On 19 July 2014 02:57, <[email protected]> wrote: > would it make sense to save and restore the two registers > on syscall entry/exit, so userspace programs could make use > of them for per process data? >
Good question. None of the others need to be saved and restored because they are defined to be dead on entry to a function, but you're right that rule doesn't really apply to extern register, and they could be useful. _tos only works when every process has at least one stack always at the same fixed virtual address. On the other hand, a kernel that provides an alternative to that would also know to save and restore extern registers.
