[scudo] Add static vector functionality. (#98986)

Summary:
The scudo vector implementation maintains static local data before 
switching to dynamically allocated data as the array size grows.
Users of the vector must now specify the size of the static local data 
through the vector template (the default size has been removed). 
If 0 is specified for the size of the static local data, an assertion
will
be triggered.

Test Plan: 

Reviewers: 

Subscribers: 

Tasks: 

Tags: 


Differential Revision: https://phabricator.intern.facebook.com/D60250929

Author: JoshuaMBa

compiler-rt/lib/scudo/standalone/string_utils.h

@@ -40,7 +40,7 @@ class ScopedString {
   void appendString(int Width, int MaxChars, const char *S);
   void appendPointer(u64 ptr_value);
 
-  Vector<char> String;
+  Vector<char, 256> String;
 };
 
 void Printf(const char *Format, ...) FORMAT(1, 2);

compiler-rt/lib/scudo/standalone/tests/vector_test.cpp

@@ -11,7 +11,7 @@
 #include "vector.h"
 
 TEST(ScudoVectorTest, Basic) {
-  scudo::Vector<int> V;
+  scudo::Vector<int, 64U> V;
   EXPECT_EQ(V.size(), 0U);
   V.push_back(42);
   EXPECT_EQ(V.size(), 1U);
@@ -23,7 +23,7 @@ TEST(ScudoVectorTest, Basic) {
 }
 
 TEST(ScudoVectorTest, Stride) {
-  scudo::Vector<scudo::uptr> V;
+  scudo::Vector<scudo::uptr, 32U> V;
   for (scudo::uptr I = 0; I < 1000; I++) {
     V.push_back(I);
     EXPECT_EQ(V.size(), I + 1U);
@@ -34,7 +34,7 @@ TEST(ScudoVectorTest, Stride) {
 }
 
 TEST(ScudoVectorTest, ResizeReduction) {
-  scudo::Vector<int> V;
+  scudo::Vector<int, 64U> V;
   V.push_back(0);
   V.push_back(0);
   EXPECT_EQ(V.size(), 2U);
@@ -48,7 +48,7 @@ TEST(ScudoVectorTest, ResizeReduction) {
 
 // Verify that if the reallocate fails, nothing new is added.
 TEST(ScudoVectorTest, ReallocateFails) {
-  scudo::Vector<char> V;
+  scudo::Vector<char, 256U> V;
   scudo::uptr capacity = V.capacity();
 
   // Get the current address space size.

compiler-rt/lib/scudo/standalone/vector.h

@@ -21,7 +21,7 @@ namespace scudo {
 // implementation supports only POD types.
 //
 // NOTE: This class is not meant to be used directly, use Vector<T> instead.
-template <typename T> class VectorNoCtor {
+template <typename T, size_t StaticNumEntries> class VectorNoCtor {
 public:
   T &operator[](uptr I) {
     DCHECK_LT(I, Size);
@@ -116,18 +116,21 @@ template <typename T> class VectorNoCtor {
   uptr CapacityBytes = 0;
   uptr Size = 0;
 
-  T LocalData[256 / sizeof(T)] = {};
+  T LocalData[StaticNumEntries] = {};
   MemMapT ExternalBuffer;
 };
 
-template <typename T> class Vector : public VectorNoCtor<T> {
+template <typename T, size_t StaticNumEntries>
+class Vector : public VectorNoCtor<T, StaticNumEntries> {
 public:
-  constexpr Vector() { VectorNoCtor<T>::init(); }
+  static_assert(StaticNumEntries > 0U,
+                "Vector must have a non-zero number of static entries.");
+  constexpr Vector() { VectorNoCtor<T, StaticNumEntries>::init(); }
   explicit Vector(uptr Count) {
-    VectorNoCtor<T>::init(Count);
+    VectorNoCtor<T, StaticNumEntries>::init(Count);
     this->resize(Count);
   }
-  ~Vector() { VectorNoCtor<T>::destroy(); }
+  ~Vector() { VectorNoCtor<T, StaticNumEntries>::destroy(); }
   // Disallow copies and moves.
   Vector(const Vector &) = delete;
   Vector &operator=(const Vector &) = delete;