libcontext currently restores and saves the FPSCR register
on ppc64. This behavior is fine (though unnecessary) on the
ELFv1 ABI which designates the register as volatile, but has
been observed to cause crashes on ELFv2 systems.
The ELFv2 ABI designates the FPSCR register as Limited-access
and specifies specific conditions that must be met to clobber
it. It does not seem that a context swap function meets these
conditions (and indeed, the save/restore register example in the
ABI document does not modify FPSCR).
This patch fixes ELFv2 ABI compliance by removing the FPSCR
save/restore code in libcontext entirely. This fixes observed
crashes on the platform and should have no consequence for
ELFv1 support.
Fixes: lp:1840088
* https://bugs.launchpad.net/kicad/+bug/1840088
Shawn Anastasio
Tomasz Wlostowski
Jean-Samuel Reynaud
Jiaxun Yang
Seth Hillbrand
Maciej Sumiński
Robert Yates
tomasz.