Clean up more ancient history: since 2015 the libc stubs for

fork/vfork/__tfork haven't cared about the second return register.
So, stop setting retval[1] in kern_fork.c and stop setting the
second return register in the MD child_return() routines.

With the above, we have no multi-register return values on LP64,
so stop touching that register in the trapframe on those archs.

testing miod@ and aoyama@
ok miod@

11 files changed, 20 insertions, 41 deletions

diff --git a/sys/arch/alpha/alpha/trap.c b/sys/arch/alpha/alpha/trap.c
index 3541c81d488..a0379b92e52 100644
--- a/sys/arch/alpha/alpha/trap.c
+++ b/sys/arch/alpha/alpha/trap.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: trap.c,v 1.103 2022/08/29 06:08:03 jsg Exp $ */
+/* $OpenBSD: trap.c,v 1.104 2022/11/02 07:20:07 guenther Exp $ */
 /* $NetBSD: trap.c,v 1.52 2000/05/24 16:48:33 thorpej Exp $ */
 
 /*-
@@ -569,7 +569,6 @@ syscall(code, framep)
 	switch (error) {
 	case 0:
 		framep->tf_regs[FRAME_V0] = rval[0];
-		framep->tf_regs[FRAME_A4] = rval[1];
 		framep->tf_regs[FRAME_A3] = 0;
 		break;
 	case ERESTART:
@@ -604,7 +603,6 @@ child_return(arg)
 	 * Return values in the frame set by cpu_fork().
 	 */
 	framep->tf_regs[FRAME_V0] = 0;
-	framep->tf_regs[FRAME_A4] = 0;
 	framep->tf_regs[FRAME_A3] = 0;
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/amd64/amd64/trap.c b/sys/arch/amd64/amd64/trap.c
index 334502b2e3f..53707fbc99c 100644
--- a/sys/arch/amd64/amd64/trap.c
+++ b/sys/arch/amd64/amd64/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.90 2021/12/09 00:26:11 guenther Exp $	*/
+/*	$OpenBSD: trap.c,v 1.91 2022/11/02 07:20:07 guenther Exp $	*/
 /*	$NetBSD: trap.c,v 1.2 2003/05/04 23:51:56 fvdl Exp $	*/
 
 /*-
@@ -580,14 +580,13 @@ syscall(struct trapframe *frame)
 	}
 
 	rval[0] = 0;
-	rval[1] = frame->tf_rdx;
+	rval[1] = 0;
 
 	error = mi_syscall(p, code, callp, argp, rval);
 
 	switch (error) {
 	case 0:
 		frame->tf_rax = rval[0];
-		frame->tf_rdx = rval[1];
 		frame->tf_rflags &= ~PSL_C;	/* carry bit */
 		break;
 	case ERESTART:
@@ -614,7 +613,6 @@ child_return(void *arg)
 	struct trapframe *tf = p->p_md.md_regs;
 
 	tf->tf_rax = 0;
-	tf->tf_rdx = 1;
 	tf->tf_rflags &= ~PSL_C;
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/arm64/arm64/syscall.c b/sys/arch/arm64/arm64/syscall.c
index e30e6fd0671..84653fe0f58 100644
--- a/sys/arch/arm64/arm64/syscall.c
+++ b/sys/arch/arm64/arm64/syscall.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: syscall.c,v 1.10 2022/01/01 18:52:36 kettenis Exp $ */
+/* $OpenBSD: syscall.c,v 1.11 2022/11/02 07:20:08 guenther Exp $ */
 /*
  * Copyright (c) 2015 Dale Rahn <drahn@dalerahn.com>
  *
@@ -82,15 +82,13 @@ svc_handler(trapframe_t *frame)
 	}
 
 	rval[0] = 0;
-	rval[1] = frame->tf_x[1];
+	rval[1] = 0;
 
 	error = mi_syscall(p, code, callp, args, rval);
 
 	switch (error) {
 	case 0:
 		frame->tf_x[0] = rval[0];
-		frame->tf_x[1] = rval[1];
-
 		frame->tf_spsr &= ~PSR_C;	/* carry bit */
 		break;
 
@@ -122,7 +120,6 @@ child_return(void *arg)
 	struct trapframe *frame = p->p_addr->u_pcb.pcb_tf;
 
 	frame->tf_x[0] = 0;
-	frame->tf_x[1] = 1;
 	frame->tf_spsr &= ~PSR_C;	/* carry bit */
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/hppa/hppa/trap.c b/sys/arch/hppa/hppa/trap.c
index d5080df7e3e..da735f48308 100644
--- a/sys/arch/hppa/hppa/trap.c
+++ b/sys/arch/hppa/hppa/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.158 2022/08/12 17:19:52 miod Exp $	*/
+/*	$OpenBSD: trap.c,v 1.159 2022/11/02 07:20:07 guenther Exp $	*/
 
