java-topology/defects/vice-0001/test/ViceMonitorBreakpointTest.java

import java.util.*;

/**
 * Unit test for VICE CWE-407 defect vice-0001.
 *
 * vice-0001: search_checkpoint_list in mon_breakpoint.c traverses the
 * entire sorted checkpoint linked list O(N) per memory access even though
 * the list is kept in ascending start_addr order.  The code comment says
 * "we can drop out early" but never implements the early exit.
 *
 * Models the C linked-list scan and demonstrates the O(1)/O(log N) fix
 * by adding a single guard: if entry.start > target, break immediately.
 */
public class ViceMonitorBreakpointTest {

    /** Represents one checkpoint (breakpoint/watchpoint). */
    static class Checkpoint {
        int start_addr;
        int end_addr;

        Checkpoint(int start, int end) {
            this.start_addr = start;
            this.end_addr = end;
        }
    }

    // ---------------------------------------------------------------
    // DEFECTIVE: O(N) scan — no early exit even though list is sorted
    // ---------------------------------------------------------------

    /**
     * Models search_checkpoint_list as written: walks every node.
     * Returns true if any checkpoint covers addr.
     */
    static int[] defective_search(List<Checkpoint> sortedList, int addr) {
        int comparisons = 0;
        for (Checkpoint cp : sortedList) {
            comparisons++;
            if (addr >= cp.start_addr && addr <= cp.end_addr) {
                return new int[]{1, comparisons}; // found, comparisons
            }
        }
        return new int[]{0, comparisons}; // not found, comparisons
    }

    // ---------------------------------------------------------------
    // FIXED: early exit when entry.start_addr > addr (sorted invariant)
    // ---------------------------------------------------------------

    /**
     * Models the patched search_checkpoint_list.
     * Breaks as soon as entry.start_addr > addr.
     */
    static int[] fixed_search(List<Checkpoint> sortedList, int addr) {
        int comparisons = 0;
        for (Checkpoint cp : sortedList) {
            comparisons++;
            if (cp.start_addr > addr) {
                break; // sorted list: no further match possible
            }
            if (addr >= cp.start_addr && addr <= cp.end_addr) {
                return new int[]{1, comparisons}; // found
            }
        }
        return new int[]{0, comparisons}; // not found
    }

    // ---------------------------------------------------------------
    // Build a sorted list of N single-address breakpoints
    // ---------------------------------------------------------------

    static List<Checkpoint> buildSortedBreakpoints(int n) {
        List<Checkpoint> list = new ArrayList<>();
        // Breakpoints at even addresses: 0x0100, 0x0102, ... step 2
        for (int i = 0; i < n; i++) {
            int addr = 0x0100 + i * 2;
            list.add(new Checkpoint(addr, addr));
        }
        return list;
    }

    // ---------------------------------------------------------------
    // Tests
    // ---------------------------------------------------------------

    static int passed = 0;
    static int failed = 0;

    static void check(String name, boolean condition) {
        if (condition) {
            System.out.println("PASS " + name);
            passed++;
        } else {
            System.out.println("FAIL " + name);
            failed++;
        }
    }

    public static void main(String[] args) {

        // --- Correctness ---

        List<Checkpoint> bps = buildSortedBreakpoints(10);
        // Addr 0x0100 is our first breakpoint
        int[] r1d = defective_search(bps, 0x0100);
        int[] r1f = fixed_search(bps, 0x0100);
        check("vice-0001 correctness: found first breakpoint (defective)",  r1d[0] == 1);
        check("vice-0001 correctness: found first breakpoint (fixed)",      r1f[0] == 1);

        // Addr 0x0112 = 0x0100 + 9*2 = last breakpoint
        int[] r2d = defective_search(bps, 0x0112);
        int[] r2f = fixed_search(bps, 0x0112);
        check("vice-0001 correctness: found last breakpoint (defective)",   r2d[0] == 1);
        check("vice-0001 correctness: found last breakpoint (fixed)",       r2f[0] == 1);

        // Addr 0x0050 is below all breakpoints — miss
        int[] r3d = defective_search(bps, 0x0050);
        int[] r3f = fixed_search(bps, 0x0050);
        check("vice-0001 correctness: miss below range (defective)",        r3d[0] == 0);
        check("vice-0001 correctness: miss below range (fixed)",            r3f[0] == 0);
        // defective must scan all 10; fixed exits on first entry (start 0x0100 > 0x0050)
        check("vice-0001 correctness: fixed exits after 1 comparison on miss below range",
              r3f[1] == 1);
        check("vice-0001 correctness: defective scans all N on miss below range",
              r3d[1] == 10);

        // Addr 0x8000 is above all breakpoints — miss
        int[] r4d = defective_search(bps, 0x8000);
        int[] r4f = fixed_search(bps, 0x8000);
        check("vice-0001 correctness: miss above range (defective)",        r4d[0] == 0);
        check("vice-0001 correctness: miss above range (fixed)",            r4f[0] == 0);

        // --- Performance: measure total comparisons at N=200 breakpoints ---
        int N = 200;
        List<Checkpoint> bigBps = buildSortedBreakpoints(N);

        // Simulate M consecutive opcode checks at addresses mostly BELOW the
        // first breakpoint (common case: code running without hitting any bp).
        int M = 10_000;
        long defectiveTotal = 0;
        long fixedTotal = 0;

        // Also measure real wall time
        long t0 = System.currentTimeMillis();
        for (int i = 0; i < M; i++) {
            int[] r = defective_search(bigBps, 0x0050 + (i % 16));
            defectiveTotal += r[1];
        }
        long defTime = System.currentTimeMillis() - t0;

        t0 = System.currentTimeMillis();
        for (int i = 0; i < M; i++) {
            int[] r = fixed_search(bigBps, 0x0050 + (i % 16));
            fixedTotal += r[1];
        }
        long fixTime = System.currentTimeMillis() - t0;

        // defective: N comparisons per miss; fixed: 1 comparison per miss
        double ratio = (fixedTotal == 0) ? Double.MAX_VALUE : (double) defectiveTotal / fixedTotal;
        System.out.printf(
            "vice-0001 performance: N=%d M=%d defect_cmps=%d fixed_cmps=%d ratio=%.1fx%n",
            N, M, defectiveTotal, fixedTotal, ratio);

        // Expect at least N/4 speedup for below-range misses
        check("vice-0001 performance: fixed comparison count <= defective/N",
              fixedTotal * N <= defectiveTotal * 2);

        System.out.printf("%n%d/%d tests passed%n", passed, passed + failed);
        if (failed > 0) System.exit(1);
    }
}