a dumb possible fix for NetBSD PR Port-m68k/55990 https://gnats.netbsd.org/55990

m68k-setcontext-fix_20210220.diff

Index: m68k/reenter_syscall.s
===================================================================
RCS file: /cvsroot/src/sys/arch/m68k/m68k/reenter_syscall.s,v
retrieving revision 1.4
diff -u -p -d -r1.4 reenter_syscall.s
--- m68k/reenter_syscall.s	7 Sep 2013 19:06:29 -0000	1.4
+++ m68k/reenter_syscall.s	20 Feb 2021 01:38:49 -0000
@@ -6,6 +6,7 @@
  */
 
 #include <m68k/asm.h>
+#include "assym.h"
 
 /*
  * void reenter_syscall(struct frame *fp, int stkadj)
@@ -38,18 +39,31 @@ ENTRY_NOPROFILE(reenter_syscall)
 .Lcpfr:	movel	(%a0)+,(%a1)+
 	dbra	%d0,.Lcpfr
 
-	movew	%d1,%sp@(16*4+2)	| set stack adjust count
+	movew	%d1,%sp@(FR_ADJ)	| set stack adjust count
 	movel	(%sp),-(%sp)		| push syscall no (original d0 value)
 	jbsr	_C_LABEL(syscall)	| re-enter syscall()
 	addql	#4,%sp			| pop syscall no
 #ifdef DEBUG
-	tstw	%sp@(16*4+2)		| stack adjust must be zero
+	tstw	%sp@(FR_ADJ)		| stack adjust must be zero
 	jeq	.Ladjzero
 	PANIC("reenter_syscall")
 .Ladjzero:
 #endif
-	moveal	%sp@(15*4),%a0		| grab and restore
+	moveal	%sp@(FR_SP),%a0		| grab and restore
 	movel	%a0,%usp		|   user SP
+	movw	%sp@(FR_ADJ),%d0	| need to adjust stack?
+	jne	.Ladjstk		| yes, go to it
 	moveml	(%sp)+,#0x7FFF		| restore user registers
 	addql	#8,%sp			| pop SP and stack adjust
 	jra	_ASM_LABEL(rei)		| rte
+.Ladjstk:
+	lea	%sp@(FR_HW),%a1		| pointer to HW frame
+	addql	#8,%a1			| source pointer
+	movl	%a1,%a0			| source
+	addw	%d0,%a0			|  + hole size = dest pointer
+	movl	%a1@-,%a0@-		| copy
+	movl	%a1@-,%a0@-		|  8 bytes
+	movl	%a0,%sp@(FR_SP)		| new SSP
+	moveml	%sp@+,#0x7FFF		| restore user register
+	movl	%sp@,%sp		| and do real RTE
+	jra	_ASM_LABEL(rei)		| rte