Find limit of recursion: Difference between revisions
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=={{header|6502 Assembly}}==
The 6502's hardware stack isn't like other processors. First, it is fixed at the $0100-$01FF address range. The stack pointer is an 8-bit value, and assumes that the stack is always between $0100-$01FF. If the stack were to reach $01, and another <code>JSR</code> is executed, the stack would underflow to $FE, and the bottom of the stack would get clobbered. Since each JSR pushes a 2-byte return address onto the stack, the hardware limit of recursion is 128 calls.
Reading the current stack pointer is unreliable, as there is no requirement that the stack be "aligned" in any way. Unlike the 8086 and Z80, which require all pushes/pops to be exactly two bytes, the 6502's stack will likely contain both 1 byte registers and 2 byte return addresses. It's much easier to use a stack canary. Pick a value that is unlikely to be used in your program.
<lang 6502asm>
;beginning of your program
lda #$BE
sta $0100
lda #$EF
sta $0101
ldx #$ff
txs ;stack pointer is set to $FF
lda $0100 ;if this no longer equals $BE the stack has overflowed
cmp #$BE
bne StackHasOverflowed</lang>
=={{header|8080 Assembly}}==
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