Re: Has anyone successfully bootstrapped gcc-4.6.3 on m68k?
On Fri, 18 May 2012, Vincent Rivi?re wrote:
> On 18/05/2012 21:26, Thorsten Glaser wrote:
...
> > That would need to be addressed during porting, sure. We basically
> > need a userspace CPU switch between: - 68020+ or CF, no distinguishing
> > needed (generic mode)
>
> Henk Robbers did that in his AHCC compiler. And it works fine. The
> binaries can run on both 68020+ and ColdFire.
Has anyone benchmarked those binaries (running on the hybrid platform)
against native 68020 and Coldfire binaries (running on their respective
native platforms)?
>
> GCC could probably do the same when configured for the ColdFire 5200
> target. I carefully avoided to do that since I provide 68000, 68020+FPU
> and ColdFire libraries with my cross-tools, so people just have to
> recompile their software to get fully optimized libraries.
>
> Note that while the ColdFire brings very few new instructions in for
> userland, it lacks a lot of 68000 instructions and addressing modes. So
> a compatible binary is almost optimal for ColdFire, but really
> suboptimal for 68020.
It's the slower-clocked 680x0 chips which need that optimisation more than
the faster CF chips need it. So the concept of a generic binary is flawed
IMHO. (But I'd be happy to be proven wrong by suitable benchmarks.)
The hybrid binary idea was discussed on this list some years ago. Notably
in these threads --
http://lists.debian.org/debian-68k/2008/02/msg00217.html
http://lists.debian.org/debian-68k/2007/02/msg00128.html
http://lists.debian.org/debian-68k/2006/08/msg00052.html
http://lists.debian.org/debian-68k/2006/08/msg00040.html
Are there more recent Coldfire devices (newer than V4e) that might help
with the ABI issues?
In anycase, I think that the toolchain maintenance issue that Roman Zippel
raised years ago is probably the most risky aspect of a possible
investment that Debian porters might make in adopting a hybrid ABI/ISA.
Freescale sponsored the Coldfire support in the GNU toolchain; a Debian
port would do well to leverage that rather than contrive a new ABI and
hope to maintain it, given the shortage of skills (and the shortage of CF
hardware owners for that matter).
Finn
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