diff --git a/llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp b/llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
--- a/llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/ObjectFileInterface.cpp
@@ -150,16 +150,39 @@
 getCOFFObjectFileSymbolInfo(ExecutionSession &ES,
                             const object::COFFObjectFile &Obj) {
   MaterializationUnit::Interface I;
-
+  std::vector<Optional<object::coff_aux_section_definition>> ComdatDefs(
+      Obj.getNumberOfSections() + 1);
   for (auto &Sym : Obj.symbols()) {
     Expected<uint32_t> SymFlagsOrErr = Sym.getFlags();
     if (!SymFlagsOrErr)
       // TODO: Test this error.
       return SymFlagsOrErr.takeError();
 
-    // Skip symbols not defined in this object file.
-    if (*SymFlagsOrErr & object::BasicSymbolRef::SF_Undefined)
-      continue;
+    // Handle comdat symbols
+    auto COFFSym = Obj.getCOFFSymbol(Sym);
+    bool IsWeak = false;
+    if (auto *Def = COFFSym.getSectionDefinition()) {
+      auto Sec = Obj.getSection(COFFSym.getSectionNumber());
+      if (!Sec)
+        return Sec.takeError();
+      if (((*Sec)->Characteristics & COFF::IMAGE_SCN_LNK_COMDAT) &&
+          Def->Selection != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
+        ComdatDefs[COFFSym.getSectionNumber()] = *Def;
+        continue;
+      }
+    }
+    if (!COFF::isReservedSectionNumber(COFFSym.getSectionNumber()) &&
+        ComdatDefs[COFFSym.getSectionNumber()]) {
+      auto Def = ComdatDefs[COFFSym.getSectionNumber()];
+      if (Def->Selection != COFF::IMAGE_COMDAT_SELECT_NODUPLICATES) {
+        IsWeak = true;
+      }
+      ComdatDefs[COFFSym.getSectionNumber()] = None;
+    } else {
+      // Skip symbols not defined in this object file.
+      if (*SymFlagsOrErr & object::BasicSymbolRef::SF_Undefined)
+        continue;
+    }
 
     // Skip symbols that are not global.
     if (!(*SymFlagsOrErr & object::BasicSymbolRef::SF_Global))
@@ -180,12 +203,13 @@
     if (!SymFlags)
       return SymFlags.takeError();
     *SymFlags |= JITSymbolFlags::Exported;
-    auto COFFSym = Obj.getCOFFSymbol(Sym);
 
     // Weak external is always a function
-    if (COFFSym.isWeakExternal()) {
+    if (COFFSym.isWeakExternal())
       *SymFlags |= JITSymbolFlags::Callable;
-    }
+
+    if (IsWeak)
+      *SymFlags |= JITSymbolFlags::Weak;
 
