russell@unturf.com
0a580b313d
Authors: russell@unturf.com · brackishbert@gmail.com · foxhop.net · TimeHexOn.com Patches, unit tests, benchmarks, whitepaper, and outreach briefs. Public domain — no copyright claimed. Use freely.
415 lines
11 KiB
ReStructuredText
415 lines
11 KiB
ReStructuredText
javac — CWE-407 Analysis
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========================
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.. contents:: :local:
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Overview
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--------
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``javac`` is the Java compiler shipped as part of OpenJDK, the reference implementation of the
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Java platform. It performs type inference, annotation processing, and dependency analysis —
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all of which require graph traversal over type-variable graphs and compilation-unit dependency
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graphs. Five CWE-407 defect sites were found across four source files in the
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``com.sun.tools.javac`` package. All five have been patched.
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Defect Sites
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------------
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javac-0001
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~~~~~~~~~~
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**File:** ``src/jdk.compiler/share/classes/com/sun/tools/javac/util/GraphUtils.java:186``
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**Pattern:**
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.. code-block:: java
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// Tarjan SCC — onStack membership test
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while (!stack.isEmpty()) {
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Node n = stack.peek();
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if (n.lowlink == n.index) break;
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stack.pop();
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if (stack.contains(n)) { // O(V) linear scan every iteration
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...
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}
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}
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**Why this is O(n):** ``stack`` is an ``ArrayDeque``; ``contains()`` walks every element.
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**Complexity:** ``O(V²)`` where V = number of nodes in the strongly connected component
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**Patch:**
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.. code-block:: java
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// Replace ArrayDeque membership test with a boolean flag on the node
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n.active = true; // set when pushed
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n.active = false; // clear when popped
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// membership test: if (n.active) { ... }
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**Data structure change:** ``ArrayDeque<Node> stack`` membership test → ``boolean Node.active`` flag
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**Status:** Patched
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Benchmark Results
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-----------------
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.. list-table::
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:header-rows: 1
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* - V (nodes)
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- Before (ops)
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- After (ops)
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- Speedup
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* - 200
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- 20,100
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- 199
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- ~101x (op count); 60,040 ns → 7,428 ns (~8x wall)
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* - 800
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- 320,400
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- 799
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- ~401x (op count); 703,732 ns → 30,736 ns (~23x wall)
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Formula (``starWithBackEdges(V)``): before = ``V*(V+1)/2 - 1``; after = ``V - 1``
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Complexity Proof
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----------------
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Let V = number of nodes visited by Tarjan SCC. The defective code calls ``stack.contains(n)``
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once per node popped from the stack; the stack can hold up to V elements at that point, so each
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call costs O(V). With V pops total the cost is O(V²). The patched code tests a boolean field on
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the node object — O(1) per test, O(V) total. QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0001.md``
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* Patch: ``defects/javac/patch/``
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* Tests: ``tests/unit/``, ``tests/integration/InferenceGraphScalingTest.java``
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javac-0002a
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~~~~~~~~~~~
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**File:** ``src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Infer.java:1850``
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**Pattern:**
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.. code-block:: java
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// Type inference graph — node lookup by identity
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List<Node> nodes = new ArrayList<>();
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// ...
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Node findNode(InferenceVar iv) {
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for (Node n : nodes) { // O(N) linear scan
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if (n.data.contains(iv)) return n;
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}
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return null;
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}
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**Why this is O(n):** ``ArrayList`` lookup by value; called O(N) times during inference graph
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construction, giving O(N²) total.
