From d8c6becdbe60fbae2264356c048da668b547635e Mon Sep 17 00:00:00 2001
From: guenther <guenther@openbsd.org>
Date: Thu, 27 Jul 2023 00:28:24 +0000
Subject: [PATCH] Follow the lead of mips64 and make cpu_idle_cycle() just call
 the indirect pointer itself and provide an initializer for that going to the
 default "just enable interrupts and halt" path.

ok kettenis@
---
 sys/arch/amd64/amd64/locore.S  | 14 +++++---------
 sys/arch/amd64/amd64/machdep.c |  5 +++--
 sys/arch/amd64/include/cpu.h   |  3 ++-
 3 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/sys/arch/amd64/amd64/locore.S b/sys/arch/amd64/amd64/locore.S
index c2536e7395b..2046f0997c8 100644
--- a/sys/arch/amd64/amd64/locore.S
+++ b/sys/arch/amd64/amd64/locore.S
@@ -1,4 +1,4 @@
-/*	$OpenBSD: locore.S,v 1.137 2023/07/25 06:48:37 guenther Exp $	*/
+/*	$OpenBSD: locore.S,v 1.138 2023/07/27 00:28:24 guenther Exp $	*/
 /*	$NetBSD: locore.S,v 1.13 2004/03/25 18:33:17 drochner Exp $	*/
 
 /*
@@ -473,21 +473,17 @@ bogus_proc_pmap:
 #endif /* DIAGNOSTIC */
 END(cpu_switchto)
 
-/* placed here for correct static branch prediction in cpu_idle_* */
 NENTRY(retpoline_rax)
 	JMP_RETPOLINE(rax)
 
-ENTRY(cpu_idle_cycle)
-	RETGUARD_SETUP(cpu_idle_cycle, r11)
-	movq	cpu_idle_cycle_fcn,%rax
-	cmpq	$0,%rax
-	jne	retpoline_rax
+ENTRY(cpu_idle_cycle_hlt)
+	RETGUARD_SETUP(cpu_idle_cycle_hlt, r11)
 	sti
 	hlt
-	RETGUARD_CHECK(cpu_idle_cycle, r11)
+	RETGUARD_CHECK(cpu_idle_cycle_hlt, r11)
 	ret
 	lfence
-END(cpu_idle_cycle)
+END(cpu_idle_cycle_hlt)
 
 /*
  * savectx(struct pcb *pcb);
diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index ddbeedb12b5..453de13fbfb 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.285 2023/07/10 03:32:10 guenther Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.286 2023/07/27 00:28:25 guenther Exp $	*/
 /*	$NetBSD: machdep.c,v 1.3 2003/05/07 22:58:18 fvdl Exp $	*/
 
 /*-
@@ -160,7 +160,8 @@ char machine[] = MACHINE;
 /*
  * switchto vectors
  */
-void (*cpu_idle_cycle_fcn)(void) = NULL;
+void cpu_idle_cycle_hlt(void);
+void (*cpu_idle_cycle_fcn)(void) = &cpu_idle_cycle_hlt;
 
 /* the following is used externally for concurrent handlers */
 int setperf_prio = 0;
diff --git a/sys/arch/amd64/include/cpu.h b/sys/arch/amd64/include/cpu.h
index b5784abe689..cf322886269 100644
--- a/sys/arch/amd64/include/cpu.h
+++ b/sys/arch/amd64/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.157 2023/07/25 18:16:19 cheloha Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.158 2023/07/27 00:28:24 guenther Exp $	*/
 /*	$NetBSD: cpu.h,v 1.1 2003/04/26 18:39:39 fvdl Exp $	*/
 
 /*-
@@ -406,6 +406,7 @@ void	cpu_proc_fork(struct proc *, struct proc *);
 int	amd64_pa_used(paddr_t);
 #define	cpu_idle_enter()	do { /* nothing */ } while (0)
 extern void (*cpu_idle_cycle_fcn)(void);
+#define	cpu_idle_cycle()	(*cpu_idle_cycle_fcn)()
 #define	cpu_idle_leave()	do { /* nothing */ } while (0)
 
 struct region_descriptor;
-- 
2.20.1