Added a stack checking routine

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

diff --git a/libsrc/runtime/Makefile b/libsrc/runtime/Makefile
index febeb68f4e7c38d601cc3a63bdde1acd6421cf87..beaab454cc768a39ccae56c28d8fe78407bf5962 100644 (file)
--- a/libsrc/runtime/Makefile
+++ b/libsrc/runtime/Makefile
@@ -164,6 +164,7 @@ OBJS =      add.o           \
        staxspp.o       \
                steaxsp.o       \
        steaxspp.o      \
+       stkchk.o        \
                sub.o           \
                subeqsp.o       \
        subysp.o        \

diff --git a/libsrc/runtime/stkchk.s b/libsrc/runtime/stkchk.s
new file mode 100644 (file)
index 0000000..be4c294
--- /dev/null
+++ b/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
+
+