FPSCR is Not Being Saved Across Thread Context Switches

CAUSE

When a process has multiple threads, the FPSCR register is not being saved during the thread context save restore procedure. It is being treated as a per process resource rather than a per thread resource.

For example:

The first thread in a process unmasks a floating point exception, for example divide by zero, and then spawns another thread and waits for it to exit. The other thread unmasks a different exception, for example underflow, and then exits. When the first thread gets scheduled, the FPSCR register is set to underflow being unmasked, but divide by zero being masked. Thus, when the first thread executes, the FPSCR register is set to the state left by the second thread.