Index: lld/trunk/COFF/Chunks.h
===================================================================
--- lld/trunk/COFF/Chunks.h
+++ lld/trunk/COFF/Chunks.h
@@ -243,6 +243,7 @@
   bool hasData() const override { return false; }
   uint32_t getPermissions() const override;
   StringRef getSectionName() const override { return ".bss"; }
+  void setAlign(uint32_t NewAlign);
 
 private:
   const COFFSymbolRef Sym;
Index: lld/trunk/COFF/Chunks.cpp
===================================================================
--- lld/trunk/COFF/Chunks.cpp
+++ lld/trunk/COFF/Chunks.cpp
@@ -377,6 +377,10 @@
   Align = std::min(uint64_t(32), PowerOf2Ceil(Sym.getValue()));
 }
 
+void CommonChunk::setAlign(uint32_t NewAlign) {
+  Align = std::max(Align, NewAlign);
+}
+
 uint32_t CommonChunk::getPermissions() const {
   return IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ |
          IMAGE_SCN_MEM_WRITE;
Index: lld/trunk/COFF/Config.h
===================================================================
--- lld/trunk/COFF/Config.h
+++ lld/trunk/COFF/Config.h
@@ -139,6 +139,9 @@
   StringRef ManifestUIAccess = "'false'";
   StringRef ManifestFile;
 
+  // Used for /aligncomm.
+  std::map<std::string, int> AlignComm;
+
   // Used for /failifmismatch.
   std::map<StringRef, StringRef> MustMatch;
 
Index: lld/trunk/COFF/Driver.h
===================================================================
--- lld/trunk/COFF/Driver.h
+++ lld/trunk/COFF/Driver.h
@@ -145,6 +145,7 @@
 void parseAlternateName(StringRef);
 void parseMerge(StringRef);
 void parseSection(StringRef);
+void parseAligncomm(StringRef);
 
 // Parses a string in the form of "EMBED[,=<integer>]|NO".
 void parseManifest(StringRef Arg);
Index: lld/trunk/COFF/Driver.cpp
===================================================================
--- lld/trunk/COFF/Driver.cpp
+++ lld/trunk/COFF/Driver.cpp
@@ -202,6 +202,9 @@
 
   for (auto *Arg : Args) {
     switch (Arg->getOption().getUnaliasedOption().getID()) {
+    case OPT_aligncomm:
+      parseAligncomm(Arg->getValue());
+      break;
     case OPT_alternatename:
       parseAlternateName(Arg->getValue());
       break;
@@ -899,6 +902,10 @@
   for (auto *Arg : Args.filtered(OPT_section))
     parseSection(Arg->getValue());
 
+  // Handle /aligncomm
+  for (auto *Arg : Args.filtered(OPT_aligncomm))
+    parseAligncomm(Arg->getValue());
+
   // Handle /manifestdependency. This enables /manifest unless /manifest:no is
   // also passed.
   if (auto *Arg = Args.getLastArg(OPT_manifestdependency)) {
@@ -1158,6 +1165,23 @@
     assignExportOrdinals();
   }
 
+  // Set extra alignment for .comm symbols
+  for (auto Pair : Config->AlignComm) {
+    StringRef Name = Pair.first;
+    int Align = Pair.second;
+    Symbol *Sym = Symtab.find(Name);
+    if (!Sym) {
+      warn("/aligncomm symbol " + Name + " not found");
+      continue;
+    }
+    auto *DC = dyn_cast<DefinedCommon>(Sym->body());
+    if (!DC) {
+      warn("/aligncomm symbol " + Name + " of wrong kind");
+      continue;
+    }
+    DC->getChunk()->setAlign(Align);
+  }
+
   // Windows specific -- Create a side-by-side manifest file.
   if (Config->Manifest == Configuration::SideBySide)
     createSideBySideManifest();
Index: lld/trunk/COFF/DriverUtils.cpp
===================================================================
--- lld/trunk/COFF/DriverUtils.cpp
+++ lld/trunk/COFF/DriverUtils.cpp
@@ -221,6 +221,22 @@
   Config->Section[Name] = parseSectionAttributes(Attrs);
 }
 
+// Parses /aligncomm option argument.
+void parseAligncomm(StringRef S) {
+  StringRef Name, Align;
+  std::tie(Name, Align) = S.split(',');
+  if (Name.empty() || Align.empty()) {
+    error("/aligncomm: invalid argument: " + S);
+    return;
+  }
+  int V;
+  if (Align.getAsInteger(0, V)) {
+    error("/aligncomm: invalid argument: " + S);
+    return;
+  }
+  Config->AlignComm[Name] = std::max(Config->AlignComm[Name], 1 << V);
+}
+
 // Parses a string in the form of "EMBED[,=<integer>]|NO".
 // Results are directly written to Config.
 void parseManifest(StringRef Arg) {
Index: lld/trunk/COFF/Options.td
===================================================================
--- lld/trunk/COFF/Options.td
+++ lld/trunk/COFF/Options.td
@@ -16,6 +16,7 @@
 }
 
 def align   : P<"align", "Section alignment">;
+def aligncomm : P<"aligncomm", "Set common symbol alignment">;
 def alternatename : P<"alternatename", "Define weak alias">;
 def base    : P<"base", "Base address of the program">;
 def defaultlib : P<"defaultlib", "Add the library to the list of input files">;
Index: lld/trunk/COFF/Symbols.h
===================================================================
--- lld/trunk/COFF/Symbols.h
+++ lld/trunk/COFF/Symbols.h
@@ -182,7 +182,7 @@
   }
 
   uint64_t getRVA() { return Data->getRVA(); }
-  Chunk *getChunk() { return Data; }
+  CommonChunk *getChunk() { return Data; }
 
 private:
   friend SymbolTable;
Index: lld/trunk/test/COFF/common-alignment.test
===================================================================
--- lld/trunk/test/COFF/common-alignment.test
+++ lld/trunk/test/COFF/common-alignment.test
@@ -0,0 +1,78 @@
+# REQUIRES: x86
+# RUN: yaml2obj %s > %t.obj
+# RUN: lld-link /out:%t.exe /entry:main %t.obj %t.obj
+# RUN: llvm-objdump -d %t.exe | FileCheck %s
+
+# Operands of B8 (MOV EAX) are common symbols
+# CHECK: 3000: b8 00 10 00 40
+# CHECK: 3005: b8 10 10 00 40
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     b800000000b800000000
+    Relocations:
+      - VirtualAddress:  1
+        SymbolName:      bssdata4
+        Type:            IMAGE_REL_AMD64_ADDR32
+      - VirtualAddress:  6
+        SymbolName:      bssdata4_align16
+        Type:            IMAGE_REL_AMD64_ADDR32
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     03000000
+  - Name:            .drectve
+    Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
+    Alignment:       1
+    SectionData:     202d616c69676e636f6d6d3a62737364617461345f616c69676e31362c340a  # -aligncomm:bssdata4_align16,4
+
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          0
+      NumberOfRelocations: 5
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            .data
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          4
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            main
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            bssdata4
+    Value:           4
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            bssdata4_align16
+    Value:           4
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...