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**Complexity:** ``O(N²)`` where N = number of type variables in the inference graph
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**Patch:**
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.. code-block:: java
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Map<InferenceVar, Node> nodeMap = new HashMap<>();
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Node findNode(InferenceVar iv) {
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return nodeMap.get(iv); // O(1)
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}
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**Data structure change:** ``List<Node> nodes`` + linear scan → ``HashMap<InferenceVar, Node> nodeMap``
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**Status:** Patched (source only; API drift vs JDK 21 blocks recompilation against installed JDK)
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Benchmark Results
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-----------------
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Formula (``queryAll(N)``): before = ``N*(N+1)/2``; after = ``N``
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.. list-table::
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:header-rows: 1
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* - N (type vars)
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- Before (ops)
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- After (ops)
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- Ratio
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* - 100
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- 5,050
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- 100
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- 50x
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* - 500
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- 125,250
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- 500
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- 250x
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Complexity Proof
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----------------
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Let N = number of type-variable nodes in the inference graph. ``findNode`` is called once per
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node during graph construction; each call scans a list of up to N elements: O(N²) total. The
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HashMap patch reduces each lookup to O(1) amortized: O(N) total. QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0002a.md``
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* Patch: ``defects/javac/patch/``
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* Tests: ``tests/unit/``
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javac-0002b
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~~~~~~~~~~~
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**File:** ``src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Infer.java:1747``
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**Pattern:**
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.. code-block:: java
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// Type inference — uncached closure DFS
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List<Node> closure(Node n) {
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List<Node> result = new ArrayList<>();
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result.add(n);
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for (Node dep : n.deps) {
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for (Node c : closure(dep)) { // recomputes full closure on every call
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if (!result.contains(c)) result.add(c);
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}
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}
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return result;
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}
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**Why this is O(n):** Closure is recomputed from scratch on every call; contains() is O(V) inside
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the recursion.
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**Complexity:** ``O(K·V)`` where K = number of closure queries, V = graph size
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**Patch:**
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.. code-block:: java
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// Cache closure results; use Set for membership
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Map<Node, Set<Node>> closureCache = new HashMap<>();
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Set<Node> closure(Node n) {
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if (closureCache.containsKey(n)) return closureCache.get(n);
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Set<Node> result = new LinkedHashSet<>();
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result.add(n);
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for (Node dep : n.deps) result.addAll(closure(dep));
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closureCache.put(n, result);
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return result;
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}
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**Data structure change:** ``List<Node>`` uncached → ``LinkedHashSet<Node>`` with HashMap cache
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**Status:** Patched (source only; API drift vs JDK 21 blocks recompilation)
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Benchmark Results
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-----------------
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Formula (``closureFixed K calls on chain(V)``): before = ``K*V``; after = ``V + (K-1)``
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Complexity Proof
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----------------
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Let V = graph nodes, K = closure calls. Without caching, each of K calls traverses up to V nodes:
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O(K·V). With memoization, each node is visited once across all K calls: O(V) total traversal
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plus O(K) cache hits = O(V + K). QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0002b.md``
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* Patch: ``defects/javac/patch/``
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* Tests: ``tests/unit/``
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javac-0003
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~~~~~~~~~~
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**File:** ``java.base`` module — ``ModuleHashesBuilder`` (not in sparse checkout)
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**Pattern:**
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.. code-block:: java
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// Module dependency traversal — Deque membership test
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Deque<String> visited = new ArrayDeque<>();
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// ...
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if (!visited.contains(moduleName)) { // O(V) linear scan
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visited.push(moduleName);
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...
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}
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**Why this is O(n):** ``ArrayDeque.contains()`` walks all elements; called once per module
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dependency edge.
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**Complexity:** ``O(V*(V-1)/2)`` where V = number of modules in the dependency graph
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**Patch:**
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.. code-block:: java
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Set<String> visited = new HashSet<>();
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if (visited.add(moduleName)) { // O(1) — add returns false if already present
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...
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}
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**Data structure change:** ``Deque<String>`` + ``contains()`` → ``HashSet<String>`` + ``add()``
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**Status:** Unpatched (file not in sparse checkout; requires full ``java.base`` module clone)
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Benchmark Results
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-----------------
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.. TODO: benchmark pending patch
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Formula (``linearChain(V)``): before = ``V*(V-1)/2``; after = ``V``
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Complexity Proof
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----------------
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Let V = number of distinct modules. The defective code calls ``Deque.contains()`` once per
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module visit; at step i the deque holds i elements: total cost = 0 + 1 + ... + (V-1) = O(V²).
