https://github.com/cjacek updated 
https://github.com/llvm/llvm-project/pull/202740

>From ebc5a77ce0fd36fa7a6ff6bc0bb3850fc9b66425 Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Fri, 22 May 2026 22:39:11 +0200
Subject: [PATCH 1/6] [Object][COFF] Introduce the .llvm.arm64x section

Introduce a new extension section allowing the embedding of ARM64EC
object files inside native ARM64 object files. Its content consists
of an entire, valid ARM64EC COFF object file.
---
 llvm/include/llvm/Object/COFF.h               |   3 +
 llvm/lib/Object/COFFObjectFile.cpp            |  22 ++++
 .../llvm-readobj/COFF/arm64x-hybridobj.yaml   | 102 ++++++++++++++++++
 llvm/tools/llvm-readobj/llvm-readobj.cpp      |  11 +-
 4 files changed, 135 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/tools/llvm-readobj/COFF/arm64x-hybridobj.yaml

diff --git a/llvm/include/llvm/Object/COFF.h b/llvm/include/llvm/Object/COFF.h
index ed2addbc69487..ac8c6abd7e027 100644
--- a/llvm/include/llvm/Object/COFF.h
+++ b/llvm/include/llvm/Object/COFF.h
@@ -877,6 +877,8 @@ struct coff_dynamic_relocation64_v2 {
   support::ulittle32_t Flags;
 };
 
+static constexpr StringLiteral kArm64XSectionName = ".llvm.arm64x";
+
 class LLVM_ABI COFFObjectFile : public ObjectFile {
 private:
   COFFObjectFile(MemoryBufferRef Object);
@@ -1100,6 +1102,7 @@ class LLVM_ABI COFFObjectFile : public ObjectFile {
     return SubtargetFeatures();
   }
   std::unique_ptr<MemoryBuffer> getHybridObjectView() const;
+  std::optional<MemoryBufferRef> getHybridObjectSection() const;
 
   import_directory_iterator import_directory_begin() const;
   import_directory_iterator import_directory_end() const;
diff --git a/llvm/lib/Object/COFFObjectFile.cpp 
b/llvm/lib/Object/COFFObjectFile.cpp
index 14a2343811a38..e321cd8918527 100644
--- a/llvm/lib/Object/COFFObjectFile.cpp
+++ b/llvm/lib/Object/COFFObjectFile.cpp
@@ -1560,6 +1560,28 @@ std::unique_ptr<MemoryBuffer> 
COFFObjectFile::getHybridObjectView() const {
   return HybridView;
 }
 
