Re: CVS commit: src/lib/libm

[Martin Husemann <martin%duskware.de@localhost>]

On Tue, Oct 29, 2024 at 07:59:45PM +0000, Taylor R Campbell wrote:
> Yes, I think we need a new MACHINE_ARCH for that, maybe m68ksf.  But
> maybe effort is better spent on making FPU_EMULATE work than on
> dealing with a new ABI.

I think this is impossible w/o compiler/linker support and doing special
userland builds for the affected CPUs.

And when you need a special userland, the softloat thing is the easier
way out :-)

Basically Apple shipped "a few" systems with a pre-production LC040 chip
that has a mask error that kills emulation of the fpu instructions as
the chip looses data when it handles the "unimplemented" trap for 0xF.......
instructions.

The errata is hard to find nowadays, PR 13078 has the info.

Possible workarounds:

 - use softfloat userland
 - replace chip with a fixed LC040 or a full MC040
 - use userland compiled so that it has a NOP before any FPU instruction

Martin