65816-llvm-mos/tests/ubsan/README.md

tests/ubsan — UBSan-min smoke probe (Phase 6.2)

Nine-case probe that exercises the -fsanitize=undefined -fsanitize-minimal-runtime instrumentation end-to-end on the W65816 target:

Kind	UB	Sentinel
add-overflow	i16 INT_MAX + 1	$025000=0xC0DE
shift-out-of-bounds	u16 1 << 17	$025002=0xC0DF
divrem-overflow	i16 n / 0	$025004=0xC0E0
sub-overflow	i16 INT_MIN - 1	$025006=0xC0E1
mul-overflow	i16 INT_MAX * 2	$025008=0xC0E2
negate-overflow	i16 -INT_MIN	$02500A=0xC0E3
pointer-overflow	(char*)0xFFFFFFF0 + 0x40	$02500C=0xC0E4
load-invalid-value	_Bool loaded from byte = 2	$02500E=0xC0E5
out-of-bounds	arr[idx>=N] on static array	$025010=0xC0E6
(liveness)	tail of main reached	$025012=0xC0DA

The probe ships strong override defs for the nine __ubsan_handle_*_minimal recovering handlers it exercises; the remaining handlers are pulled in from runtime/ubsan.o so any extra UB site clang emits (e.g. constant- fold overflow at -O2) still resolves cleanly.

Build + run

bash tests/ubsan/runUbsanProbe.sh

Expected output:

MAME-READ addr=0x025000 val=0xc0de
MAME-READ addr=0x025002 val=0xc0df
MAME-READ addr=0x025004 val=0xc0e0
MAME-READ addr=0x025006 val=0xc0e1
MAME-READ addr=0x025008 val=0xc0e2
MAME-READ addr=0x02500a val=0xc0e3
MAME-READ addr=0x02500c val=0xc0e4
MAME-READ addr=0x02500e val=0xc0e5
MAME-READ addr=0x025010 val=0xc0e6
MAME-READ addr=0x025012 val=0xc0da
MAME OK: 10 reads matched

What this probe is NOT

• It is not a verification of the UBSan diagnostic format (the per-kind "ubsan: <kind> by 0x<pc>\n" line emitted by runtime/src/ubsan.c::reportError). The probe deliberately overrides the handlers so it can verify the call edge without pulling in console code. A separate diagnostic-format probe would link libc.o + libcGno.o + GNO crt0 and assert on stderr.
• It is not a sweep of all 25 handler kinds. The kinds covered are all the cheap-to-trigger recoverable handlers that clang emits at -O2 for the W65816 target. Aborting-only kinds (e.g. builtin_unreachable_minimal, missing_return_minimal) cannot be exercised here because returning from the handler after the IR unreachable is itself UB. Float-cast-overflow / VLA-not-positive / type-mismatch / CFI / Objective-C kinds are linked but not triggered.

Files

• ubsanProbe.c — the probe itself
• build.sh — compiles with -fsanitize=undefined -fsanitize-minimal-runtime
• runUbsanProbe.sh — build + link + run under MAME with --check
• ubsanProbe.manifest.json — segment layout + check sentinel descriptor