Aix: Avoid using Malloc::GetUsableSize

Change-Id: I99b4c5d9ea6183acf629f5f76ebb0f84c88e7b20
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3855198
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Milad Farazmand <mfarazma@redhat.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82715}

src/base/platform/platform-posix.cc

@@ -1269,7 +1269,11 @@ Stack::StackSlot Stack::GetCurrentStackPosition() {
 size_t Malloc::GetUsableSize(void* ptr) {
 #if defined(V8_OS_DARWIN)
   return malloc_size(ptr);
-#else   // defined(V8_OS_DARWIN)
+#elif defined(V8_OS_AIX)
+  // malloc_usable_size is not available, and there is no equivalent
+  UNIMPLEMENTED();
+  return 0;
+#else
   return malloc_usable_size(ptr);
 #endif  // !defined(V8_OS_DARWIN)
 }

src/base/platform/platform.h

@@ -683,6 +683,10 @@ class V8_BASE_EXPORT Malloc final {
   V8_NODISCARD static AllocationResult<T*> AllocateAtLeast(std::size_t n) {
     const size_t min_wanted_size = n * sizeof(T);
     auto* memory = static_cast<T*>(malloc(min_wanted_size));
+#if defined(V8_OS_AIX)
+    // GetUsableSize() is not implemented on Aix
+    return {memory, min_wanted_size};
+#else
     const size_t usable_size = v8::base::Malloc::GetUsableSize(memory);
 #if V8_USE_UNDEFINED_BEHAVIOR_SANITIZER
     // UBSan (specifically, -fsanitize=bounds) assumes that any access outside
@@ -695,6 +699,7 @@ class V8_BASE_EXPORT Malloc final {
     }
 #endif  // V8_USE_UNDEFINED_BEHAVIOR_SANITIZER
     return {memory, usable_size};
+#endif  // defined(V8_OS_AIX)
   }
 };