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Re: RTABI half-precision conversion functions (ping)
- From: Julian Brown <julian at codesourcery dot com>
- Cc: <gcc-patches at gcc dot gnu dot org>, <ams at codesourcery dot com>, Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>, <rearnsha at arm dot com>
- Date: Tue, 24 Jun 2014 12:24:13 +0100
- Subject: Re: RTABI half-precision conversion functions (ping)
- Authentication-results: sourceware.org; auth=none
- References: <20120719132816 dot 2b51c0bc at octopus> <201207191354 dot 58297 dot paul at codesourcery dot com> <20120719144754 dot 514db0e3 at octopus> <20140529111652 dot 66742970 at octopus>
On Thu, 29 May 2014 11:16:52 +0100
Julian Brown <julian@codesourcery.com> wrote:
> On Thu, 19 Jul 2012 14:47:54 +0100
> Julian Brown <julian@codesourcery.com> wrote:
>
> > On Thu, 19 Jul 2012 13:54:57 +0100
> > Paul Brook <paul@codesourcery.com> wrote:
> >
> > > > But, that means EABI-conformant callers are also perfectly
> > > > entitled to sign-extend half-float values before calling our
> > > > helper functions (although GCC itself won't do that). Using
> > > > "unsigned int" and taking care to only examine the low-order
> > > > bits of the value in the helper function itself serves to fix
> > > > the latent bug, is compatible with existing code, allows us to
> > > > be conformant with the eabi, and allows use of aliases to make
> > > > the __gnu and __aeabi functions the same.
> > >
> > > As long as LTO never sees this mismatch we should be fine :-)
> > > AFAIK we don't curently have any way of expressing the actual ABI.
> >
> > Let's not worry about that for now :-).
> >
> > > > The patch no longer applied as-is, so I've updated it (attached,
> > > > re-tested). Note that there are no longer any target-independent
> > > > changes (though I'm not certain that the symbol versions are
> > > > still correct).
> > > >
> > > > OK to apply?
> > >
> > > I think this deserves a comment in the source. Otherwise it's
> > > liable to get "fixed" in the future :-) Something allong the lines
> > > of "While the EABI describes the arguments to the half-float
> > > helper routines as 'short', it does not require that they be
> > > extended to full register width. The normal ABI requres that the
> > > caller sign/zero extend short values to 32 bit. We use unsigned
> > > int arguments to prevent the gcc making assumptions about the
> > > high half of the register."
> >
> > Here's a version with an explanatory comment. I also fixed a couple
> > of minor formatting nits I noticed (they don't upset the diff too
> > much, I don't think).
>
> It looks like this one got forgotten about. Ping?
>
> Context:
>
> https://gcc.gnu.org/ml/gcc-patches/2012-07/msg00902.html
> https://gcc.gnu.org/ml/gcc-patches/2012-07/msg00912.html
>
> This is an EABI-conformance fix.
Ping?
Julian