Merge pull request #37506 from mikeash/remotemirror-malloc-null-checks-5.5

[5.5][RemoteMirror] Add NULL checks to Remote Mirror malloc calls.

Author: mikeash

include/swift/Remote/MemoryReader.h

@@ -100,6 +100,8 @@ class MemoryReader {
   virtual ReadBytesResult
   readBytes(RemoteAddress address, uint64_t size) {
     auto *Buf = malloc(size);
+    if (!Buf)
+      return ReadBytesResult{};
     ReadBytesResult Result(Buf, [](const void *ptr) {
       free(const_cast<void *>(ptr));
     });

include/swift/Remote/MetadataReader.h

@@ -1802,6 +1802,9 @@ class MetadataReader {
   MetadataRef _readMetadata(StoredPointer address, size_t sizeAfter) {
     auto size = sizeAfter;
     uint8_t *buffer = (uint8_t *) malloc(size);
+    if (!buffer)
+      return nullptr;
+
     if (!Reader->readBytes(RemoteAddress(address), buffer, size)) {
       free(buffer);
       return nullptr;
@@ -2522,6 +2525,8 @@ class MetadataReader {
   std::string readObjCProtocolName(StoredPointer Address) {
     auto Size = sizeof(TargetObjCProtocolPrefix<Runtime>);
     auto Buffer = (uint8_t *)malloc(Size);
+    if (!Buffer)
+      return std::string();
     SWIFT_DEFER {
       free(Buffer);
     };