Index: include/llvm/MC/MCExpr.h
===================================================================
--- include/llvm/MC/MCExpr.h
+++ include/llvm/MC/MCExpr.h
@@ -280,7 +280,9 @@
     VK_Mips_PCREL_HI16,
     VK_Mips_PCREL_LO16,
 
-    VK_COFF_IMGREL32 // symbol@imgrel (image-relative)
+    VK_COFF_IMGREL32, // symbol@imgrel (image-relative)
+
+    VK_X86_64_SIZE // symbol@SIZE
   };
 
 private:
Index: lib/MC/MCExpr.cpp
===================================================================
--- lib/MC/MCExpr.cpp
+++ lib/MC/MCExpr.cpp
@@ -281,6 +281,7 @@
   case VK_Mips_PCREL_HI16: return "PCREL_HI16";
   case VK_Mips_PCREL_LO16: return "PCREL_LO16";
   case VK_COFF_IMGREL32: return "IMGREL";
+  case VK_X86_64_SIZE: return "SIZE";
   }
   llvm_unreachable("Invalid variant kind");
 }
@@ -369,6 +370,7 @@
     .Case("tlsldo", VK_ARM_TLSLDO)
     .Case("tlscall", VK_ARM_TLSCALL)
     .Case("tlsdesc", VK_ARM_TLSDESC)
+    .Case("size", VK_X86_64_SIZE)
     .Default(VK_Invalid);
 }
 
Index: lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
===================================================================
--- lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
+++ lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
@@ -123,6 +123,9 @@
         case MCSymbolRefExpr::VK_DTPOFF:
           Type = ELF::R_X86_64_DTPOFF64;
           break;
+        case MCSymbolRefExpr::VK_X86_64_SIZE:
+          Type = ELF::R_X86_64_SIZE64;
+          break;
         }
         break;
       case X86::reloc_signed_4byte:
@@ -144,6 +147,9 @@
         case MCSymbolRefExpr::VK_DTPOFF:
           Type = ELF::R_X86_64_DTPOFF32;
           break;
+        case MCSymbolRefExpr::VK_X86_64_SIZE:
+          Type = ELF::R_X86_64_SIZE64;
+          break;
         }
         break;
       case FK_Data_4:
Index: test/MC/ELF/relocation.s
===================================================================
--- test/MC/ELF/relocation.s
+++ test/MC/ELF/relocation.s
@@ -34,6 +34,10 @@
         movl  $_GLOBAL_OFFSET_TABLE_, %eax
         movabs  $_GLOBAL_OFFSET_TABLE_, %rax
 
+        movq    $foo@SIZE + 32, %rax             # R_X86_64_SIZE64
+        movq    $foo@SIZE, %rax                  # R_X86_64_SIZE64
+        movq    $foo@SIZE - 32, %rax             # R_X86_64_SIZE64
+
 // CHECK:        Section {
 // CHECK:          Name: .rela.text
 // CHECK:          Relocations [
@@ -62,6 +66,9 @@
 // CHECK-NEXT:       0x98 R_X86_64_PC32 foo 0xFFFFFFFFFFFFFFFB
 // CHECK-NEXT:       0x9D R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_ 0x1
 // CHECK-NEXT:       0xA3 R_X86_64_GOTPC64 _GLOBAL_OFFSET_TABLE_ 0x2
+// CHECK-NEXT:       0xAE R_X86_64_SIZE64 foo 0x20
+// CHECK-NEXT:       0xB5 R_X86_64_SIZE64 foo 0x0
+// CHECK-NEXT:       0xBC R_X86_64_SIZE64 foo 0xFFFFFFFFFFFFFFE0
 // CHECK-NEXT:     ]
 // CHECK-NEXT:   }