+std::optional<MemoryBufferRef> COFFObjectFile::getHybridObjectSection() const {
+  if (getDOSHeader() || getMachine() != COFF::IMAGE_FILE_MACHINE_ARM64)
+    return std::nullopt;
+
+  // Search the .llvm.arm64x section, which may be used to embed a full ARM64EC
+  // object file into an ARM64 object file.
+  for (const SectionRef &S : sections()) {
+    Expected<StringRef> Name = S.getName();
+    if (errorToBool(Name.takeError()))
+      return std::nullopt;
+
+    if (*Name == kArm64XSectionName) {
+      Expected<StringRef> ContentsOrErr = S.getContents();
+      if (errorToBool(ContentsOrErr.takeError()))
+        return std::nullopt;
+      return MemoryBufferRef(*ContentsOrErr, getFileName());
+    }
+  }
+
+  return std::nullopt;
+}
+
 bool ImportDirectoryEntryRef::
 operator==(const ImportDirectoryEntryRef &Other) const {
   return ImportTable == Other.ImportTable && Index == Other.Index;
diff --git a/llvm/test/tools/llvm-readobj/COFF/arm64x-hybridobj.yaml 
b/llvm/test/tools/llvm-readobj/COFF/arm64x-hybridobj.yaml
new file mode 100644
index 0000000000000..bd5d07e23f51f
--- /dev/null
+++ b/llvm/test/tools/llvm-readobj/COFF/arm64x-hybridobj.yaml
@@ -0,0 +1,102 @@
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64 %s -o %t-aarch64.o
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64EC %s -o %t-arm64ec.o
+# RUN: llvm-objcopy --add-section=.llvm.arm64x=%t-arm64ec.o 
--set-section-flags=.llvm.arm64x=debug %t-aarch64.o %t.o
+# RUN: llvm-readobj --sections %t.o | FileCheck %s
+
+# CHECK:      Format: COFF-ARM64
+# CHECK-NEXT: Arch: aarch64
+# CHECK-NEXT: AddressSize: 64bit
+# CHECK-NEXT: Sections [
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Number: 1
+# CHECK-NEXT:     Name: .data (2E 64 61 74 61 00 00 00)
+# CHECK-NEXT:     VirtualSize: 0x0
+# CHECK-NEXT:     VirtualAddress: 0x0
+# CHECK-NEXT:     RawDataSize: 4
+# CHECK-NEXT:     PointerToRawData: 0x64
+# CHECK-NEXT:     PointerToRelocations: 0x0
+# CHECK-NEXT:     PointerToLineNumbers: 0x0
+# CHECK-NEXT:     RelocationCount: 0
+# CHECK-NEXT:     LineNumberCount: 0
+# CHECK-NEXT:     Characteristics [ (0xC0300040)
+# CHECK-NEXT:       IMAGE_SCN_ALIGN_4BYTES (0x300000)
+# CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA (0x40)
+# CHECK-NEXT:       IMAGE_SCN_MEM_READ (0x40000000)
+# CHECK-NEXT:       IMAGE_SCN_MEM_WRITE (0x80000000)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {
+# CHECK-NEXT:     Number: 2
+# CHECK-NEXT:     Name: .llvm.arm64x (2F 34 00 00 00 00 00 00)
+# CHECK-NEXT:     VirtualSize: 0x7A
+# CHECK-NEXT:     VirtualAddress: 0x0
+# CHECK-NEXT:     RawDataSize: 122
+# CHECK-NEXT:     PointerToRawData: 0x68
+# CHECK-NEXT:     PointerToRelocations: 0x0
+# CHECK-NEXT:     PointerToLineNumbers: 0x0
+# CHECK-NEXT:     RelocationCount: 0
+# CHECK-NEXT:     LineNumberCount: 0
+# CHECK-NEXT:     Characteristics [ (0xC2000040)
+# CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA (0x40)
+# CHECK-NEXT:       IMAGE_SCN_MEM_DISCARDABLE (0x2000000)
+# CHECK-NEXT:       IMAGE_SCN_MEM_READ (0x40000000)
+# CHECK-NEXT:       IMAGE_SCN_MEM_WRITE (0x80000000)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+# CHECK-NEXT: HybridObject {
+# CHECK:        Format: COFF-ARM64EC
+# CHECK-NEXT:   Arch: aarch64
+# CHECK-NEXT:   AddressSize: 64bit
+# CHECK-NEXT:   Sections [
+# CHECK-NEXT:     Section {
+# CHECK-NEXT:       Number: 1
+# CHECK-NEXT:       Name: .data (2E 64 61 74 61 00 00 00)
+# CHECK-NEXT:       VirtualSize: 0x0
+# CHECK-NEXT:       VirtualAddress: 0x0
+# CHECK-NEXT:       RawDataSize: 4
+# CHECK-NEXT:       PointerToRawData: 0x3C
+# CHECK-NEXT:       PointerToRelocations: 0x0
+# CHECK-NEXT:       PointerToLineNumbers: 0x0
+# CHECK-NEXT:       RelocationCount: 0
+# CHECK-NEXT:       LineNumberCount: 0
+# CHECK-NEXT:       Characteristics [ (0xC0300040)
+# CHECK-NEXT:         IMAGE_SCN_ALIGN_4BYTES (0x300000)
+# CHECK-NEXT:         IMAGE_SCN_CNT_INITIALIZED_DATA (0x40)
+# CHECK-NEXT:         IMAGE_SCN_MEM_READ (0x40000000)
+# CHECK-NEXT:         IMAGE_SCN_MEM_WRITE (0x80000000)
+# CHECK-NEXT:       ]
+# CHECK-NEXT:     }
+# CHECK-NEXT:   ]
+# CHECK-NEXT: }
+
+--- !COFF
+header:
+  Machine:         [[MACHINE]]
+  Characteristics: [  ]
+sections:
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, 
IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     '00000000'
+    SizeOfRawData:   4
+symbols:
+  - Name:            .data
+    Value:           0
+    SectionNumber:   1
+    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:          2
+  - Name:            sym
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...
diff --git a/llvm/tools/llvm-readobj/llvm-readobj.cpp 
b/llvm/tools/llvm-readobj/llvm-readobj.cpp
index fa56e3e48e58c..cfb51c18b8484 100644
--- a/llvm/tools/llvm-readobj/llvm-readobj.cpp
+++ b/llvm/tools/llvm-readobj/llvm-readobj.cpp
@@ -604,11 +604,16 @@ static void dumpCOFFObject(COFFObjectFile *Obj, 
ScopedPrinter &Writer) {
   dumpObject(*Obj, Writer);
 
