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110 lines
2.7 KiB
ArmAsm
110 lines
2.7 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 19.03.2001
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;
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; Stack checking code. These are actually two routines, one to check the C
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; stack, and the other one to check the 6502 hardware stack.
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; For performance reasons (to avoid having to pass a parameter), the compiler
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; calls the cstkchk routine *after* allocating space on the stack. So the
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; stackpointer may already be invalid if this routine is called. In addition
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; to that, pushs and pops that are needed for expression evaluation are not
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; checked (this would be way too much overhead). As a consequence we will
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; operate using a safety area at the stack bottom. Once the stack reaches this
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; safety area, we consider it an overflow, even if the stack is still inside
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; its' bounds.
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;
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.export stkchk, cstkchk
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.constructor initstkchk, 25
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.import __STACKSIZE__ ; Linker defined
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.import pusha0, _exit
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.importzp sp
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; Use macros for better readability
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.macpack generic
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; ----------------------------------------------------------------------------
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; Initialization code. This is a constructor, so it is called on startup if
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; the linker has detected references to this module.
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.segment "INIT"
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.proc initstkchk
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lda sp
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sta initialsp
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sub #<__STACKSIZE__
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sta lowwater
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lda sp+1
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sta initialsp+1
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sbc #>__STACKSIZE__
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add #1 ; Add 256 bytes safety area
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sta lowwater+1
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rts
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.endproc
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; ----------------------------------------------------------------------------
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; 6502 stack checking routine. Does not need to save any registers.
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; Safety zone for the hardware stack is 12 bytes.
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.code
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stkchk: tsx
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cpx #12
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bcc Fail ; Jump on stack overflow
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rts ; Return if ok
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; ----------------------------------------------------------------------------
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; C stack checking routine. Does not need to save any registers.
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.code
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cstkchk:
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; Check the high byte of the software stack
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@L0: lda lowwater+1
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cmp sp+1
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bcs @L1
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rts
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; Check low byte
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@L1: bne CStackOverflow
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lda lowwater
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cmp sp
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bcs CStackOverflow
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Done: rts
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; We have a C stack overflow. Set the stack pointer to the initial value, so
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; we can continue without worrying about stack issues.
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CStackOverflow:
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lda initialsp
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sta sp
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lda initialsp+1
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sta sp+1
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; Generic abort entry. We should output a diagnostic here, but this is
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; difficult, since we're operating at a lower level here.
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Fail: lda #4
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ldx #0
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jmp _exit
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; ----------------------------------------------------------------------------
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; Data
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.bss
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; Initial stack pointer value. Stack is reset to this in case of overflows to
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; allow program exit processing.
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initialsp: .word 0
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; Stack low water mark.
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lowwater: .word 0
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