[PATCH 6/13] mips musl support

[Matthew Fortune]

Jeff Law <law@redhat.com> writes:
> On 05/08/2015 10:50 AM, Joseph Myers wrote:
> >
> > Note that however the dynamic linker does properly need to save and
> > restore call-clobbered registers used for argument passing (because of
> > IFUNCs, user-provided malloc, audit hooks etc. that might affect them
> > even if the dynamic linker itself doesn't); see
> > <https://sourceware.org/ml/libc-alpha/2014-01/msg00673.html>.  So any
> > floating-point-agnostic dynamic linker would, if fixing the bugs
> > around not saving / restoring such registers, need to have
> > runtime-conditional code to save and restore them rather than simple
> > compile-time conditionals.
> Right.  So there has to be some reasonable cost way to find out if you
> have FPU registers at runtime, then select between the code paths at
> runtime.

Indeed and I think there are many ways to achieve that without hardware
support as the cost of loading a global variable in the dynamic linker
wouldn't be significant. I think MIPS ABIs are the only ones with enough
information available at runtime to achieve this currently but the
principles should apply to any arch.

The work we are investigating as part of PR65862 will help all this
as the intention is to avoid FPR usage unless floating point is actually
used. There is then some thinking involved in figuring out what no-float
should really mean: i.e. no floating point types used, no FPU insns used
and/or no floating point in any of the calls/global functions. I haven't
spent enough time thinking about which ones are the most important from
above yet.

Matthew