MP")
   endif()
endif()

set(CMAKE_C_FLAGS_INIT   "/arch:SSE2 ${_MP_FLAG} /EHsc")
set(CMAKE_CXX_FLAGS_INIT "/arch:SSE2 ${_MP_FLAG}")

--- SNIP ---

However, there is a major snag (naturally, since we're talking about 
Windows here) - in order for the Microsoft compiler to work from the 
command line, you need to set the correct environment, and CMake doesn't 
really give you a good way to do this. You can set environment variables 
from CMake, but as the documentation says "This command affects only the 
current CMake process, not the process from which CMake was called, nor 
the system environment at large, nor the environment of subsequent build 
or test processes.".

The solution we use is instead of calling cmake directly, we call a Perl 
script that sets up the environment correctly and then calls cmake for 
configuration or building. An alternative solution would be to write a 
batch script wrapper for cl.exe, something like.

@ECHO OFF
"C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x86
cl.exe %*

and then set this batch script as the C and C++ compiler in CMake (note 
that this is untested - I think it should work, but it may need some 
extra work).

With kind regards,
Eric

Am 17.09.19 um 21:46 schrieb fdk17:
> As I recall for myself, simply using the Visual Studio Generator with 
> the -A option was all that was needed to build for Win32.
> You don't need a toolchain file because the generator already knows 
> how to setup a Visual Studio Project to target Win32.
> Even the documentation for cross-compiling doesn't show a need to 
> setup toolchain file for cross compiling in this case.
>
> I personally never seen anyone try to use the Ninja generator via 
> command line CMake and use the cl.exe compiler.
> I've only seen that using Visual Studio to open a CMakeLists.txt file 
> it can produce a Ninja project.  But even MS documentation states that 
> it doesn't always work.
>
> https://stackoverflow.com/questions/31262342/cmake-g-ninja-on-windows-specify-x64
> This says you should be able to open the proper development window and 
> use Ninja.
>
> The output shows that in the environment you are using it doesn't even 
> know how to use cl.exe to even determine with compiler it is.  Maybe 
> not all the proper environment variables and paths are being set 
> correctly when using the compiler.
>
> --
> F
-- 

*Dr. Eric Dönges*
Senior Software Engineer

MVTec Software GmbH | Arnulfstr. 205 | 80634 Munich | Germany
doenges at mvtec.com <mailto:mustermann at mvtec.com> | Tel: +49 89 457 695-0 
| www.mvtec.com <http://www.mvtec.com>

Find our privacy policy here <https://www.mvtec.com/imprint>.

Sign up <https://www.mvtec.com/newsletter> for our MVTec Newsletter!

Geschäftsführer: Dr. Wolfgang Eckstein, Dr. Olaf Munkelt
Amtsgericht München HRB 114695

MVTec Software GmbH Logo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://cmake.org/pipermail/cmake/attachments/20190918/7cc63d51/attachment.html>