[Libre-soc-bugs] [Bug 981] Support PowerPC ABI in cavatools

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=981

--- Comment #8 from Dmitry Selyutin <ghostmansd at gmail.com> ---
(In reply to Jacob Lifshay from comment #7)
> (In reply to Dmitry Selyutin from comment #6)
> > Deal?
> 
> ok with me
> 
> > I'd say it fits bug #982.
> 
> i was thinking #982 would only end up with a few syscalls implemented since
> luke was advocating for just open/openat, close, exit, read, and write (or
> something), so the additional budget here would allow implementing a lot
> more.

mmap. This is a blocker. It needs to be done. Plus free pages list, basically a
trivial allocator.

> > I don't expect much to be done there; also parts
> > of it fit ELF support which I, frankly speaking, find to be underrated.
> 
> what do you mean by underrated? that the 1900 EUR estimate is too big? that
> it's too small? something else?

Too small, rationale below.

> keep in mind there is 6000 eur available in the ELF task's budget parent and
> since the statically-linked ELF task is too small I want to add
> dynamically-linked executable support as a separate task and implement more
> syscalls ... if there's not enough work to take up the 2mo of funds then
> I'll add more.

I expect several problems there. First of all, you'll have to implement mmap
support, and this includes introducing something like a free list for
bookkeeping the memory allocations, even if these are backed just by the big
mapping. Second, you'll have to support different sections differently, not
just "parse and map at fixed offset". Third, I expect some challenges in
ISACaller and a learning curve with pyelf (if we take it; if not, this is even
worse). I'd say with all the stuff I mentioned it's already no less than 4-5K.
But, as I said, it's up to task owner to rate it budget-wise, I'm just
expressing my considerations.

And, since you mentioned dynamic linkage. I expect it to be damn hard and
time-nsuming based on my experience with relocations. Most of the task will be
reading ELF and architecture specs. The code size won't be that huge; but the
amount of time will... Again, your estimations might be different.

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