On Sep 20, 2016 5:25 PM, "Josh Poimboeuf" <jpoim...@redhat.com> wrote: > > On Tue, Sep 20, 2016 at 09:10:55PM -0400, Brian Gerst wrote: > > Dropping asmlinkage from schedule_tail() would be a better option if > > possible. > > My understanding is that it's still needed for ia64. AFAICT, ia64 > relies on schedule_tail() having the syscall_linkage function attribute. > From the gcc manual: > > This attribute is used to modify the IA64 calling convention by > marking all input registers as live at all function exits. This makes > it possible to restart a system call after an interrupt without having > to save/restore the input registers. This also prevents kernel data > from leaking into application code.
/me needs to excise this from i386. The amount of BS code involved to avoid a whopping *six* register saves per syscall was absurd. > > And the ia64 entry code has some similar language: > > /* > * Invoke schedule_tail(task) while preserving in0-in7, which > may be needed > * in case a system call gets restarted. > */ > GLOBAL_ENTRY(ia64_invoke_schedule_tail) > ... That comment has to be wrong. What syscall could possibly be restarted across schedule_tail()? It's a brand new thread and has literally never done a syscall. There may be another reason that the registers are live there, but I generally do my best to never look at ia64 asm code.
