On Fri, Aug 10, 2018 at 09:10:04PM -0700, Richard Henderson wrote:
On 08/10/2018 07:45 PM, Al Viro wrote:
BTW, seeing that it's your code - why was unop used in alpha_ni_syscall? I don't remember the rules re pipeline stalls; is it that some earlier variants prefer unop to nop in such places? It's not that microoptimizing that one makes any difference, but just out of curiosity - would something like lda $0, -ENOSYS stq $sp, 0($sp) /* sp != 0 */ ret do just as well there?
Oh that. Well, unop is a "load" and pairs with everything on all cpus, where nop is an integer and doesn't always pair. So I got into the habit of using unop for everything.
The extra nop was so that lda + unop // stq + ret paired up in in two cycles as opposed to lda /stall/ stq // ret in three cycles on ev4+ev5. ev6 didn't care. FWIW.
BTW, looking through old patches around entry.S, are you OK with this one? Same kind of macro as that for fork/vfork/clone glue...
diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S index c64806a2daf5..828d641b4410 100644 --- a/arch/alpha/kernel/entry.S +++ b/arch/alpha/kernel/entry.S @@ -791,7 +791,7 @@ ret_from_kernel_thread: /* * Special system calls. Most of these are special in that they either - * have to play switch_stack games or in some way use the pt_regs struct. + * have to play switch_stack games. */
.macro fork_like name @@ -812,35 +812,25 @@ fork_like fork fork_like vfork fork_like clone
+.macro sigreturn_like name .align 4 - .globl sys_sigreturn - .ent sys_sigreturn -sys_sigreturn: + .globl sys_\name + .ent sys_\name +sys_\name: .prologue 0 lda $9, ret_from_straced cmpult $26, $9, $9 lda $sp, -SWITCH_STACK_SIZE($sp) - jsr $26, do_sigreturn + jsr $26, do_\name bne $9, 1f jsr $26, syscall_trace_leave 1: br $1, undo_switch_stack br ret_from_sys_call -.end sys_sigreturn +.end sys_\name +.endm
- .align 4 - .globl sys_rt_sigreturn - .ent sys_rt_sigreturn -sys_rt_sigreturn: - .prologue 0 - lda $9, ret_from_straced - cmpult $26, $9, $9 - lda $sp, -SWITCH_STACK_SIZE($sp) - jsr $26, do_rt_sigreturn - bne $9, 1f - jsr $26, syscall_trace_leave -1: br $1, undo_switch_stack - br ret_from_sys_call -.end sys_rt_sigreturn +sigreturn_like sigreturn +sigreturn_like rt_sigreturn
.align 4 .globl alpha_ni_syscall