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|
;
; Ullrich von Bassewitz, 19.03.2001
;
; 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 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
; 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, cstkchk
.constructor initstkchk, 25
.import __STACKSIZE__ ; Linker defined
.import pusha0, _exit
.importzp sp
; Use macros for better readability
.macpack generic
.macpack cpu
; ----------------------------------------------------------------------------
; Initialization code. This is a constructor, so it is called on startup if
; the linker has detected references to this module.
.segment "ONCE"
.proc initstkchk
lda sp
sta initialsp
sub #<__STACKSIZE__
sta lowwater
lda sp+1
sta initialsp+1
sbc #>__STACKSIZE__
.if (.cpu .bitand ::CPU_ISET_65SC02)
ina ; Add 256 bytes safety area
.else
add #1 ; Add 256 bytes safety area
.endif
sta lowwater+1
rts
.endproc
; ----------------------------------------------------------------------------
; 6502 stack checking routine. Does not need to save any registers.
; Safety zone for the hardware stack is 12 bytes.
.code
stkchk: tsx
cpx #12
bcc Fail ; Jump on stack overflow
rts ; Return if ok
; ----------------------------------------------------------------------------
; C stack checking routine. Does not need to save any registers.
.code
cstkchk:
; Check the high byte of the software stack
@L0: lda lowwater+1
cmp sp+1
bcs @L1
rts
; Check low byte
@L1: bne CStackOverflow
lda lowwater
cmp sp
bcs CStackOverflow
Done: rts
; We have a C stack overflow. Set the stack pointer to the initial value, so
; we can continue without worrying about stack issues.
CStackOverflow:
lda initialsp
sta sp
lda initialsp+1
sta sp+1
; 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
ldx #0
jmp _exit
; ----------------------------------------------------------------------------
; Data
.segment "INIT"
; Initial stack pointer value. Stack is reset to this in case of overflows to
; allow program exit processing.
initialsp: .res 2
; Stack low water mark.
lowwater: .res 2
|
