diff --git a/llvm/lib/DebugInfo/CodeView/Formatters.cpp b/llvm/lib/DebugInfo/CodeView/Formatters.cpp
--- a/llvm/lib/DebugInfo/CodeView/Formatters.cpp
+++ b/llvm/lib/DebugInfo/CodeView/Formatters.cpp
@@ -23,6 +23,17 @@
 GuidAdapter::GuidAdapter(ArrayRef<uint8_t> Guid)
     : FormatAdapter(std::move(Guid)) {}
 
+// From https://docs.microsoft.com/en-us/windows/win32/msi/guid documentation:
+// The GUID data type is a text string representing a Class identifier (ID).
+// All GUIDs must be authored in uppercase.
+// The valid format for a GUID is {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} where
+// X is a hex digit (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F).
+//
+// The individual string components must be padded to comply with the specific
+// lengths of {8-4-4-4-12} characters.
+// The llvm-yaml2obj tool checks that a GUID follow that format:
+// - the total length to be 38 (including the curly braces.
+// - there is a dash at the positions: 8, 13, 18 and 23.
 void GuidAdapter::format(raw_ostream &Stream, StringRef Style) {
   assert(Item.size() == 16 && "Expected 16-byte GUID");
   struct MSGuid {
@@ -33,11 +44,11 @@
   };
   const MSGuid *G = reinterpret_cast<const MSGuid *>(Item.data());
   Stream
-      << '{' << format_hex_no_prefix(G->Data1, sizeof(G->Data1), /*Upper=*/true)
-      << '-' << format_hex_no_prefix(G->Data2, sizeof(G->Data2), /*Upper=*/true)
-      << '-' << format_hex_no_prefix(G->Data3, sizeof(G->Data3), /*Upper=*/true)
-      << '-' << format_hex_no_prefix(G->Data4 >> 48, 2, /*Upper=*/true) << '-'
-      << format_hex_no_prefix(G->Data4 & ((1ULL << 48) - 1), 6, /*Upper=*/true)
+      << '{' << format_hex_no_prefix(G->Data1, 8, /*Upper=*/true)
+      << '-' << format_hex_no_prefix(G->Data2, 4, /*Upper=*/true)
+      << '-' << format_hex_no_prefix(G->Data3, 4, /*Upper=*/true)
+      << '-' << format_hex_no_prefix(G->Data4 >> 48, 4, /*Upper=*/true) << '-'
+      << format_hex_no_prefix(G->Data4 & ((1ULL << 48) - 1), 12, /*Upper=*/true)
       << '}';
 }
 
diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-1.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-1.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-2.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-2.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-3.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-3.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-4.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-4.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-5.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-5.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/Inputs/test-6.o b/llvm/test/tools/obj2yaml/COFF/Inputs/test-6.o
new file mode 100755
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/tools/obj2yaml/COFF/test-1.test b/llvm/test/tools/obj2yaml/COFF/test-1.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-1.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-1.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {00C903AB-0968-4639-84F8-7D3E719A1BE1}
diff --git a/llvm/test/tools/obj2yaml/COFF/test-2.test b/llvm/test/tools/obj2yaml/COFF/test-2.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-2.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-2.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {39B59910-0D01-4889-B930-43E2FFC14694}
diff --git a/llvm/test/tools/obj2yaml/COFF/test-3.test b/llvm/test/tools/obj2yaml/COFF/test-3.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-3.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-3.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {A03206E7-6691-415E-A241-0B5A0D0EE37A}
diff --git a/llvm/test/tools/obj2yaml/COFF/test-4.test b/llvm/test/tools/obj2yaml/COFF/test-4.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-4.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-4.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {1DD12373-03EB-4522-B3D7-07B483F45F06}
diff --git a/llvm/test/tools/obj2yaml/COFF/test-5.test b/llvm/test/tools/obj2yaml/COFF/test-5.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-5.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-5.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {0B162ECA-2764-472E-B26B-DBDEA88F3B01}
diff --git a/llvm/test/tools/obj2yaml/COFF/test-6.test b/llvm/test/tools/obj2yaml/COFF/test-6.test
new file mode 100755
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/COFF/test-6.test
@@ -0,0 +1,4 @@
+# RUN: obj2yaml %S/Inputs/test-6.o | yaml2obj -o %t.o
+# RUN: llvm-pdbutil dump --types %t.o | FileCheck %s -check-prefix=ALL
+
+# ALL: {{.*}} guid = {EA30BF0A-0A80-4424-8315-AFDD8F448DE2}
diff --git a/llvm/unittests/DebugInfo/CodeView/CMakeLists.txt b/llvm/unittests/DebugInfo/CodeView/CMakeLists.txt
--- a/llvm/unittests/DebugInfo/CodeView/CMakeLists.txt
+++ b/llvm/unittests/DebugInfo/CodeView/CMakeLists.txt
@@ -3,6 +3,7 @@
   )
 
