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RE: MIPS PLT entry
- From: "Fu, Chao-Ying" <fu at mips dot com>
- To: "Maciej W. Rozycki" <macro at linux-mips dot org>, "Richard Sandiford" <rdsandiford at googlemail dot com>
- Cc: <binutils at sourceware dot org>
- Date: Tue, 23 Jun 2009 15:15:25 -0700
- Subject: RE: MIPS PLT entry
Maciej W. Rozycki wrote:
> On Sun, 21 Jun 2009, Richard Sandiford wrote:
>
> > > The default sequence is out of question -- with MIPS I
> processors a
> > > failure to observe the load delay slot will make code
> completely unusable
> > > -- there is no interlock. Correctness first, performance second.
> >
> > It's not really "out of the question". As you probably know, there
> > were two competing designs for the PLT stuff, and this was
> very much a
> > question when the two designs were being discussed. One of
> the designs
> > used exactly the kind of cache-friendly 4-insn PLT that
> Chao-Ying wants
> > at the (deliberate) cost of not supporting MIPS I.
>
> I haven't been following discussions in this area -- sorry
> and something
> to regret, I suppose.
>
> > TBH, my position on this was (and still is): forget about
> MIPS I. This
> > is an ABI extension designed in 2007/8. Anyone who wants
> to play with
> > MIPS I as a hooby is free do so, and is free to use modern
> tools to do
> > so. But when it comes to an optional ABI extension like
> this, it seems
> > quite reasonable to leave MIPS I aside and require the use
> of MIPS II
> > or above.
>
> It is reasonable, but there is no point in deliberately
> emitting code
> which is -- by means of ELF file header flags -- known it
> will not work.
> It might make sense to bail out on -mplt with a MIPS I header though,
> however...
>
> > Now we didn't decide to that, which is fine, and I'm not
> asking anyone
> > to reopen that debate. I just don't think this as far
> outside the sphere
> > of opinion as you seem to suggest.
>
> ... it's trivial to implement it flexibly, so that both MIPS
> I support is
> retained and newer platforms benefit from a faster sequence,
> and I plan to
> do so unless Chao-Ying beats me, ;) so I see no point in doing it
> otherwise.
Hi Maciej,
I think your implementation will work. I was busy recently, so please do it.
Thanks a lot!
Regards,
Chao-ying