   // Dump a hybrid object when available.
-  std::unique_ptr<MemoryBuffer> HybridView = Obj->getHybridObjectView();
-  if (!HybridView)
+  MemoryBufferRef HybridView;
+  std::unique_ptr<MemoryBuffer> HybridViewBuf;
+  if (std::optional<MemoryBufferRef> HybridSec = Obj->getHybridObjectSection())
+    HybridView = *HybridSec;
+  else if ((HybridViewBuf = Obj->getHybridObjectView()))
+    HybridView = HybridViewBuf->getMemBufferRef();
+  else
     return;
   Expected<std::unique_ptr<COFFObjectFile>> HybridObjOrErr =
-      COFFObjectFile::create(*HybridView);
+      COFFObjectFile::create(HybridView);
   if (!HybridObjOrErr)
     reportError(HybridObjOrErr.takeError(), Obj->getFileName().str());
   DictScope D(Writer, "HybridObject");

>From 168d83b4d476a49757b8ea3bd06e4e3aa7a449ad Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Tue, 26 May 2026 16:45:40 +0200
Subject: [PATCH 2/6] [Object][ArchiveWriter] Factor out MemberData allocation

Factor out MemberData allocation in preparation for handling hybrid
object files, which may require creating additional archive members.
---
 llvm/lib/Object/ArchiveWriter.cpp | 64 ++++++++++++++-----------------
 1 file changed, 29 insertions(+), 35 deletions(-)

diff --git a/llvm/lib/Object/ArchiveWriter.cpp 
b/llvm/lib/Object/ArchiveWriter.cpp
index 4610fb4303274..584a5c2c597e8 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -338,6 +338,7 @@ struct MemberData {
   StringRef Padding;
   uint64_t PreHeadPadSize = 0;
   std::unique_ptr<SymbolicFile> SymFile = nullptr;
+  const NewArchiveMember *NewMember = nullptr;
 };
 } // namespace
 
@@ -783,7 +784,6 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
                   LLVMContext &Context, ArrayRef<NewArchiveMember> NewMembers,
                   std::optional<bool> IsEC, function_ref<void(Error)> Warn) {
   static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', 
'\n'};
-  uint64_t MemHeadPadSize = 0;
   uint64_t Pos =
       isAIXBigArchive(Kind) ? sizeof(object::BigArchive::FixLenHdr) : 0;
 
@@ -845,17 +845,18 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
       Entry.second = Entry.second > 1 ? 1 : 0;
   }
 
-  std::vector<std::unique_ptr<SymbolicFile>> SymFiles;
+  for (const NewArchiveMember &M : NewMembers) {
+    MemberData &D = Ret.emplace_back();
+    D.NewMember = &M;
 
-  if (NeedSymbols != SymtabWritingMode::NoSymtab || isAIXBigArchive(Kind)) {
-    for (const NewArchiveMember &M : NewMembers) {
+    if (NeedSymbols != SymtabWritingMode::NoSymtab || isAIXBigArchive(Kind)) {
       Expected<std::unique_ptr<SymbolicFile>> SymFileOrErr = getSymbolicFile(
           M.Buf->getMemBufferRef(), Context, Kind, [&](Error Err) {
             Warn(createFileError(M.MemberName, std::move(Err)));
           });
       if (!SymFileOrErr)
         return createFileError(M.MemberName, SymFileOrErr.takeError());
-      SymFiles.push_back(std::move(*SymFileOrErr));
+      D.SymFile = std::move(*SymFileOrErr);
     }
   }
 
