[RFC] external compiler support

[Warner Losh]

On Feb 27, 2013, at 10:50 AM, Simon J. Gerraty wrote:

> 
> On Wed, 27 Feb 2013 09:08:05 -0700, Warner Losh writes:
>>> I think this will work, but it is kludgy.  I had created a __X=<prefix-path>
>> 
>> I also am having trouble finding my full patch, but a partial patch can be fou
> 
> I prefer this approach too, but would use a more explicit variable than
> __X (which I could easily imagine someone thinking they could safely use
> within their own makefile for some purpose).
> Eg. we currently have stuff like:
> 
> CC?=      ${BUILD_TOOL_PREFIX}/${CROSS_TARGET_PREFIX}gcc
> 
> since these aren't variables that anyone needs to manipulate regularly
> a little verbosity doesn't hurt.

That stray / will kill you :)

The __X thing (which I'll grant could be better named, but it is in a file that needs to be very pure and I don't know if POSIX allows __ prefix for purely internal things on make or not) was intended to encompass everything you'd need, whether that is just /usr/local/arm-freebsd/bin or something more complicated like /usr/local/bin/arm-linux-gnueabi- whatever.

> Further, having them composed from other bits can also be useful
> (eg. most dev machines here use nfs mounted toolchains, but others use
> local toolchains).
> 
> So (probably taking things too far - I didn't come up with all this ;-)
> 
> BUILD_TOOL_PREFIX?= ${TOOLCHAIN_PREFIX}/${TOOLCHAIN_${MACHINE}}/bin
> CROSS_TARGET_PREFIX?= ${CROSS_TARGET}-
> CROSS_TARGET?= ${CROSS_TARGET_${MACHINE}}
> 
> and a toolchain.mk sets CROSS_TARGET_* for all the supported machines.

Yea, that likely does take things a bit far.

> Of course as you note:
> 
>> I've also started looking into using clang --mumble to doing cross builds too,
> 
> can simplify things (for some value of "--mumble); I managed to get
> clang to produce i386 apps on amd64, but the "--mumble" wasn't obvious
> or documented (that I could find) and infact the man page implied other 
> things that don't work.

Yea, they only half work right now. '-ccc-host-triple arm-none-freebsd -msoft-float -march armv5' might be a typical --mumble that one would want to do. It generates the right .s file, but uses the wrong assembler.

Warner