Added a stack checking routine

git-svn-id: svn://svn.cc65.org/cc65/trunk@627 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/runtime/Makefile

@@ -164,6 +164,7 @@ OBJS = 	add.o		\
 	staxspp.o	\
        	steaxsp.o	\
 	steaxspp.o	\
+	stkchk.o	\
        	sub.o		\
        	subeqsp.o	\
 	subysp.o	\

libsrc/runtime/stkchk.s

@@ -0,0 +1,86 @@
+;
+; Ullrich von Bassewitz, 19.03.2001
+;
+; Stack checking code.
+; For performance reasons (to avoid having to pass a parameter), the compiler
+; calls the stkchk routine *after* allocating space on the stack. So the
+; stackpointer may already be invalid if this routine is called. In addition
+; to that, pushs and pops that are needed for expression evaluation are not
+; checked (this would be way too much overhead). As a consequence we will
+; operate using a safety area at the stack bottom. Once the stack reaches this
+; safety area, we consider it an overflow, even if the stack is still inside
+; its' bounds.
+;
+
+ 	.export		stkchk
+ 	.constructor	initstkchk, 25
+	.import		__STACKSIZE__			; Linker defined
+       	.import	       	pusha0, exit
+ 	.importzp	sp
+
+	; Use macros for better readability
+	.macpack	generic
+
+.code
+
+; ----------------------------------------------------------------------------
+; Initialization code. This is a constructor, so it is called on startup if
+; the linker has detected references to this module.
+
+.proc	initstkchk
+
+	lda	sp
+	sta	initialsp
+	sub	#<__STACKSIZE__
+	sta	lowwater
+	lda	sp+1
+	sta	initialsp+1
+	sbc	#>__STACKSIZE__
+	add	#1	 		; Add 256 bytes safety area
+	sta	lowwater+1
+	rts
+
+.endproc
+
+; ----------------------------------------------------------------------------
+; Stack checking routine. Does not need to save any registers.
+
+.proc	stkchk
+
+	lda	lowwater+1
+	cmp	sp+1
+	bcs    	@L1
+	rts
+
+; Check low byte
+
+@L1:	bne	@Overflow
+	lda	lowwater
+	cmp	sp
+	bcs	@Overflow
+	rts
+
+; We have a stack overflow. Set the stack pointer to the low water mark, so
+; we have
+
+@Overflow:
+ 	lda	#4
+ 	jsr	pusha0
+ 	jmp	exit
+
+
+.endproc
+
+; ----------------------------------------------------------------------------
+; Data
+
+.bss
+
+; Initial stack pointer value. Stack is reset to this in case of overflows to
+; allow program exit processing.
+initialsp: 	.word	0
+
+; Stack low water mark.
+lowwater:  	.word	0
+
+