120a25d68a
If we don't do this here there's a 1 instruction race where an interrupt could come in and crash the user process due to having no stack. 2. Pass %fsr to the user trap handler in %l4. Since %fsr can only be loaded from or stored to memory, we need to do some contortions and temporarily save it to the alternate global stack. 3. Reload the pcb and pcpu registers for traps in kernel mode, for sanity. Submitted by: tmm (1, 2)
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