diff --git a/lldb/include/lldb/Core/DataFileCache.h b/lldb/include/lldb/Core/DataFileCache.h
--- a/lldb/include/lldb/Core/DataFileCache.h
+++ b/lldb/include/lldb/Core/DataFileCache.h
@@ -119,22 +119,22 @@
     m_obj_mod_time = llvm::None;
   }
 
-  /// Return true if any of the signature member variables have valid values.
-  bool IsValid() const {
-    return m_uuid.hasValue() || m_mod_time.hasValue() ||
-           m_obj_mod_time.hasValue();
-  }
+  /// Return true only if the CacheSignature is valid.
+  ///
+  /// Cache signatures are considered valid only if there is a UUID in the file
+  /// that can uniquely identify the file. Some build systems play with
+  /// modification times of file so we can not trust them without using valid
+  /// unique idenifier like the UUID being valid.
+  bool IsValid() const { return m_uuid.hasValue(); }
 
   /// Check if two signatures are the same.
-  bool operator!=(const CacheSignature &rhs) {
-    if (m_uuid != rhs.m_uuid)
-      return true;
-    if (m_mod_time != rhs.m_mod_time)
-      return true;
-    if (m_obj_mod_time != rhs.m_obj_mod_time)
-      return true;
-    return false;
+  bool operator==(const CacheSignature &rhs) const {
+    return m_uuid == rhs.m_uuid && m_mod_time == rhs.m_mod_time &&
+           m_obj_mod_time == rhs.m_obj_mod_time;
   }
+
+  /// Check if two signatures differ.
+  bool operator!=(const CacheSignature &rhs) const { return !(*this == rhs); }
   /// Encode this object into a data encoder object.
   ///
   /// This allows this object to be serialized to disk. The CacheSignature
@@ -149,7 +149,7 @@
   ///   True if a signature was encoded, and false if there were no member
   ///   variables that had value. False indicates this data should not be
   ///   cached to disk because we were unable to encode a valid signature.
-  bool Encode(DataEncoder &encoder);
+  bool Encode(DataEncoder &encoder) const;
 
   /// Decode a serialized version of this object from data.
   ///
diff --git a/lldb/source/Core/DataFileCache.cpp b/lldb/source/Core/DataFileCache.cpp
--- a/lldb/source/Core/DataFileCache.cpp
+++ b/lldb/source/Core/DataFileCache.cpp
@@ -199,7 +199,7 @@
   eSignatureEnd = 255u,
 };
 
-bool CacheSignature::Encode(DataEncoder &encoder) {
+bool CacheSignature::Encode(DataEncoder &encoder) const {
   if (!IsValid())
     return false; // Invalid signature, return false!
 
@@ -240,10 +240,14 @@
     case eSignatureObjectModTime: {
       uint32_t mod_time = data.GetU32(offset_ptr);
       if (mod_time > 0)
-        m_mod_time = mod_time;
+        m_obj_mod_time = mod_time;
     } break;
     case eSignatureEnd:
-      return true;
+      // The definition of is valid changed to only be valid if the UUID is
+      // valid so make sure that if we attempt to decode an old cache file
+      // that we will fail to decode the cache file if the signature isn't
+      // considered valid.
+      return IsValid();
     default:
       break;
     }
diff --git a/lldb/test/API/functionalities/module_cache/bsd/TestModuleCacheBSD.py b/lldb/test/API/functionalities/module_cache/bsd/TestModuleCacheBSD.py
--- a/lldb/test/API/functionalities/module_cache/bsd/TestModuleCacheBSD.py
+++ b/lldb/test/API/functionalities/module_cache/bsd/TestModuleCacheBSD.py
@@ -41,6 +41,25 @@
     @skipUnlessDarwin
     def test(self):
         """
+            This test has been modified to make sure .o files that don't have
+            UUIDs are not cached after discovering build systems that play with
+            modification times of .o files that the modification times are not
+            unique enough to ensure the .o file within the .a file are the right
+            files as this was causing older cache files to be accepted for new
+            updated .o files.
+
+            ELF .o files do calculate a UUID from the contents of the file,
+            which is expensive, but no one loads .o files into a debug sessions
+            when using ELF files. Mach-o .o files do not have UUID values and do
+            no calculate one as they _are_ used during debug sessions when no
+            dSYM file is generated. If we can find a way to uniquely and cheaply
+            create UUID values for mach-o .o files in the future, this test will
+            be updated to test this functionality. This test will now make sure
+            there are no cache entries for any .o files in BSD archives.
+
+            The old test case description is below in case we enable caching for
+            .o files again:
+
             Test module cache functionality for bsd archive object files.
 
