Cross compiling Windows extensions on a Linux host

1) Build the mingw64 toolchain from scratch with the MingGW-w64 Build Script 3.5.0 to be found on http://zeranoe.com/scripts/mingw_w64_build/mingw-w64-build-3.5.0 which is actually (Nov 2013) based on MinGW-w64 3.0.0 and GCC 4.8.1.

./mingw-w64-build-3.5.0 --build-type=multi --default-configure --disable-shared --enable-gendef

In the directories mingw-w64-i686 and mingw-w64-x86_64 you will find all the necessary toolchain binaries.

2) Take the mingw64 gcc into your PATH variable, e.g. for 32bit version:

export PATH="~/mingw64/mingw-w64-i686/bin:$PATH"

and build a Windows version of Tcl to get an appropriate libstubtcl85.a. Note: You have to replace the macro EXCEPTION_REGISTRATION by TCL_EXCEPTION_REGISTRATION in the files tclWin32Dll.c, tclWinChan.c and tclWinFCmd.c

Alexey Pavlov is offering a patch on his github site: https://github.com/Alexpux/mingw-builds/blob/master/patches/tcl/tcl-8.6.1-mingwexcept.patch

If you rebuild the Tcl system don’t forget to type before configuration:

make clean
make distclean

3) Then go on to build your extension with defining the prefixes, the source, the include and the lib path, e.g.:

# 32bit
GCCPATH=~/mingw64/mingw-w64-i686/bin/
PREFIX=$GCCPATH/i686-w64-mingw32

# 64bit
# GCCPATH=~/mingw-w64-x86_64/bin
# PREFIX=$GCCPATH/x86_64-w64-mingw32

export CC=$PREFIX-gcc
export CXX=$PREFIX-g++
export CPP=$PREFIX-cpp
export RANLIB=$PREFIX-ranlib
export LD=$PREFIX-ld
...

Then we finally start the build process:

$CC -Wall -shared -DUSE_TCL_STUBS \
-I $TCL_INCLUDE -o my_extension.dll $SRCPATH/my_extension.c \
-L $TCL_WIN_BUILD -ltclstub85

Note: To successfully build the stretchkey extension we have to add the definition -DRUNTIME_ENDIAN otherwise Tcllib’s SHA256 module will offer wrong results. In the following 32bit example libtclstub85.a has been copied into the mingw64 32bit library:

$CC -Wall -shared -DRUNTIME_ENDIAN -DUSE_TCL_STUBS \
-I $TCL_INCLUDE -o stretchkey.dll $SRCPATH/stretch.c $SRCPATH/sha256.c \
-L ~/mingw64/mingw-w64-x86_64/lib32 -ltclstub85