Added code to check the 6502 stack

git-svn-id: svn://svn.cc65.org/cc65/trunk@638 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/runtime/stkchk.s

@@ -1,9 +1,10 @@
 ;
 ; Ullrich von Bassewitz, 19.03.2001
 ;
-; Stack checking code.
+; Stack checking code. These are actually two routines, one to check the C
+; stack, and the other one to check the 6502 hardware stack.
 ; For performance reasons (to avoid having to pass a parameter), the compiler
-; calls the stkchk routine *after* allocating space on the stack. So the
+; calls the cstkchk 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
@@ -12,7 +13,7 @@
 ; its' bounds.
 ;
 
- 	.export	 	stkchk
+ 	.export	 	stkchk, cstkchk
  	.constructor	initstkchk, 25
 	.import	 	__STACKSIZE__			; Linker defined
        	.import	       	pusha0, _exit
@@ -29,51 +30,64 @@
 
 .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
+	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.
+; 6502 stack checking routine. Does not need to save any registers.
+; Safety zone for the hardware stack is 10 bytes.
 
-.proc	stkchk
+stkchk:	tsx
+       	cpx  	#10
+       	bcc    	Fail	     	; Jump on stack overflow
+	rts			; Return if ok
 
-	lda	lowwater+1
-	cmp	sp+1
-	bcs    	@L1
-	rts
+; ----------------------------------------------------------------------------
+; C stack checking routine. Does not need to save any registers.
+
+cstkchk:
+
+; Check the high byte of the software stack
+
+@L0:   	lda  	lowwater+1
+       	cmp  	sp+1
+       	bcs    	@L1
+       	rts
 
 ; Check low byte
 
-@L1:	bne	@Overflow
-	lda	lowwater
-	cmp	sp
-	bcs	@Overflow
-	rts
+@L1: 	bne	CStackOverflow
+     	lda	lowwater
+     	cmp	sp
+      	bcs	CStackOverflow
+Done: 	rts
 
-; We have a stack overflow. Set the stack pointer to the initial value, so
+; We have a C stack overflow. Set the stack pointer to the initial value, so
 ; we can continue without worrying about stack issues.
 
-@Overflow:
+CStackOverflow:
 	lda	initialsp
 	sta	sp
 	lda	initialsp+1
 	sta	sp+1
- 	lda	#4
+
+; Generic abort entry. We should output a diagnostic here, but this is
+; difficult, since we're operating at a lower level here.
+
+Fail:	lda	#4
  	jsr	pusha0
  	jmp	_exit
 
-.endproc
-
 ; ----------------------------------------------------------------------------
 ; Data