Add fuzz_test.sh: a long-running gdb-driven fuzz loop over cross_sectional_200k.ep_

Documents two build/invocation bugs hit getting this working: DEBUG builds
need MP=1 too or --cpus is silently unrecognized, and gdb's
"handle SIGTRAP nostop noprint pass" breaks thread control against the
MP/pthread binary (misdiagnosed at first as a sandboxed ptrace restriction,
but reproduces outside any harness and goes away once that directive is
dropped).

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 73 insertions, 0 deletions

diff --git a/src/fuzz_test.sh b/src/fuzz_test.sh
new file mode 100755
index 0000000..5e3d5f7
--- /dev/null
+++ b/src/fuzz_test.sh
@@ -0,0 +1,73 @@
+#!/bin/sh
+# Long-running fuzz loop per TESTING_PLAN.md's "Fuzz testing" section:
+# repeatedly draw a fresh random batch of setboard/go records from the full
+# 200k-position tests/cross_sectional_200k.ep_ pool, run them through a
+# DEBUG=1 build under gdb (so any assert/SIGTRAP/SIGSEGV leaves a full
+# backtrace instead of just a bare crash), shallow-depth, small/no hash
+# (setboard memsets the hash table as a side effect, so a large --hash
+# wastes time on every single record), --cpus 2 to exercise split.c's
+# parallel search path too. Runs until stopped (^C) or a crash is found.
+#
+# Usage: ./fuzz_test.sh [binary] [depth] [batch_size] [cpus]
+
+BIN="${1:-./_typhoon}"
+DEPTH="${2:-6}"
+BATCH="${3:-200}"
+CPUS="${4:-2}"
+SUITE=../tests/cross_sectional_200k.ep_
+LOGDIR=/usr/local/tmp/typhoon/fuzz
+mkdir -p "$LOGDIR"
+
+if [ ! -x "$BIN" ]; then
+    echo "ERROR: $BIN not found/executable (build first: gmake clean; gmake DEBUG=1 MP=1)"
+    exit 1
+fi
+if [ ! -f "$SUITE" ]; then
+    echo "ERROR: $SUITE not found (run from src/)"
+    exit 1
+fi
+
+TOTAL_RECORDS=$(grep -c '^go' "$SUITE")
+
+ITER=0
+while :; do
+    ITER=$((ITER + 1))
+    SAMPLE="$LOGDIR/batch_${ITER}.ep_"
+    awk -v k="$BATCH" -v n="$TOTAL_RECORDS" 'BEGIN { srand() }
+        { sub(/\r$/, "") }
+        /^setboard/ { rec = $0; next }
+        /^go[ \t]*$/ { rec = rec "\n" $0; c++; recs[c] = rec; rec = ""; next }
+        rec != "" { rec = rec "\n" $0 }
+        END {
+            picked = 0
+            while (picked < k && picked < c) {
+                r = int(rand() * c) + 1
+                if (!(r in used)) { used[r] = 1; print recs[r]; picked++ }
+            }
+        }' "$SUITE" > "$SAMPLE"
+
+    STAMP=$(date +%Y%m%d_%H%M%S)
+    LOG="$LOGDIR/run_${ITER}_${STAMP}.log"
+    GDBOUT="$LOGDIR/run_${ITER}_${STAMP}.gdb.txt"
+
+    echo "=== iter $ITER: $BATCH positions from $SUITE (sd $DEPTH, cpus $CPUS) -> $GDBOUT ==="
+
+    gdb -q -batch \
+        -ex "set pagination off" \
+        -ex run \
+        -ex "bt full" \
+        -ex "info registers" \
+        --args "$BIN" --cpus "$CPUS" --hash 1m --logfile "$LOG" \
+            --batch --command "force; book name /nonexistent.book.bin; sd $DEPTH; script $SAMPLE" \
+        > "$GDBOUT" 2>&1
+    STATUS=$?
+
+    if grep -qE 'Program terminated with signal (SIGSEGV|SIGABRT|SIGBUS|SIGILL|SIGFPE)|Assertion failure' "$GDBOUT"; then
+        echo "*** CRASH/ASSERT DETECTED on iter $ITER -- see $GDBOUT ***"
+        echo "    positions: $SAMPLE"
+        echo "    engine log: $LOG"
+        exit 1
+    fi
+
+    echo "    iter $ITER clean (exit=$STATUS)"
+done