 add_llvm_unittest(DebugInfoCodeViewTests
+  GUIDFormatTest.cpp
   RandomAccessVisitorTest.cpp
   TypeHashingTest.cpp
   TypeIndexDiscoveryTest.cpp
diff --git a/llvm/unittests/DebugInfo/CodeView/GUIDFormatTest.cpp b/llvm/unittests/DebugInfo/CodeView/GUIDFormatTest.cpp
new file mode 100755
--- /dev/null
+++ b/llvm/unittests/DebugInfo/CodeView/GUIDFormatTest.cpp
@@ -0,0 +1,143 @@
+//===- unittest/DebugInfo/CodeView/GUIDFormatTest.cpp - GUID formatting ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/DebugInfo/CodeView/Formatters.h"
+#include "llvm/DebugInfo/CodeView/GUID.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::codeview;
+
+// Variant 1 UUIDs, nowadays the most common variant, are encoded in a
+// big-endian format.
+// For example, 00112233-4455-6677-8899-aabbccddeeff is encoded as the bytes
+// 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff
+//
+// Variant 2 UUIDs, historically used in Microsoft's COM/OLE libraries, use a
+// mixed-endian format, whereby the first three components of the UUID are
+// little-endian, and the last two are big-endian.
+// For example, 00112233-4455-6677-8899-aabbccddeeff is encoded as the bytes
+// 33 22 11 00 55 44 77 66 88 99 aa bb cc dd ee ff.
+//
+// Note: Only Variant 2 UUIDs are tested.
+namespace {
+
+using GuidPair = std::pair<StringRef, GUID>;
+using GuidData = SmallVector<GuidPair>;
+
+void checkData(GuidData &Data) {
+  for (auto Item : Data) {
+    std::string GuidText(formatv("{0}", Item.second).str());
+    StringRef Scalar(GuidText);
+
+    // GUID strings are 38 characters long.
+    EXPECT_EQ(Scalar.size(), size_t(38));
+
+    // GUID must be enclosed in {}
+    EXPECT_EQ(Scalar.front(), '{');
+    EXPECT_EQ(Scalar.back(), '}');
+
+    Scalar = Scalar.substr(1, Scalar.size() - 2);
+    SmallVector<StringRef, 6> Component;
+    Scalar.split(Component, '-', 5);
+
+    // GUID must have 5 components.
+    EXPECT_EQ(Component.size(), size_t(5));
+
+    // GUID components are properly delineated with dashes.
+    EXPECT_EQ(Scalar[8], '-');
+    EXPECT_EQ(Scalar[13], '-');
+    EXPECT_EQ(Scalar[18], '-');
+    EXPECT_EQ(Scalar[23], '-');
+
+    // GUID only contains hex digits.
+    struct {
+      support::ulittle32_t Data0;
+      support::ulittle16_t Data1;
+      support::ulittle16_t Data2;
+      support::ubig16_t Data3;
+      support::ubig64_t Data4;
+    } G = {};
+    EXPECT_TRUE(to_integer(Component[0], G.Data0, 16));
+    EXPECT_TRUE(to_integer(Component[1], G.Data1, 16));
+    EXPECT_TRUE(to_integer(Component[2], G.Data2, 16));
+    EXPECT_TRUE(to_integer(Component[3], G.Data3, 16));
+    EXPECT_TRUE(to_integer(Component[4], G.Data4, 16));
+
+    // Check the values are the same.
+    EXPECT_EQ(Scalar, Item.first);
+  }
+}
+
+TEST(GUIDFormatTest, ValidateFormat) {
+  // Shifting 2 (0x00)
+  GuidData Data = {
+      // Non-zero values in all components.
+      {"11223344-5566-7788-99AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+
+      // Zero values in all components.
+      {"00000000-0000-0000-0000-000000000000",
+       {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00}},
+
+      // Shift 2 (0x00) across all components
+      {"00003344-5566-7788-99AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x00, 0x00, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11000044-5566-7788-99AA-BBCCDDEEFFAA",
+       {0x44, 0x00, 0x00, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11220000-5566-7788-99AA-BBCCDDEEFFAA",
+       {0x00, 0x00, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223300-0066-7788-99AA-BBCCDDEEFFAA",
+       {0x00, 0x33, 0x22, 0x11, 0x66, 0x00, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-0000-7788-99AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x00, 0x00, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5500-0088-99AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x00, 0x55, 0x88, 0x00, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-0000-99AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x00, 0x00, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7700-00AA-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x00, 0x77, 0x00, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7788-0000-BBCCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x00, 0x00, 0xbb, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7788-9900-00CCDDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0x00, 0x00, 0xcc,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7788-99AA-0000DDEEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0x00, 0x00,
+        0xdd, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7788-99AA-BB0000EEFFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0x00,
+        0x00, 0xee, 0xff, 0xaa}},
+      {"11223344-5566-7788-99AA-BBCC0000FFAA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0x00, 0x00, 0xff, 0xaa}},
+      {"11223344-5566-7788-99AA-BBCCDD0000AA",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0x00, 0x00, 0xaa}},
+      {"11223344-5566-7788-99AA-BBCCDDEE0000",
+       {0x44, 0x33, 0x22, 0x11, 0x66, 0x55, 0x88, 0x77, 0x99, 0xaa, 0xbb, 0xcc,
+        0xdd, 0xee, 0x00, 0x00}},
+  };
+
+  checkData(Data);
+}
+} // namespace