runtime: fix openbsd/386

In revision 05c3fee13eb3, openbsd/386's tfork implementation was
accidentally changed in one instruction from using the "params"
parameter to using the "psize" parameter.

While here, OpenBSD's __tfork system call returns a pid_t which is an
int32 on all OpenBSD architectures, so change runtime.tfork's return
type from int64 to int32 and update the assembly implementations
accordingly.

LGTM=iant
R=rsc, iant
CC=golang-codereviews, jsing
https://golang.org/cl/133190043

src/pkg/runtime/os_openbsd.c

@@ -26,7 +26,7 @@ extern SigTab runtime·sigtab[];
 static Sigset sigset_none;
 static Sigset sigset_all = ~(Sigset)0;
 
-extern int64 runtime·tfork(void *param, uintptr psize, M *mp, G *gp, void (*fn)(void));
+extern int32 runtime·tfork(void *param, uintptr psize, M *mp, G *gp, void (*fn)(void));
 extern int32 runtime·thrsleep(void *ident, int32 clock_id, void *tsp, void *lock, const int32 *abort);
 extern int32 runtime·thrwakeup(void *ident, int32 n);
 

src/pkg/runtime/os_openbsd.go

@@ -15,6 +15,6 @@ func raise(sig int32)
 func kqueue() int32
 func kevent(fd int32, ev1 unsafe.Pointer, nev1 int32, ev2 unsafe.Pointer, nev2 int32, ts unsafe.Pointer) int32
 func closeonexec(fd int32)
-func tfork(param unsafe.Pointer, psize uintptr, mm, gg, fn unsafe.Pointer) int64
+func tfork(param unsafe.Pointer, psize uintptr, mm, gg, fn unsafe.Pointer) int32
 func thrsleep(ident unsafe.Pointer, clock_id int32, tsp, lock, abort unsafe.Pointer) int32
 func thrwakeup(ident unsafe.Pointer, n int32) int32

src/pkg/runtime/sys_openbsd_386.s

@@ -226,7 +226,7 @@ sigtramp_ret:
 TEXT runtime·tfork(SB),NOSPLIT,$12
 
 	// Copy mp, gp and fn from the parent stack onto the child stack.
-	MOVL	psize+4(FP), AX
+	MOVL	param+0(FP), AX
 	MOVL	8(AX), CX		// tf_stack
 	SUBL	$16, CX
 	MOVL	CX, 8(AX)
@@ -247,17 +247,15 @@ TEXT runtime·tfork(SB),NOSPLIT,$12
 	INT	$0x80
 
 	// Return if tfork syscall failed.
-	JCC	5(PC)
+	JCC	4(PC)
 	NEGL	AX
-	MOVL	AX, ret_lo+20(FP)
-	MOVL	$-1, ret_hi+24(FP)
+	MOVL	AX, ret+20(FP)
 	RET
 
 	// In parent, return.
 	CMPL	AX, $0
-	JEQ	4(PC)
-	MOVL	AX, ret_lo+20(FP)
-	MOVL	$0, ret_hi+24(FP)
+	JEQ	3(PC)
+	MOVL	AX, ret+20(FP)
 	RET
 
 	// Paranoia: check that SP is as we expect.

src/pkg/runtime/sys_openbsd_amd64.s

@@ -11,7 +11,7 @@
 
 #define CLOCK_MONOTONIC	$3
 
-// int64 tfork(void *param, uintptr psize, M *mp, G *gp, void (*fn)(void));
+// int32 tfork(void *param, uintptr psize, M *mp, G *gp, void (*fn)(void));
 TEXT runtime·tfork(SB),NOSPLIT,$32
 
 	// Copy mp, gp and fn off parent stack for use by child.
@@ -27,13 +27,13 @@ TEXT runtime·tfork(SB),NOSPLIT,$32
 	// Return if tfork syscall failed.
 	JCC	4(PC)
 	NEGQ	AX
-	MOVQ	AX, ret+40(FP)
+	MOVL	AX, ret+40(FP)
 	RET
 
 	// In parent, return.
 	CMPL	AX, $0
 	JEQ	3(PC)
-	MOVQ	AX, ret+40(FP)
+	MOVL	AX, ret+40(FP)
 	RET
 
 	// Set FS to point at m->tls.