             This will test that if we enable the module cache, we have a
@@ -76,10 +95,20 @@
         main_module.GetNumSymbols()
         a_o_cache_files = self.get_module_cache_files("libfoo.a(a.o)")
         b_o_cache_files = self.get_module_cache_files("libfoo.a(b.o)")
+
+
         # We expect the directory for a.o to have two cache directories:
         # - 1 for the a.o with a earlier mod time
         # - 1 for the a.o that was renamed from c.o that should be 2 seconds older
-        self.assertEqual(len(a_o_cache_files), 2,
-                "make sure there are two files in the module cache directory (%s) for libfoo.a(a.o)" % (self.cache_dir))
-        self.assertEqual(len(b_o_cache_files), 1,
-                "make sure there are two files in the module cache directory (%s) for libfoo.a(b.o)" % (self.cache_dir))
+        # self.assertEqual(len(a_o_cache_files), 2,
+        #         "make sure there are two files in the module cache directory (%s) for libfoo.a(a.o)" % (self.cache_dir))
+        # self.assertEqual(len(b_o_cache_files), 1,
+        #         "make sure there are two files in the module cache directory (%s) for libfoo.a(b.o)" % (self.cache_dir))
+
+        # We are no longer caching .o files in the lldb index cache. If we ever
+        # re-enable this functionality, we can uncomment out the above lines of
+        # code.
+        self.assertEqual(len(a_o_cache_files), 0,
+                "make sure there are no files in the module cache directory (%s) for libfoo.a(a.o)" % (self.cache_dir))
+        self.assertEqual(len(b_o_cache_files), 0,
+                "make sure there are no files in the module cache directory (%s) for libfoo.a(b.o)" % (self.cache_dir))
diff --git a/lldb/unittests/SymbolFile/DWARF/DWARFIndexCachingTest.cpp b/lldb/unittests/SymbolFile/DWARF/DWARFIndexCachingTest.cpp
--- a/lldb/unittests/SymbolFile/DWARF/DWARFIndexCachingTest.cpp
+++ b/lldb/unittests/SymbolFile/DWARF/DWARFIndexCachingTest.cpp
@@ -196,3 +196,75 @@
       DIERef(llvm::None, DIERef::Section::DebugInfo, ++die_offset));
   EncodeDecode(set);
 }
+
+static void EncodeDecode(const CacheSignature &object, ByteOrder byte_order,
+                         bool encode_result) {
+  const uint8_t addr_size = 8;
+  DataEncoder encoder(byte_order, addr_size);
+  EXPECT_EQ(encode_result, object.Encode(encoder));
+  if (!encode_result)
+    return;
+  llvm::ArrayRef<uint8_t> bytes = encoder.GetData();
+  DataExtractor data(bytes.data(), bytes.size(), byte_order, addr_size);
+  offset_t data_offset = 0;
+  CacheSignature decoded_object;
+  EXPECT_TRUE(decoded_object.Decode(data, &data_offset));
+  EXPECT_EQ(object, decoded_object);
+}
+
+static void EncodeDecode(const CacheSignature &object, bool encode_result) {
+  EncodeDecode(object, eByteOrderLittle, encode_result);
+  EncodeDecode(object, eByteOrderBig, encode_result);
+}
+
+TEST(DWARFIndexCachingTest, CacheSignatureTests) {
+  CacheSignature sig;
+  // A cache signature is only considered valid if it has a UUID.
+  sig.m_mod_time = 0x12345678;
+  EXPECT_FALSE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/false);
+  sig.Clear();
+
+  sig.m_obj_mod_time = 0x12345678;
+  EXPECT_FALSE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/false);
+  sig.Clear();
+
+  sig.m_uuid = UUID::fromData("@\x00\x11\x22\x33\x44\x55\x66\x77", 8);
+  EXPECT_TRUE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/true);
+  sig.m_mod_time = 0x12345678;
+  EXPECT_TRUE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/true);
+  sig.m_obj_mod_time = 0x456789ab;
+  EXPECT_TRUE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/true);
+  sig.m_mod_time = llvm::None;
+  EXPECT_TRUE(sig.IsValid());
+  EncodeDecode(sig, /*encode_result=*/true);
+
+  // Recent changes do not allow cache signatures with only a modification time
+  // or object modification time, so make sure if we try to decode such a cache
+  // file that we fail. This verifies that if we try to load an previously
+  // valid cache file where the signature is insufficient, that we will fail to
+  // decode and load these cache files.
+  DataEncoder encoder(eByteOrderLittle, /*addr_size=*/8);
+  encoder.AppendU8(2); // eSignatureModTime
+  encoder.AppendU32(0x12345678);
+  encoder.AppendU8(255); // eSignatureEnd
+
+  llvm::ArrayRef<uint8_t> bytes = encoder.GetData();
+  DataExtractor data(bytes.data(), bytes.size(), eByteOrderLittle,
+                     /*addr_size=*/8);
+  offset_t data_offset = 0;
+
+  // Make sure we fail to decode a CacheSignature with only a mod time
+  EXPECT_FALSE(sig.Decode(data, &data_offset));
+
+  // Change the signature data to contain only a eSignatureObjectModTime and
+  // make sure decoding fails as well.
+  encoder.PutU8(/*offset=*/0, 3); // eSignatureObjectModTime
+  data_offset = 0;
+  EXPECT_FALSE(sig.Decode(data, &data_offset));
+
+}