[qcc] TCG

[Rob Landley]

On 05/08/2015 04:33 PM, Bruce Ewing wrote:
> I've been digging through the actual TCG code, and I've discovered the
> following:
> 
> The list of supported QEMU CPUs above are QEMU *frontends*, and are
> mostly not available as TCG backends.
> 
> TCG supports precisely eight backends: x86, ia64, mips, sparc, arm,
> powerpc, s390, and aarch64. The aarch64 backend, however, is GPLv2
> licensed -- so that one is out.

Ouch.

Early on (when tcg was first introduced) the code was symmetrical, if
you had a frontend it had to also work s a backend.  Apparently they
optimized that out in the past few years. :(

Sadness.

What I was really hoping was if we could get qemu developers interested
in using this, they might fill in missing needed bits. (I don't want to
_fork_ tcg. If anything it would be nice to contribute a working cc
frontend upstream into the qemu repository, although this seems unlikely
to fly. Secondly would be to make tcg a subrepo the way qemu has a
couple existing subrepos it won't build without already...)

> The TCG code itself is simply the backend from TCC, almost completely
> unmodified (some sections deleted, and a few tiny features added to
> support QEMU). Which means that all of the code that is missing to turn
> it into a C compiler backend are already available in TCC.
> 
> Which means that it should be completely brainless to attach it to QCC
> as a backend -- where any other backend would require some thought. So
> it looks like TCG does indeed win as the easiest backend.

Yay!

That's sort of what it looked like, but I never had time to do a proper
deep dive into the code.

Thanks,

Rob

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