FA-89401 / Instruction set emulation / Open access

Return resumes at the pulled address · case 01

Execution returns onto the last byte of the call instruction.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

rts does not add one to the pulled return address.

VERIFIED REPAIR

Resume at pulled address + 1, wrapped to 16 bits.

Unsuccessful approach: Adding one without wrapping produces address 0x10000 at the top of memory.

Case contract

Input [pc, sp, ops] for an 8-bit stack pointer addressing page 0x100. push stores at 0x100+sp then decrements sp (wrapping in 8 bits); pull increments sp (wrapping) then reads (unwritten bytes read 0). jsr t (3 bytes at pc) pushes (pc+2) high byte then low byte and jumps; rts pulls low then high and resumes at that address + 1 (16-bit wrap). pha v pushes v, pla pulls; both and nop advance pc by 1. Return [[pc, sp, pulled value or None] per op, sorted [address, byte] of written stack memory].

Why this case matters

Emulated call/return must reproduce the exact stack image because programs inspect and manipulate return addresses on the stack.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    pc, sp, ops = args
    mem = {}
    trace = []
    def push(v):
        nonlocal sp
        mem[0x100 + sp] = v & 0xFF
        sp = (sp - 1) & 0xFF
    def pull():
        nonlocal sp
        sp = (sp + 1) & 0xFF
        return mem.get(0x100 + sp, 0)
    for op in ops:
        got = None
        if op[0] == 'jsr':
            ret = (pc + 2) & 0xFFFF
            push(ret >> 8)
            push(ret)
            pc = op[1]
        elif op[0] == 'rts':
            lo = pull()
            hi = pull()
            pc = (hi << 8 | lo)
        elif op[0] == 'pha':
            push(op[1])
            pc += 1
        elif op[0] == 'pla':
            got = pull()
            pc += 1
        else:
            pc += 1
        trace.append([pc, sp, got])
    return [trace, [[k, mem[k]] for k in sorted(mem)]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 18], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 86], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2289, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 129, [['jsr', 4660], ['rts']]], [[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 19], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 19]], [[510, 34], [511, 19]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 87], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 87]], [[256, 68], [257, 51], [511, 87]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2290, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2293, 255, None]], [[508, 2], [509, 9], [510, 244], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 130, [['jsr', 4660], ['rts']]], [[[4660, 128, None], [0, 130, None]], [[385, 255], [386, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 20], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 20]], [[510, 34], [511, 20]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 88], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 88]], [[256, 68], [257, 51], [511, 88]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2291, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2294, 255, None]], [[508, 2], [509, 9], [510, 245], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 131, [['jsr', 4660], ['rts']]], [[[4660, 129, None], [0, 131, None]], [[386, 255], [387, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 21], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 21]], [[510, 34], [511, 21]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 89], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 89]], [[256, 68], [257, 51], [511, 89]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2292, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2295, 255, None]], [[508, 2], [509, 9], [510, 246], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 132, [['jsr', 4660], ['rts']]], [[[4660, 130, None], [0, 132, None]], [[387, 255], [388, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 22], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 22]], [[510, 34], [511, 22]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 90], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 90]], [[256, 68], [257, 51], [511, 90]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2293, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2296, 255, None]], [[508, 2], [509, 9], [510, 247], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 133, [['jsr', 4660], ['rts']]], [[[4660, 131, None], [0, 133, None]], [[388, 255], [389, 255]]])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
call and return	`[[[1792, 251, None], [1793, 251, None], [1538, 253, None]], [[508, 2], [509, 6]]]`	`[[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]`	Failed
push and pull	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	Passed
stack pointer wraps below page start	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	Passed
pull wraps above page end	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	Passed
nested calls	`[[[2304, 253, None], [2560, 251, None], [2306, 253, None], [2291, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	`[[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	Failed
return address carries into high byte	`[[[8192, 238, None], [4352, 240, None]], [[495, 0], [496, 17]]]`	`[[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]`	Failed
return from top of memory	`[[[4660, 127, None], [65535, 129, None]], [[384, 255], [385, 255]]]`	`[[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]]`	Failed

