------- Comment #10 from jeremy at goop dot org 2009-02-09 20:35 ------- The code in question is setting up parameters for a Xen hypercall. The hypercall ABI defines what arguments go in which registers. It uses the "register unsigned long arg asm" syntax because that's the only way to specify high registers on x86-64.
-- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39139
