scudo: Test realloc on increasing size buffers.

[pcc]

Summary

While developing a change to the allocator I ended up breaking
realloc on secondary allocations with increasing sizes. That didn't
cause any of the unit tests to fail, which indicated that we're
missing some test coverage here. Add a unit test for that case.

[hctim]

It's funny you mention this, I think this is one of the problems that I saw in https://reviews.llvm.org/D102543#change-dE7v8cbuK8l4 (but there are other bugs also in realloc.cpp that need to be addressed as well). Is the fix already merged into the tree or yet to come?

[cryptoad]

Thank you Peter!

[pcc]

In D102716#2767104, @hctim wrote:

It's funny you mention this, I think this is one of the problems that I saw in https://reviews.llvm.org/D102543#change-dE7v8cbuK8l4 (but there are other bugs also in realloc.cpp that need to be addressed as well). Is the fix already merged into the tree or yet to come?

I think that must be a different bug. The test that I'm adding here passes at head.

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

for (scudo::uptr I = 0; I < 1024U && !Found; I++) {
     if (Allocator->getHeaderTaggedPointer(P) ==
         Allocator->getHeaderTaggedPointer(NeedleP))
       Found = true;
     Allocator->deallocate(P, Origin);
   }
   EXPECT_TRUE(Found);
 }
 
-SCUDO_TYPED_TEST(ScudoCombinedTest, ReallocateLarge) {
+SCUDO_TYPED_TEST(ScudoCombinedTest, ReallocateLargeIncreasing) {
+  auto *Allocator = this->Allocator.get();
+
+  // Reallocate a chunk all the way up to a secondary allocation, verifying that
+  // we preserve the data in the process.
+  scudo::uptr Size = 16;
+  void *P = Allocator->allocate(Size, Origin);
+  const char Marker = 0xab;
+  memset(P, Marker, Size);
+  while (Size < TypeParam::Primary::SizeClassMap::MaxSize * 4) {
+    void *NewP = Allocator->reallocate(P, Size * 2);
+    EXPECT_NE(NewP, nullptr);
+    for (scudo::uptr J = 0; J < Size; J++)
+      EXPECT_EQ((reinterpret_cast<char *>(NewP))[J], Marker);
+    memset(reinterpret_cast<char *>(NewP) + Size, Marker, Size);
+    Size *= 2U;
+    P = NewP;
+  }
+  Allocator->deallocate(P, Origin);
+}
+
+SCUDO_TYPED_TEST(ScudoCombinedTest, ReallocateLargeDecreasing) {
   auto *Allocator = this->Allocator.get();
 
   // Reallocate a large chunk all the way down to a byte, verifying that we
   // preserve the data in the process.
   scudo::uptr Size = TypeParam::Primary::SizeClassMap::MaxSize * 2;
   const scudo::uptr DataSize = 2048U;
   void *P = Allocator->allocate(Size, Origin);
   const char Marker = 0xab;