 /*
  * Copyright (c) 1998-2004 Michael Shalayeff
@@ -641,7 +641,6 @@ child_return(void *arg)
 	 * Set up return value registers as libc:fork() expects
 	 */
 	tf->tf_ret0 = 0;
-	tf->tf_ret1 = 1;	/* ischild */
 	tf->tf_t1 = 0;		/* errno */
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/m88k/m88k/trap.c b/sys/arch/m88k/m88k/trap.c
index b1956c8ef49..d2937dbc415 100644
--- a/sys/arch/m88k/m88k/trap.c
+++ b/sys/arch/m88k/m88k/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.122 2022/08/12 08:31:06 jsg Exp $	*/
+/*	$OpenBSD: trap.c,v 1.123 2022/11/02 07:20:07 guenther Exp $	*/
 /*
  * Copyright (c) 2004, Miodrag Vallat.
  * Copyright (c) 1998 Steve Murphree, Jr.
@@ -1397,7 +1397,6 @@ child_return(arg)
 
 	tf = (struct trapframe *)USER_REGS(p);
 	tf->tf_r[2] = 0;
-	tf->tf_r[3] = 0;
 	tf->tf_epsr &= ~PSR_C;
 	/* skip br instruction as in syscall() */
 #ifdef M88100
diff --git a/sys/arch/mips64/mips64/trap.c b/sys/arch/mips64/mips64/trap.c
index f4a06919cae..d044afd73e5 100644
--- a/sys/arch/mips64/mips64/trap.c
+++ b/sys/arch/mips64/mips64/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.160 2022/10/07 14:59:39 deraadt Exp $	*/
+/*	$OpenBSD: trap.c,v 1.161 2022/11/02 07:20:08 guenther Exp $	*/
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -477,7 +477,7 @@ fault_common_no_miss:
 		}
 
 		rval[0] = 0;
-		rval[1] = locr0->v1;
+		rval[1] = 0;
 
 #if defined(DDB) || defined(DEBUG)
 		trapdebug[TRAPSIZE * ci->ci_cpuid + (trppos[ci->ci_cpuid] == 0 ?
@@ -489,7 +489,6 @@ fault_common_no_miss:
 		switch (error) {
 		case 0:
 			locr0->v0 = rval[0];
-			locr0->v1 = rval[1];
 			locr0->a3 = 0;
 			break;
 
@@ -839,7 +838,6 @@ child_return(void *arg)
 
 	trapframe = p->p_md.md_regs;
 	trapframe->v0 = 0;
-	trapframe->v1 = 1;
 	trapframe->a3 = 0;
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/powerpc/powerpc/trap.c b/sys/arch/powerpc/powerpc/trap.c
index da68970686b..6c7e433e44d 100644
--- a/sys/arch/powerpc/powerpc/trap.c
+++ b/sys/arch/powerpc/powerpc/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.126 2022/10/22 00:58:56 gkoehler Exp $	*/
+/*	$OpenBSD: trap.c,v 1.127 2022/11/02 07:20:07 guenther Exp $	*/
 /*	$NetBSD: trap.c,v 1.3 1996/10/13 03:31:37 christos Exp $	*/
 
 /*
@@ -563,7 +563,6 @@ child_return(void *arg)
 
 	tf->fixreg[0] = 0;
 	tf->fixreg[FIRSTARG] = 0;
-	tf->fixreg[FIRSTARG + 1] = 1;
 	tf->cr &= ~0x10000000;
 	/* Disable FPU, VECT, as we can't be fpuproc */
 	tf->srr1 &= ~(PSL_FP|PSL_VEC);
diff --git a/sys/arch/powerpc64/powerpc64/syscall.c b/sys/arch/powerpc64/powerpc64/syscall.c
index 95fb92b5915..d47076d1824 100644
--- a/sys/arch/powerpc64/powerpc64/syscall.c
+++ b/sys/arch/powerpc64/powerpc64/syscall.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: syscall.c,v 1.8 2021/12/09 00:26:11 guenther Exp $	*/
+/*	$OpenBSD: syscall.c,v 1.9 2022/11/02 07:20:08 guenther Exp $	*/
 
 /*
  * Copyright (c) 2015 Dale Rahn <drahn@dalerahn.com>
@@ -64,7 +64,7 @@ syscall(struct trapframe *frame)
 	}
 
 	rval[0] = 0;
-	rval[1] = frame->fixreg[4];
+	rval[1] = 0;
 
 	error = mi_syscall(p, code, callp, args, rval);
 
