Why is get_current() not const function?

[Jakub Jelinek <jakub@redhat.com>]

Hi!

E.g. on x86-64,
        NEW_AUX_ENT(AT_UID, (elf_addr_t) current->uid);
        NEW_AUX_ENT(AT_EUID, (elf_addr_t) current->euid);
        NEW_AUX_ENT(AT_GID, (elf_addr_t) current->gid);
        NEW_AUX_ENT(AT_EGID, (elf_addr_t) current->egid);
results in 4 movq %gs:0,%rax instructions while one is completely
enough.
Anyone remembers why get_current function (on arches which define
current to get_current()) is not const and why on x86-64
the movq %%gs:0, %0 inline asm is volatile with "memory" clobber?
AFAIK current ought to be constant in any function with the exception of
schedule.
If the reason is kernel/sched.c, then IMHO it is certainly
worth making get_current const everywhere but in kernel/sched.c
(e.g. through special define in sched.c before any includes).

	Jakub