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[RFC] cygport: cross-compiling to embedded systems

Previous discussions (and my examples) on cross-compiling were focused
on other operating systems: MinGW, Linux, and Solaris.  But there is
another use of cross-compiling: "bare metal" embedded systems.
Yesterday I built my first example of such: the AVR toolchain, a sample
build of which is now alongside the others:

Two issues arose when dealing with AVR:

1) cygport had been fully canonicalizing triplets, so "avr" became the
oh-so-informative "avr-unknown-none".  Fedora and Debian both use just
"avr", as that naming is expected by the toolchain.  These seem to be
common with embedded systems, so I changed cygport to remove "-unknown"
and "-none" from triplets.

2) While sysroots make sense for full-OS cross-compiles, where one needs
a location to hold a number of cross-compiled libraries arranged as if
on a native system, it seems not to be the case for embedded systems.
AFAICS with AVR, programs are more unique to the board and most
general-purpose software isn't meant to compile against avr-libc (or is
it the other way around?).  

So having /usr/avr/sys-root/usr/{include,lib} seemed wrong for two
reasons: a) there is no comparable "native" /usr/{include,lib} on a
bare-metal system, and b) using a sysroot just for avr-libc seemed a bit
overkill.  The alternative is to not build binutils/gcc with sysroots,
configure avr-libc (and same goes for newlib on $cpu-elf embeddeds) with
--prefix=/usr and let them install into /usr/$arch/{include,lib} as they
are designed.  This is also how they are packaged on Fedora and Debian
(even though Fedora does use sysroots for mingw*).

Now I have ZERO experience with embedded systems, so I could be way off
on my assessments here.  Can anybody that *does* have some experience
with these provide some further insight?  Furthermore, for which systems
should this apply?


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