Merge pull request #58913 from mikeash/internal-new-delete-5.7

[5.7][Runtime] Define our own hidden global new/delete on Darwin.

Author: mikeash

stdlib/public/runtime/Heap.cpp

@@ -119,7 +119,7 @@ void *swift::swift_slowAlloc(size_t size, size_t alignMask) {
 // i.e. 0 < alignment <= _minAllocationAlignment:
 //   The runtime may use either `free` or AlignedFree as long as it is
 //   consistent with allocation with the same alignment.
-void swift::swift_slowDealloc(void *ptr, size_t bytes, size_t alignMask) {
+static void swift_slowDeallocImpl(void *ptr, size_t alignMask) {
   if (alignMask <= MALLOC_ALIGN_MASK) {
 #if defined(__APPLE__) && SWIFT_STDLIB_HAS_DARWIN_LIBMALLOC
     malloc_zone_free(DEFAULT_ZONE(), ptr);
@@ -130,3 +130,34 @@ void swift::swift_slowDealloc(void *ptr, size_t bytes, size_t alignMask) {
     AlignedFree(ptr);
   }
 }
+
+void swift::swift_slowDealloc(void *ptr, size_t bytes, size_t alignMask) {
+  swift_slowDeallocImpl(ptr, alignMask);
+}
+
+#if defined(__APPLE__) && defined(__MACH__) && SWIFT_STDLIB_HAS_DARWIN_LIBMALLOC
+// On Darwin, define our own, hidden operator new/delete implementations. We
+// don't want to pick up any overrides that come from other code, but we also
+// don't want to expose our overrides to any other code. We can't do this
+// directly in C++, as the compiler has an implicit prototype with default
+// visibility. However, if we implement them as C functions using the C++
+// mangled names, the compiler accepts them without complaint, and the linker
+// still links all internal uses with these overrides.
+
+__attribute__((visibility(("hidden")))) extern "C" void *_Znwm(size_t size) {
+  return swift_slowAlloc(size, MALLOC_ALIGN_MASK);
+}
+
+__attribute__((visibility(("hidden")))) extern "C" void _ZdlPv(void *ptr) {
+  swift_slowDeallocImpl(ptr, MALLOC_ALIGN_MASK);
+}
+
+__attribute__((visibility(("hidden")))) extern "C" void *_Znam(size_t size) {
+  return swift_slowAlloc(size, MALLOC_ALIGN_MASK);
+}
+
+__attribute__((visibility(("hidden")))) extern "C" void _ZdaPv(void *ptr) {
+  swift_slowDeallocImpl(ptr, MALLOC_ALIGN_MASK);
+}
+
+#endif