On Tue, Sep 11, 2012 at 01:29:52AM +0100, Maciej W. Rozycki wrote:

 Relying on any call-clobbered registers, including $7 to be preserved 
across a syscall is risky, to say the least, as this is not guaranteed by 
the syscall ABI.  I do wonder however why we have these instructions to 
save/restore $25 in SAVE_SOME/RESTORE_SOME.  This dates back to 2.4 at the 
very least.

 Ralf, any insights?

It dates back to the initial commit in 36ea5120 from March 27, 1998 for
2.1.90 when for the sake of better lmbench syscall latency numbers I had
introduced the concept of partial saving of a register frame.  I think it
should rather have been in SAVE_TEMP/RESTORE_TEMP instead.

  Ralf