Fuzz replay

actions/cairn-zig-fuzz-afl/action.yml

@@ -1,5 +1,5 @@
 name: 'Cairn Zig Fuzz (AFL++)'
-description: 'Build and run Zig AFL++ fuzz targets, reporting crashes and corpus to Cairn. Each target is built via `zig build fuzz -Dfuzz-target=<name>`.'
+description: 'Build and run Zig AFL++ fuzz targets, reporting crashes and corpus to Cairn. Each target is built twice: `zig build fuzz -Dfuzz-target=<name>` (AFL-instrumented) and `zig build fuzz-replay -Dfuzz-target=<name>` (plain, for crash replay).'
 
 inputs:
   cairn_server:
@@ -115,7 +115,30 @@ runs:
         echo "Building ${TARGET_COUNT} target(s)"
         echo "=========================================="
 
+        # Helper to find the single executable in a bin/ directory.
+        find_bin() {
+          local BIN_DIR="$1"
+          local LABEL="$2"
+          if [ -n "${FUZZ_BINARY}" ]; then
+            echo "${BIN_DIR}/${FUZZ_BINARY}"
+            return
+          fi
+          local BIN
+          BIN=$(find "${BIN_DIR}" -maxdepth 1 -type f -executable)
+          local COUNT
+          COUNT=$(echo "${BIN}" | wc -l)
+          if [ "${COUNT}" -eq 0 ] || [ -z "${BIN}" ]; then
+            echo "ERROR: No executable found in ${BIN_DIR} (${LABEL})" >&2
+            return 1
+          elif [ "${COUNT}" -gt 1 ]; then
+            echo "ERROR: Multiple executables in ${BIN_DIR} (${LABEL}), specify fuzz_binary input" >&2
+            return 1
+          fi
+          echo "${BIN}"
+        }
+
         declare -A TARGET_BINS
+        declare -A REPLAY_BINS
         for i in "${!TARGET_NAMES[@]}"; do
           FUZZ_TARGET="${TARGET_NAMES[$i]}"
           NUM=$((i + 1))
@@ -124,33 +147,32 @@ runs:
 
           echo "[${NUM}/${TARGET_COUNT}] Building ${FUZZ_TARGET}..."
 
-          # Each target gets its own zig-out to avoid binary name collisions.
+          # Each target gets its own output dir to avoid binary name collisions.
-          ZIG_OUT="${WORK}/zig-out"
+          # 1) AFL-instrumented binary for fuzzing.
-          rm -rf "${ZIG_OUT}"
+          AFL_OUT="${WORK}/afl-out"
-          zig build fuzz -Dfuzz-target="${FUZZ_TARGET}" --prefix "${ZIG_OUT}"
+          rm -rf "${AFL_OUT}"
-
+          zig build fuzz -Dfuzz-target="${FUZZ_TARGET}" --prefix "${AFL_OUT}"
-          # Locate fuzz binary.
-          if [ -n "${FUZZ_BINARY}" ]; then
-            FUZZ_BIN="${ZIG_OUT}/bin/${FUZZ_BINARY}"
-          else
-            FUZZ_BIN=$(find "${ZIG_OUT}/bin" -maxdepth 1 -type f -executable)
-            BIN_COUNT=$(echo "${FUZZ_BIN}" | wc -l)
-            if [ "${BIN_COUNT}" -eq 0 ] || [ -z "${FUZZ_BIN}" ]; then
-              echo "ERROR: No executable found in ${ZIG_OUT}/bin/"
-              exit 1
-            elif [ "${BIN_COUNT}" -gt 1 ]; then
-              echo "ERROR: Multiple executables in ${ZIG_OUT}/bin/, specify fuzz_binary input"
-              exit 1
-            fi
-          fi
 
+          FUZZ_BIN=$(find_bin "${AFL_OUT}/bin" "afl")
           if [ ! -x "${FUZZ_BIN}" ]; then
             echo "ERROR: Fuzz binary not found or not executable: ${FUZZ_BIN}"
             exit 1
           fi
-
           TARGET_BINS["${FUZZ_TARGET}"]="${FUZZ_BIN}"
-          echo "  Built: ${FUZZ_BIN}"
+          echo "  AFL binary: ${FUZZ_BIN}"
+
+          # 2) Plain binary for crash replay (no AFL instrumentation).
+          REPLAY_OUT="${WORK}/replay-out"
+          rm -rf "${REPLAY_OUT}"
+          zig build fuzz-replay -Dfuzz-target="${FUZZ_TARGET}" --prefix "${REPLAY_OUT}"
+
+          REPLAY_BIN=$(find_bin "${REPLAY_OUT}/bin" "replay")
+          if [ ! -x "${REPLAY_BIN}" ]; then
+            echo "ERROR: Replay binary not found or not executable: ${REPLAY_BIN}"
+            exit 1
+          fi
+          REPLAY_BINS["${FUZZ_TARGET}"]="${REPLAY_BIN}"
+          echo "  Replay binary: ${REPLAY_BIN}"
         done
 
         # ── Phase 2: Prepare seeds and Cairn targets (sequential, network I/O) ──
@@ -326,6 +348,7 @@ runs:
           FUZZ_TARGET="${TARGET_NAMES[$i]}"
           NUM=$((i + 1))
           FUZZ_BIN="${TARGET_BINS[${FUZZ_TARGET}]}"
+          REPLAY_BIN="${REPLAY_BINS[${FUZZ_TARGET}]}"
           RUN_ID="${RUN_IDS[${FUZZ_TARGET}]}"
           CAIRN_TARGET_ID="${CAIRN_TARGET_IDS[${FUZZ_TARGET}]}"
           FINDINGS="work/${FUZZ_TARGET}/findings"
@@ -346,16 +369,20 @@ runs:
                   ;;
               esac
 
-              # Replay the crash input to capture the stack trace.
+              # Replay using the non-AFL binary to get a proper stack trace.
               STACK_TRACE=""
               CRASH_MSG="AFL++ crash (${FUZZ_TARGET}): ${CRASH_NAME}"
-              REPLAY_OUTPUT=$(timeout 10 "${FUZZ_BIN}" < "${crash_file}" 2>&1 || true)
+              REPLAY_OUTPUT=$(timeout 10 "${REPLAY_BIN}" < "${crash_file}" 2>&1 || true)
               if [ -n "${REPLAY_OUTPUT}" ]; then
                 STACK_TRACE="${REPLAY_OUTPUT}"
                 FIRST_LINE=$(echo "${REPLAY_OUTPUT}" | grep -m1 -iE 'panic|error|fault|abort|overflow|undefined|sanitizer|SUMMARY' || true)
                 if [ -n "${FIRST_LINE}" ]; then
                   CRASH_MSG="${FIRST_LINE}"
                 fi
+                echo "  Replay (${CRASH_NAME}):"
+                echo "${REPLAY_OUTPUT}" | head -10 | sed 's/^/    /'
+              else
+                echo "  Replay produced no output for ${CRASH_NAME}"
               fi
 
               echo "  Uploading crash: ${CRASH_NAME}"