SHA-256 / e5ca47a87b919f4d82db05d1f3081f4ee7205b1ca715e7f0c95623a24a9fb3c4

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    pc, sp, ops = args
    mem = {}
    trace = []
    def push(v):
        nonlocal sp
        mem[0x100 + sp] = v & 0xFF
        sp = (sp - 1) & 0xFF
    def pull():
        nonlocal sp
        sp = (sp + 1) & 0xFF
        return mem.get(0x100 + sp, 0)
    for op in ops:
        got = None
        if op[0] == 'jsr':
            ret = (pc + 2) & 0xFFFF
            push(ret >> 8)
            push(ret)
            pc = op[1]
        elif op[0] == 'rts':
            lo = pull()
            hi = pull()
            pc = (hi << 8 | lo) + 1
        elif op[0] == 'pha':
            push(op[1])
            pc += 1
        elif op[0] == 'pla':
            got = pull()
            pc += 1
        else:
            pc += 1
        trace.append([pc, sp, got])
    return [trace, [[k, mem[k]] for k in sorted(mem)]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 18], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 86], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2289, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 129, [['jsr', 4660], ['rts']]], [[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 19], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 19]], [[510, 34], [511, 19]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 87], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 87]], [[256, 68], [257, 51], [511, 87]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2290, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2293, 255, None]], [[508, 2], [509, 9], [510, 244], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 130, [['jsr', 4660], ['rts']]], [[[4660, 128, None], [0, 130, None]], [[385, 255], [386, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 20], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 20]], [[510, 34], [511, 20]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 88], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 88]], [[256, 68], [257, 51], [511, 88]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2291, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2294, 255, None]], [[508, 2], [509, 9], [510, 245], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 131, [['jsr', 4660], ['rts']]], [[[4660, 129, None], [0, 131, None]], [[386, 255], [387, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 21], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 21]], [[510, 34], [511, 21]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 89], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 89]], [[256, 68], [257, 51], [511, 89]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2292, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2295, 255, None]], [[508, 2], [509, 9], [510, 246], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 132, [['jsr', 4660], ['rts']]], [[[4660, 130, None], [0, 132, None]], [[387, 255], [388, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 22], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 22]], [[510, 34], [511, 22]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 90], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 90]], [[256, 68], [257, 51], [511, 90]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2293, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2296, 255, None]], [[508, 2], [509, 9], [510, 247], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 133, [['jsr', 4660], ['rts']]], [[[4660, 131, None], [0, 133, None]], [[388, 255], [389, 255]]])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
call and return	`[[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]`	`[[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]`	Passed
push and pull	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	Passed
stack pointer wraps below page start	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	Passed
pull wraps above page end	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	Passed
nested calls	`[[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	`[[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	Passed
return address carries into high byte	`[[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]`	`[[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]`	Passed
return from top of memory	`[[[4660, 127, None], [65536, 129, None]], [[384, 255], [385, 255]]]`	`[[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]]`	Failed

