Fix MismatchedAlignedDelete fuzz test by bypassing matched cases.

PiperOrigin-RevId: 875333740
Change-Id: I8ce9259b3ac8524baa9f763487bf7f9390557583

Author: TCMalloc Team

tcmalloc/testing/memory_errors_fuzz.cc

@@ -32,7 +32,9 @@
 #include "tcmalloc/internal/memory_tag.h"
 #include "tcmalloc/internal_malloc_extension.h"
 #include "tcmalloc/malloc_extension.h"
+#include "tcmalloc/static_vars.h"
 #include "tcmalloc/tcmalloc.h"
+#include "tcmalloc/tcmalloc_policy.h"
 #include "tcmalloc/testing/testutil.h"
 
 namespace tcmalloc::tcmalloc_internal {
@@ -167,10 +169,51 @@ void MismatchedAlignedDelete(
   } else {
     ptr = TCMallocInternalNewNothrow(size, std::nothrow);
   }
+
   if (ptr == nullptr) {
     return;
   }
 
+  // Alignment mismatches that result in different size classes
+  // will cause catatrophic failures. Detection of such error
+  // conditions is tested, but we need to by-pass inputs that are
+  // valid.
+  //
+  // Here are the normal conditions to be bypassed:
+  // 1. Alignment is specified neither in allocation nor deallocation
+  //     -- always ok
+  // 2. Alignment is specified in allocation, but not deallocation:
+  //     -- ok when the size of the corresponding size class's
+  //     -- natural alignment >= requested alignment (then no size class
+  //     -- adjustment is needed in deallocation)
+  // 3. Alignment is not specified in allocation, but in deallocation
+  //     -- same as above
+  // 4. When both are specified:
+  //     -- ok when the alignment are equal or
+  //     -- both are greater than kPageSize or
+  //     -- size_class adjustments are needed in neither cases.
+
+  auto [is_small_a, size_class_a] =
+      allocated_alignment.has_value()
+          ? tc_globals.sizemap().GetSizeClass(
+                CppPolicy().Nothrow().AlignAs(*allocated_alignment), size)
+          : tc_globals.sizemap().GetSizeClass(CppPolicy().Nothrow(), size);
+
+  auto [is_small_d, size_class_d] =
+      deallocated_alignment.has_value()
+          ? tc_globals.sizemap().GetSizeClass(
+                CppPolicy().Nothrow().AlignAs(*deallocated_alignment), size)
+          : tc_globals.sizemap().GetSizeClass(CppPolicy().Nothrow(), size);
+
+  if (is_small_a && is_small_d && size_class_a == size_class_d) {
+    if (deallocated_alignment.has_value()) {
+      TCMallocInternalDeleteSizedAligned(ptr, size, *deallocated_alignment);
+    } else {
+      TCMallocInternalDeleteSized(ptr, size);
+    }
+    return;
+  }
+
   LongJmpScope scope;
   if (setjmp(scope.buf_)) {
     return;
@@ -181,7 +224,11 @@ void MismatchedAlignedDelete(
   } else {
     TCMallocInternalDeleteSized(ptr, size);
   }
-  EXPECT_EQ(allocated_alignment, deallocated_alignment);
+
+  // The alignment error detecion is only available with debug build
+#ifndef NDEBUG
+  EXPECT_TRUE(!is_small_a && !is_small_d);
+#endif
 }
 
 FUZZ_TEST(MemoryErrorsFuzzTest, MismatchedAlignedDelete)