This commit re-implements the SPARC V8 ABI "Flush windows" software
trap. The trap is generated by C++ compilers for exceptions and also by
the C standard library function longjmp().
There were two issues with the previous implementation:
1. It did reads and writes via the stack pointer of the trap window,
which is not defined.
2. It executed with traps enabled but without the processor run-time
state set to safely handle traps. In particular there was no valid
stack for trap processing. Even though interrupt priority was set to
highest level, the behavior at other traps was not deterministic. For
example non-maskable interrupt (15) trap or bus error trap for
instruction fetch.
This new implementation does not store backup copies of CPU registers to
the stack, and it executes with traps disabled.
Fixes#63901
Signed-off-by: Martin Åberg <martin.aberg@gaisler.com>
fd4e66499c