Crosscompilation on Mac

1. install xcode: http://itunes.apple.com/us/app/xcode/id497799835
   1. install xcode command line tools: xcode-select --install
   2. agree to Xcode license in Terminal: sudo xcodebuild -license
2. install macports
   1. https://www.macports.org/install.php
3. sudo port install glib2 intltool p5-xml-parser gpatch scons wget xz
4. clone repo
   1. git clone -b master https://github.com/mxe/mxe.git
5. make build-requirements from within mxe dir
6. change settings.mk for desired targets
7. build gcc first time
   1. make gcc winpthreads
   2. http://stackoverflow.com/questions/24417906/mingw-vs-mingw-w64-vs-msvc-vc-in-cross-compiling
8. change gcc.mk
   1. --enable-threads=posix
   2. add winpthreads to "$(PKG)_DEPS :="

Notes

• http://qt-project.org/wiki/MinGW-64-bit
• http://sourceforge.net/p/mingw-w64/bugs/344/
• http://wiki.dwarfstd.org/index.php?title=Exception_Handling
  • Relationship with DWARF
    Although the C++ ABI data in the .eh_frame section uses the data format described by the DWARF Standard (with some extensions), this section (and other sections used by exception handling, such as .eh_frame_hdr and .gcc_except_table) are not defined by the DWARF Standard. The DWARF Standard does not describe the extensions to support exception handling nor the routines which must be called by a program to use this data. The DWARF Debugging Format Committee does not specify the contents of these sections or the functionality which must be provided by the language run time system to support exception handling.
    The .eh_frame section is not used for debugging. Whether it is generated or not is independent of whether DWARF debug data is generated. All DWARF data is contained in sections with names starting with .debug, which may be removed from a program without affecting the program's normal execution. It is common practice to "strip" debugging sections from a program before putting it into production, either to reduce the program size, make reverse engineering more difficult, or both.
    Removing the .eh_frame section (whether the DWARF .debug sections are left in place or not) has a high likelihood of adversely affecting a program's behaviour, especially when it encounters an unexpected condition.
    Unfortunately, it has been a common shorthand to refer to the C++ ABI exception handling methodology using .eh_frame with "DWARF exception handling," or similar phrases. Perhaps this because it is easier to say this than the unwieldy "C++ exception handling using the DWARF Call Frame Information format with extensions", or the misleading "C++ ABI for IA-64" or "SVR4 ABI AMD64 Processor Supplement", especially when discussing a processor other than Itanium or AMD-64. This leads to occasional confusion, where people may look at the DWARF Specification for a description of the C++ ABI exception handling method, or where vulnerabilities in the EH scheme are incorrectly characterized as DWARF vulnerabilities, as in the otherwise excellent paper mentioned below.

Stuff

Why doesn't mingw-w64 gcc support Dwarf-2 Exception Handling?

The Dwarf-2 EH implementation for Windows is not designed at all to work under 64-bit Windows applications. In win32 mode, the exception unwind handler cannot propagate through non-dw2 aware code, this means that any exception going through any non-dw2 aware "foreign frames" code will fail, including Windows system DLLs and DLLs built with Visual Studio. Dwarf-2 unwinding code in gcc inspects the x86 unwinding assembly and is unable to proceed without other dwarf-2 unwind information.

The SetJump LongJump method of exception handling works for most cases on both win32 and win64, except for general protection faults. Structured exception handling support in gcc is being developed to overcome the weaknesses of dw2 and sjlj. On win64, the unwind-information are placed in xdata-section and there is the .pdata (function descriptor table) instead of the stack. For win32, the chain of handlers are on stack and need to be saved/restored by real executed code.

qt-project.org/wiki/MinGW-64-bit

SJLJ (setjmp/longjmp): – available for 32 bit and 64 bit – not “zero-cost”: even if an exception isn’t thrown, it incurs a minor performance penalty (~15% in exception heavy code) – allows exceptions to traverse through e.g. windows callbacks

DWARF (DW2, dwarf-2) – available for 32 bit only – no permanent runtime overhead – needs whole call stack to be dwarf-enabled, which means exceptions cannot be thrown over e.g. Windows system DLLs.

SEH (zero overhead exception) – will be available for 64-bit GCC 4.8.