cross-compiling with GHC

[Peter Tanski]

Ian Lynagh wrote,

> On Fri, Dec 15, 2006 at 03:08:24PM -0800, Mathew Mills wrote:
>> I want to be able to build a version of GHC that runs on x86 but
>> generates binaries that will run natively on x86_64.
>
> I don't think there would be any major technical difficulties in  
> adding
> support, just a lot of assumptions in the compiler, libraries and  
> build
> system that we are generating code for the architecture that we are  
> on,
> so it could eat quite a bit of time.

Cross compiling using -fvia-C would seem to be easier (assuming your  
GCC is a cross-compiler) and of course you would have to build an  
x86_64 version of the RTS and other libraries that may be linked in  
(currently, statically except on OS X, but that may change soon since  
Wolfgang Thaller got PIC going in the Native Code Generator (NCG),  
see Commentary/PositionIndependentCode).  As for other settings, the  
Mangler (driver/mangler/ghc-asm.lprl), for example, runs according to  
$TargetPlatform, set by the build system into one small Perl script  
("ghc-asm")--you would need to change the build system and the  
compiler commands to use different targets.

One of the worst problems is the NCG: it currently targets only one  
architecture (machine, OS) as it is pieced together by conditional  
defines from the build system.  The right way to go about doing cross- 
compilation with the NCG involves moving the architecture specific  
parts into separate modules and binding them into the compiler with  
dynamic options.  To my knowledge, this is a far-off goal.  The  
benefit (from what I am doing) would be the ability to use a simple  
cross-compiling assembler to assemble the code generated by the NCG  
for a number of different architectures (x86, x86_64, including AMD)  
and different file formats (COFF, Win32-COFF, OBJ, ELF).  I am  
currently modifying GHC to use the Yasm modular assembler <http:// 
www.tortall.net/projects/yasm/> for Windows-native code but it would  
also be usable for other x86 architectures.

I have been rooting around in the system for a little while now-- 
including command options, NCG modifications and the build system, so  
if you have any questions feel free to ask.

Cheers,
Pete Tanski