From 94e6d2677bd3748b344aa5abccfc7284dbea8be0 Mon Sep 17 00:00:00 2001
From: Lang Hames <lhames@gmail.com>
Date: Tue, 19 Jul 2022 17:19:58 -0700
Subject: [PATCH] [ORC] Fix serialization / deserialization of
 default-constructed StringRef.

Avoids accessing the data field on zero-length strings. This is the StringRef
counterpart to the ArrayRef<char> fix in 67220c2ad72e3.

rdar://97285294
---
 .../Orc/Shared/SimplePackedSerialization.h          |  4 +++-
 .../Orc/SimplePackedSerializationTest.cpp           | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/ExecutionEngine/Orc/Shared/SimplePackedSerialization.h b/llvm/include/llvm/ExecutionEngine/Orc/Shared/SimplePackedSerialization.h
index 794c07b..c388259 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/Shared/SimplePackedSerialization.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/Shared/SimplePackedSerialization.h
@@ -479,6 +479,8 @@ public:
   static bool serialize(SPSOutputBuffer &OB, StringRef S) {
     if (!SPSArgList<uint64_t>::serialize(OB, static_cast<uint64_t>(S.size())))
       return false;
+    if (S.empty()) // Empty StringRef may have null data, so bail out early.
+      return true;
     return OB.write(S.data(), S.size());
   }
 
@@ -490,7 +492,7 @@ public:
     Data = IB.data();
     if (!IB.skip(Size))
       return false;
-    S = StringRef(Data, Size);
+    S = StringRef(Size ? Data : nullptr, Size);
     return true;
   }
 };
diff --git a/llvm/unittests/ExecutionEngine/Orc/SimplePackedSerializationTest.cpp b/llvm/unittests/ExecutionEngine/Orc/SimplePackedSerializationTest.cpp
index f5319e3..ee73614 100644
--- a/llvm/unittests/ExecutionEngine/Orc/SimplePackedSerializationTest.cpp
+++ b/llvm/unittests/ExecutionEngine/Orc/SimplePackedSerializationTest.cpp
@@ -208,3 +208,24 @@ TEST(SimplePackedSerializationTest, ArrayRefEmpty) {
   EXPECT_EQ(AIn.data(), nullptr);
   EXPECT_EQ(AIn.size(), 0U);
 }
+
+TEST(SimplePackedSerializationTest, StringRefEmpty) {
+  // Make sure that empty StringRefs serialize and deserialize as expected.
+  // Empty StringRefs should not succeed even when the data field is null, and
+  // should deserialize to a default-constructed StringRef, not a pointer into
+  // the stream.
+  constexpr unsigned BufferSize = sizeof(uint64_t);
+  char Buffer[BufferSize];
+  memset(Buffer, 0, BufferSize);
+
+  StringRef SROut;
+  SPSOutputBuffer OB(Buffer, BufferSize);
+  EXPECT_TRUE(SPSArgList<SPSSequence<char>>::serialize(OB, SROut));
+
+  StringRef SRIn;
+  SPSInputBuffer IB(Buffer, BufferSize);
+  EXPECT_TRUE(SPSArgList<SPSSequence<char>>::deserialize(IB, SRIn));
+
+  EXPECT_EQ(SRIn.data(), nullptr);
+  EXPECT_EQ(SRIn.size(), 0U);
+}
-- 
2.7.4