     I.SymbolFlags[ES.intern(*Name)] = std::move(*SymFlags);
   }
diff --git a/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_duplicate.s b/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_duplicate.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_duplicate.s
@@ -0,0 +1,29 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: yaml2obj %S/Inputs/COFF_comdat_weak_def.yaml -o %t/COFF_weak_1.o
+# RUN: yaml2obj %S/Inputs/COFF_comdat_weak_def.yaml -o %t/COFF_weak_2.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc %s -o %t/COFF_main.o
+# RUN: 
+# RUN: llvm-jitlink -noexec %t/COFF_main.o %t/COFF_weak_1.o %t/COFF_weak_2.o \
+# RUN: -slab-allocate 100Kb -slab-address 0xfff00000 -slab-page-size 4096 \
+# RUN: -show-graph -noexec 2>&1 | FileCheck %s
+#
+# Check that duplicate comdat any definitions don't generate duplicate definition error.
+#
+# CHECK: section weakfunc:
+# CHECK-EMPTY:
+# CHECK-NEXT:  block 0xfff02000 size = 0x00000001, align = 16, alignment-offset = 0
+# CHECK-NEXT:    symbols:
+# CHECK-NEXT:      0xfff02000 (block + 0x00000000): size: 0x00000001, linkage: weak, scope: default, live  -   func
+# CHECK-NEXT:    no edges
+
+	.text
+
+	.def	main;
+	.scl	2;
+	.type	32;
+	.endef
+	.globl	main
+	.p2align	4, 0x90
+main:
+    callq func
+	retq
\ No newline at end of file
diff --git a/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_plus_strong.s b/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_plus_strong.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/ExecutionEngine/JITLink/X86/COFF_comdat_weak_plus_strong.s
@@ -0,0 +1,32 @@
+# FIXME: Comdat any + ordinary strong symbol should generate duplicate section error
+# XFAIL: *
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: yaml2obj %S/Inputs/COFF_comdat_weak_def.yaml -o %t/COFF_weak_1.o
+# RUN: yaml2obj %S/Inputs/COFF_strong_def.yaml -o %t/COFF_strong.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc %s -o %t/COFF_main.o
+# RUN: 
+# RUN: not llvm-jitlink -noexec %t/COFF_main.o %t/COFF_weak_1.o %t/COFF_strong.o \
+# RUN: -slab-allocate 100Kb -slab-address 0xfff00000 -slab-page-size 4096 \
+# RUN: -show-graph -noexec 2>&1 | FileCheck %s
+#
+# Check that a combination of comdat any definition and strong definition generate 
+# duplicate definition error.
+#
+# CHECK: section strongfunc:
+# CHECK-EMPTY:
+# CHECK-NEXT:  block 0xfff02000 size = 0x00000001, align = 16, alignment-offset = 0
+# CHECK-NEXT:    symbols:
+# CHECK-NEXT:      0xfff02000 (block + 0x00000000): size: 0x00000001, linkage: strong, scope: default, live  -   func
+# CHECK-NEXT:    no edges
+
+	.text
+
+	.def	main;
+	.scl	2;
+	.type	32;
+	.endef
+	.globl	main
+	.p2align	4, 0x90
+main:
+    callq func
+	retq
\ No newline at end of file
diff --git a/llvm/test/ExecutionEngine/JITLink/X86/COFF_strong_duplicate.s b/llvm/test/ExecutionEngine/JITLink/X86/COFF_strong_duplicate.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/ExecutionEngine/JITLink/X86/COFF_strong_duplicate.s
@@ -0,0 +1,23 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: yaml2obj %S/Inputs/COFF_strong_def.yaml -o %t/COFF_strong_1.o
+# RUN: yaml2obj %S/Inputs/COFF_strong_def.yaml -o %t/COFF_strong_2.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc %s -o %t/COFF_main.o
+# RUN: 
+# RUN: not llvm-jitlink -noexec %t/COFF_main.o %t/COFF_strong_1.o %t/COFF_strong_2.o \
+# RUN: -slab-allocate 100Kb -slab-address 0xfff00000 -slab-page-size 4096 \
+# RUN: -show-graph
+#
+# Check that duplicate strong definitions cause llvm-jitlink to terminate with error.
+#
+
+	.text
+
+	.def	main;
+	.scl	2;
+	.type	32;
+	.endef
+	.globl	main
+	.p2align	4, 0x90
+main:
+    callq func
+	retq
\ No newline at end of file
diff --git a/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_comdat_weak_def.yaml b/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_comdat_weak_def.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_comdat_weak_def.yaml
@@ -0,0 +1,30 @@
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            weakfunc
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     C3
+symbols:
+  - Name:            weakfunc
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        40735498
+      Number:          1
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            func
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...
diff --git a/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_strong_def.yaml b/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_strong_def.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/ExecutionEngine/JITLink/X86/Inputs/COFF_strong_def.yaml
@@ -0,0 +1,29 @@
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            strongfunc
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     C3
+symbols:
+  - Name:            strongfunc
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          1
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        40735498
+      Number:          1
+  - Name:            func
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...