diff --git a/llvm/include/llvm/BinaryFormat/COFF.h b/llvm/include/llvm/BinaryFormat/COFF.h
--- a/llvm/include/llvm/BinaryFormat/COFF.h
+++ b/llvm/include/llvm/BinaryFormat/COFF.h
@@ -98,6 +98,7 @@
   IMAGE_FILE_MACHINE_ARM = 0x1C0,
   IMAGE_FILE_MACHINE_ARMNT = 0x1C4,
   IMAGE_FILE_MACHINE_ARM64 = 0xAA64,
+  IMAGE_FILE_MACHINE_ARM64EC = 0xA641,
   IMAGE_FILE_MACHINE_EBC = 0xEBC,
   IMAGE_FILE_MACHINE_I386 = 0x14C,
   IMAGE_FILE_MACHINE_IA64 = 0x200,
diff --git a/llvm/lib/BinaryFormat/Magic.cpp b/llvm/lib/BinaryFormat/Magic.cpp
--- a/llvm/lib/BinaryFormat/Magic.cpp
+++ b/llvm/lib/BinaryFormat/Magic.cpp
@@ -231,6 +231,11 @@
       return file_magic::dxcontainer_object;
     break;
 
+  case 0x41: // ARM64EC windows
+    if (Magic[1] == char(0xA6))
+      return file_magic::coff_object;
+    break;
+
   default:
     break;
   }
diff --git a/llvm/lib/Object/COFFObjectFile.cpp b/llvm/lib/Object/COFFObjectFile.cpp
--- a/llvm/lib/Object/COFFObjectFile.cpp
+++ b/llvm/lib/Object/COFFObjectFile.cpp
@@ -977,6 +977,8 @@
     return "COFF-ARM";
   case COFF::IMAGE_FILE_MACHINE_ARM64:
     return "COFF-ARM64";
+  case COFF::IMAGE_FILE_MACHINE_ARM64EC:
+    return "COFF-ARM64EC";
   default:
     return "COFF-<unknown arch>";
   }
@@ -991,6 +993,7 @@
   case COFF::IMAGE_FILE_MACHINE_ARMNT:
     return Triple::thumb;
   case COFF::IMAGE_FILE_MACHINE_ARM64:
+  case COFF::IMAGE_FILE_MACHINE_ARM64EC:
     return Triple::aarch64;
   default:
     return Triple::UnknownArch;
@@ -1283,6 +1286,7 @@
     }
     break;
   case COFF::IMAGE_FILE_MACHINE_ARM64:
+  case COFF::IMAGE_FILE_MACHINE_ARM64EC:
     switch (Type) {
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ABSOLUTE);
     LLVM_COFF_SWITCH_RELOC_TYPE_NAME(IMAGE_REL_ARM64_ADDR32);
@@ -1865,6 +1869,7 @@
       RVAReloc = COFF::IMAGE_REL_ARM_ADDR32NB;
       break;
     case COFF::IMAGE_FILE_MACHINE_ARM64:
+    case COFF::IMAGE_FILE_MACHINE_ARM64EC:
       RVAReloc = COFF::IMAGE_REL_ARM64_ADDR32NB;
       break;
     default:
diff --git a/llvm/lib/ObjectYAML/COFFYAML.cpp b/llvm/lib/ObjectYAML/COFFYAML.cpp
--- a/llvm/lib/ObjectYAML/COFFYAML.cpp
+++ b/llvm/lib/ObjectYAML/COFFYAML.cpp
@@ -65,6 +65,7 @@
   ECase(IMAGE_FILE_MACHINE_ARM);
   ECase(IMAGE_FILE_MACHINE_ARMNT);
   ECase(IMAGE_FILE_MACHINE_ARM64);
+  ECase(IMAGE_FILE_MACHINE_ARM64EC);
   ECase(IMAGE_FILE_MACHINE_EBC);
   ECase(IMAGE_FILE_MACHINE_I386);
   ECase(IMAGE_FILE_MACHINE_IA64);
@@ -75,6 +76,9 @@
   ECase(IMAGE_FILE_MACHINE_POWERPC);
   ECase(IMAGE_FILE_MACHINE_POWERPCFP);
   ECase(IMAGE_FILE_MACHINE_R4000);
+  ECase(IMAGE_FILE_MACHINE_RISCV32);
+  ECase(IMAGE_FILE_MACHINE_RISCV64);
+  ECase(IMAGE_FILE_MACHINE_RISCV128);
   ECase(IMAGE_FILE_MACHINE_SH3);
   ECase(IMAGE_FILE_MACHINE_SH3DSP);
   ECase(IMAGE_FILE_MACHINE_SH4);
diff --git a/llvm/test/tools/llvm-readobj/COFF/arm64ec.yaml b/llvm/test/tools/llvm-readobj/COFF/arm64ec.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-readobj/COFF/arm64ec.yaml
@@ -0,0 +1,27 @@
+# RUN: yaml2obj < %s | llvm-readobj - --file-headers | FileCheck %s
+# Check we can process a simple arm64ec file.
+# CHECK: Format: COFF-ARM64EC
+# CHECK: Machine: IMAGE_FILE_MACHINE_ARM64EC (0xA641)
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARM64EC
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     ''
+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: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+...
diff --git a/llvm/tools/llvm-readobj/COFFDumper.cpp b/llvm/tools/llvm-readobj/COFFDumper.cpp
--- a/llvm/tools/llvm-readobj/COFFDumper.cpp
+++ b/llvm/tools/llvm-readobj/COFFDumper.cpp
@@ -344,6 +344,7 @@
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_AMD64    ),
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_ARM      ),
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_ARM64    ),
+  LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_ARM64EC  ),
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_ARMNT    ),
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_EBC      ),
   LLVM_READOBJ_ENUM_ENT(COFF, IMAGE_FILE_MACHINE_I386     ),
@@ -1616,9 +1617,10 @@
     break;
   }
   case COFF::IMAGE_FILE_MACHINE_ARM64:
+  case COFF::IMAGE_FILE_MACHINE_ARM64EC:
   case COFF::IMAGE_FILE_MACHINE_ARMNT: {
-    ARM::WinEH::Decoder Decoder(W, Obj->getMachine() ==
-                                       COFF::IMAGE_FILE_MACHINE_ARM64);
+    ARM::WinEH::Decoder Decoder(W, Obj->getMachine() !=
+                                       COFF::IMAGE_FILE_MACHINE_ARMNT);
     // TODO Propagate the error.
     consumeError(Decoder.dumpProcedureData(*Obj));
     break;