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The HashSet patch costs O(1) per insert/test: O(V) total. QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0003.md``
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javac-0004
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~~~~~~~~~~
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**File:** ``src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Dependencies.java:197``
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**Pattern:**
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.. code-block:: java
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// Annotation processing dependency tracking
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List<ClassSymbol> deps = new ArrayList<>();
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void addDependency(ClassSymbol sym) {
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if (!deps.contains(sym)) { // O(M) linear scan
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deps.add(sym);
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}
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}
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**Why this is O(n):** ``ArrayList.contains()`` + ``ArrayList.add()`` pattern; called M times
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gives O(M²) total.
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**Complexity:** ``O(M²)`` where M = number of unique annotation processing dependencies
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**Patch:**
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.. code-block:: java
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LinkedHashSet<ClassSymbol> deps = new LinkedHashSet<>();
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void addDependency(ClassSymbol sym) {
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deps.add(sym); // O(1) — set.add() is idempotent; no separate contains() needed
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}
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**Data structure change:** ``List<ClassSymbol>`` + ``contains+add`` → ``LinkedHashSet<ClassSymbol>``
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**Status:** Patched
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Benchmark Results
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-----------------
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Formula (``addUnique(M)``): before = ``M*(M-1)/2``; after = ``M``
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.. list-table::
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:header-rows: 1
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* - M (dependencies)
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- Before (ops)
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- After (ops)
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- Ratio
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* - 100
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- 4,950
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- 100
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- 49x
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* - 500
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- 124,750
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- 500
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- 249x
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Complexity Proof
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----------------
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Let M = number of unique dependencies added. Each ``addDependency`` call first scans the list
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(cost = current list length). Total cost = 0 + 1 + ... + (M-1) = M*(M-1)/2 = O(M²). The
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LinkedHashSet patch performs one O(1) ``add()`` per call: O(M) total. QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0004.md``
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* Patch: ``defects/javac/patch/``
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* Tests: ``tests/unit/``, ``tests/integration/``
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javac-0005
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~~~~~~~~~~
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**File:** ``src/jdk.compiler/share/classes/com/sun/tools/javac/comp/InferenceContext.java:506``
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**Pattern:**
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.. code-block:: java
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// Type variable bounds equivalence check
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boolean isEquiv(List<Type> boundsA, List<Type> boundsB) {
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return boundsA.containsAll(boundsB) && boundsB.containsAll(boundsA);
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}
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// called inside type inference loop — O(B²) per call
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**Why this is O(n):** ``List.containsAll()`` is O(|A|×|B|); called on forward and reversed
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bounds lists of length B.
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**Complexity:** ``O(B²)`` where B = number of type bounds being compared
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**Patch:**
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.. code-block:: java
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boolean isEquiv(List<Type> boundsA, List<Type> boundsB) {
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return new HashSet<>(boundsA).equals(new HashSet<>(boundsB));
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}
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**Data structure change:** ``List.containsAll()`` × 2 → ``HashSet.equals()``
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**Status:** Patched
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Benchmark Results
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-----------------
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Formula (``isEquiv forward vs reversed(B)``): before = ``B*(B+1)``; after = ``B``
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.. list-table::
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:header-rows: 1
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* - B (type bounds)
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- Before (ops)
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- After (ops)
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- Ratio
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* - 50
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- 2,550
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- 50
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- 51x
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* - 200
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- 40,200
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- 200
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- 201x
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Complexity Proof
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----------------
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Let B = number of type bounds. ``List.containsAll(other)`` scans ``other`` for each element of
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``self``: O(B²). Called twice (forward and reversed) gives O(2B²) = O(B²). ``HashSet.equals()``
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hashes all elements of both sets: O(B). QED.
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References
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----------
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* Defect ticket: ``tools/tickets/defects/javac-0005.md``
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* Patch: ``defects/javac/patch/``
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* Tests: ``tests/unit/``, ``tests/integration/``
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