@@ -72,7 +72,6 @@ syscall(struct trapframe *frame)
 	case 0:
 		frame->fixreg[0] = 0;
 		frame->fixreg[3] = rval[0];
-		frame->fixreg[4] = rval[1];
 		frame->cr &= ~0x10000000;
 		break;
 
@@ -102,7 +101,6 @@ child_return(void *arg)
 
 	frame->fixreg[0] = 0;
 	frame->fixreg[3] = 0;
-	frame->fixreg[4] = 1;
 	frame->cr &= ~0x10000000;
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/riscv64/riscv64/syscall.c b/sys/arch/riscv64/riscv64/syscall.c
index 81685bfd608..1e1b2ce6ed5 100644
--- a/sys/arch/riscv64/riscv64/syscall.c
+++ b/sys/arch/riscv64/riscv64/syscall.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: syscall.c,v 1.12 2022/02/22 13:34:23 visa Exp $	*/
+/*	$OpenBSD: syscall.c,v 1.13 2022/11/02 07:20:08 guenther Exp $	*/
 
 /*
  * Copyright (c) 2020 Brian Bamsch <bbamsch@google.com>
@@ -84,14 +84,13 @@ svc_handler(trapframe_t *frame)
 	}
 
 	rval[0] = 0;
-	rval[1] = frame->tf_a[1];
+	rval[1] = 0;
 
 	error = mi_syscall(p, code, callp, args, rval);
 
 	switch (error) {
 	case 0:
 		frame->tf_a[0] = rval[0];
-		frame->tf_a[1] = rval[1];
 		frame->tf_t[0] = 0;		/* syscall succeeded */
 		break;
 
@@ -119,7 +118,6 @@ child_return(void *arg)
 	struct trapframe *frame = process_frame(p);
 
 	frame->tf_a[0] = 0;
-	frame->tf_a[1] = 1;
 	frame->tf_t[0] = 0;			/* no error */
 
 	KERNEL_UNLOCK();
diff --git a/sys/arch/sparc64/sparc64/trap.c b/sys/arch/sparc64/sparc64/trap.c
index 540b0b48d72..8682eefb4be 100644
--- a/sys/arch/sparc64/sparc64/trap.c
+++ b/sys/arch/sparc64/sparc64/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.111 2022/10/21 18:55:42 miod Exp $	*/
+/*	$OpenBSD: trap.c,v 1.112 2022/11/02 07:20:08 guenther Exp $	*/
 /*	$NetBSD: trap.c,v 1.73 2001/08/09 01:03:01 eeh Exp $ */
 
 /*
@@ -1175,7 +1175,7 @@ syscall(struct trapframe *tf, register_t code, register_t pc)
 	}
 
 	rval[0] = 0;
-	rval[1] = tf->tf_out[1];
+	rval[1] = 0;
 
 	error = mi_syscall(p, code, callp, args, rval);
 
@@ -1184,7 +1184,6 @@ syscall(struct trapframe *tf, register_t code, register_t pc)
 	case 0:
 		/* Note: fork() does not return here in the child */
 		tf->tf_out[0] = rval[0];
-		tf->tf_out[1] = rval[1];
 		if (new) {
 			/* jmp %g2 on success */
 			dest = tf->tf_global[2];
@@ -1247,7 +1246,6 @@ child_return(void *arg)
 	 * Return values in the frame set by cpu_fork().
 	 */
 	tf->tf_out[0] = 0;
-	tf->tf_out[1] = 0;
 
 	KERNEL_UNLOCK();
 
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 4c3b5d071f3..e02a40aa4a4 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_fork.c,v 1.242 2022/08/14 01:58:27 jsg Exp $	*/
+/*	$OpenBSD: kern_fork.c,v 1.243 2022/11/02 07:20:07 guenther Exp $	*/
 /*	$NetBSD: kern_fork.c,v 1.29 1996/02/09 18:59:34 christos Exp $	*/
 
 /*
@@ -502,10 +502,8 @@ fork1(struct proc *curp, int flags, void (*func)(void *), void *arg,
 	/*
 	 * Return child pid to parent process
 	 */
-	if (retval != NULL) {
-		retval[0] = pr->ps_pid;
-		retval[1] = 0;
-	}
+	if (retval != NULL)
+		*retval = pr->ps_pid;
 	return (0);
 }
 
@@ -574,8 +572,7 @@ thread_fork(struct proc *curp, void *stack, void *tcb, pid_t *tidptr,
 	/*
 	 * Return tid to parent thread and copy it out to userspace
 	 */
-	retval[0] = tid = p->p_tid + THREAD_PID_OFFSET;
-	retval[1] = 0;
+	*retval = tid = p->p_tid + THREAD_PID_OFFSET;
 	if (tidptr != NULL) {
 		if (copyout(&tid, tidptr, sizeof(tid)))
 			psignal(curp, SIGSEGV);