A quick Google search suggests that SPARC lacks push/pop instructions. My guess is that the person who wrote this was well versed in SPARC assembly and did in x

A quick Google search suggests that SPARC lacks push/pop instructions. My guess is that the person who wrote this was well versed in SPARC assembly and did in x86 what he would do in SPARC. push/pop would make this code better, but I would not expect a measurable improvement in system performance from using it here. The improvement should be too small relative to all of the other things that happen in system call code paths. The time spent improving this would probably be better spent improving another area.