SHA-256 / fa1073820131d9cbdfe916f8819e6a68afcfc744f2dd9f583207e8c7c6c9e98e

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    pc, sp, ops = args
    mem = {}
    trace = []
    def push(v):
        nonlocal sp
        mem[0x100 + sp] = v & 0xFF
        sp = (sp - 1) & 0xFF
    def pull():
        nonlocal sp
        sp = (sp + 1) & 0xFF
        return mem.get(0x100 + sp, 0)
    for op in ops:
        got = None
        if op[0] == 'jsr':
            ret = (pc + 2) & 0xFFFF
            push(ret >> 8)
            push(ret)
            pc = op[1]
        elif op[0] == 'rts':
            lo = pull()
            hi = pull()
            pc = ((hi << 8 | lo) + 1) & 0xFFFF
        elif op[0] == 'pha':
            push(op[1])
            pc += 1
        elif op[0] == 'pla':
            got = pull()
            pc += 1
        else:
            pc += 1
        trace.append([pc, sp, got])
    return [trace, [[k, mem[k]] for k in sorted(mem)]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 18], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 86], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2289, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 129, [['jsr', 4660], ['rts']]], [[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 19], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 19]], [[510, 34], [511, 19]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 87], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 87]], [[256, 68], [257, 51], [511, 87]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2290, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2293, 255, None]], [[508, 2], [509, 9], [510, 244], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 130, [['jsr', 4660], ['rts']]], [[[4660, 128, None], [0, 130, None]], [[385, 255], [386, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 20], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 20]], [[510, 34], [511, 20]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 88], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 88]], [[256, 68], [257, 51], [511, 88]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2291, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2294, 255, None]], [[508, 2], [509, 9], [510, 245], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 131, [['jsr', 4660], ['rts']]], [[[4660, 129, None], [0, 131, None]], [[386, 255], [387, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 21], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 21]], [[510, 34], [511, 21]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 89], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 89]], [[256, 68], [257, 51], [511, 89]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2292, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2295, 255, None]], [[508, 2], [509, 9], [510, 246], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 132, [['jsr', 4660], ['rts']]], [[[4660, 130, None], [0, 132, None]], [[387, 255], [388, 255]]])], [('call and return', [1536, 253, [['jsr', 1792], ['nop'], ['rts']]], [[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]), ('push and pull', [512, 255, [['pha', 22], ['pha', 34], ['pla'], ['pla']]], [[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 22]], [[510, 34], [511, 22]]]), ('stack pointer wraps below page start', [768, 1, [['pha', 51], ['pha', 68], ['pha', 90], ['pla']]], [[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 90]], [[256, 68], [257, 51], [511, 90]]]), ('pull wraps above page end', [1024, 254, [['pla'], ['pla'], ['pla']]], [[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]), ('nested calls', [2293, 255, [['jsr', 2304], ['jsr', 2560], ['rts'], ['rts']]], [[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2296, 255, None]], [[508, 2], [509, 9], [510, 247], [511, 8]]]), ('return address carries into high byte', [4350, 240, [['jsr', 8192], ['rts']]], [[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]), ('return from top of memory', [65533, 133, [['jsr', 4660], ['rts']]], [[[4660, 131, None], [0, 133, None]], [[388, 255], [389, 255]]])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
call and return	`[[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]`	`[[[1792, 251, None], [1793, 251, None], [1539, 253, None]], [[508, 2], [509, 6]]]`	Passed
push and pull	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	`[[[513, 254, None], [514, 253, None], [515, 254, 34], [516, 255, 18]], [[510, 34], [511, 18]]]`	Passed
stack pointer wraps below page start	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	`[[[769, 0, None], [770, 255, None], [771, 254, None], [772, 255, 86]], [[256, 68], [257, 51], [511, 86]]]`	Passed
pull wraps above page end	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	`[[[1025, 255, 0], [1026, 0, 0], [1027, 1, 0]], []]`	Passed
nested calls	`[[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	`[[[2304, 253, None], [2560, 251, None], [2307, 253, None], [2292, 255, None]], [[508, 2], [509, 9], [510, 243], [511, 8]]]`	Passed
return address carries into high byte	`[[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]`	`[[[8192, 238, None], [4353, 240, None]], [[495, 0], [496, 17]]]`	Passed
return from top of memory	`[[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]]`	`[[[4660, 127, None], [0, 129, None]], [[384, 255], [385, 255]]]`	Passed

SHA-256 / e0b46f79f177f7411586b3f1799cbeb36c75e28fc35f0841f0668f6f994b36a4

Verification & scope

A deterministic bounded teaching model of one emulator rule; the instruction semantics are a stipulated contract inspired by common ISAs and are not a claim of cycle-exact or architectural conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:17.064481+00:00.

Case digest / bcc27ac3bec3b0567ca54f2a58a82a208d42dcd60221d87e5638c843ef95479e