@@ -868,13 +869,13 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
       // AMD64). This may be a single ARM64EC object, but may also be separate
       // ARM64 and AMD64 objects.
       bool HaveArm64 = false, HaveEC = false;
-      for (std::unique_ptr<SymbolicFile> &SymFile : SymFiles) {
-        if (!SymFile)
+      for (const MemberData &D : Ret) {
+        if (!D.SymFile)
           continue;
         if (!HaveArm64)
-          HaveArm64 = isAnyArm64COFF(*SymFile);
+          HaveArm64 = isAnyArm64COFF(*D.SymFile);
         if (!HaveEC)
-          HaveEC = isECObject(*SymFile);
+          HaveEC = isECObject(*D.SymFile);
         if (HaveArm64 && HaveEC) {
           SymMap->UseECMap = true;
           break;
@@ -888,23 +889,23 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
   uint64_t PrevOffset = 0;
   uint64_t NextMemHeadPadSize = 0;
 
-  for (uint32_t Index = 0; Index < NewMembers.size(); ++Index) {
-    const NewArchiveMember *M = &NewMembers[Index];
-    std::string Header;
-    raw_string_ostream Out(Header);
+  for (uint32_t Index = 0; Index < Ret.size(); ++Index) {
+    MemberData &D = Ret[Index];
+    const NewArchiveMember *M = D.NewMember;
+    raw_string_ostream Out(D.Header);
 
     MemoryBufferRef Buf = M->Buf->getMemBufferRef();
-    StringRef Data = Thin ? "" : Buf.getBuffer();
+    D.Data = Thin ? "" : Buf.getBuffer();
 
     // ld64 expects the members to be 8-byte aligned for 64-bit content and at
     // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
     // uniformly.  This matches the behaviour with cctools and ensures that 
ld64
     // is happy with archives that we generate.
     unsigned MemberPadding =
-        isDarwin(Kind) ? offsetToAlignment(Data.size(), Align(8)) : 0;
+        isDarwin(Kind) ? offsetToAlignment(D.Data.size(), Align(8)) : 0;
     unsigned TailPadding =
-        offsetToAlignment(Data.size() + MemberPadding, Align(2));
-    StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
+        offsetToAlignment(D.Data.size() + MemberPadding, Align(2));
+    D.Padding = StringRef(PaddingData, MemberPadding + TailPadding);
 
     sys::TimePoint<std::chrono::seconds> ModTime;
     if (UniqueTimestamps)
@@ -921,36 +922,32 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
           std::move(StringMsg), object::object_error::parse_failed);
     }
 
-    std::unique_ptr<SymbolicFile> CurSymFile;
-    if (!SymFiles.empty())
-      CurSymFile = std::move(SymFiles[Index]);
-
     // In the big archive file format, we need to calculate and include the 
next
     // member offset and previous member offset in the file member header.
     if (isAIXBigArchive(Kind)) {
       uint64_t OffsetToMemData = Pos + sizeof(object::BigArMemHdrType) +
                                  alignTo(M->MemberName.size(), 2);
 
-      if (M == NewMembers.begin())
+      if (Index == 0)
         NextMemHeadPadSize =
             alignToPowerOf2(OffsetToMemData,
-                            getMemberAlignment(CurSymFile.get())) -
+                            getMemberAlignment(D.SymFile.get())) -
             OffsetToMemData;
 
-      MemHeadPadSize = NextMemHeadPadSize;
-      Pos += MemHeadPadSize;
+      D.PreHeadPadSize = NextMemHeadPadSize;
+      Pos += D.PreHeadPadSize;
       uint64_t NextOffset = Pos + sizeof(object::BigArMemHdrType) +
                             alignTo(M->MemberName.size(), 2) + alignTo(Size, 
2);
 
       // If there is another member file after this, we need to calculate the
       // padding before the header.
-      if (Index + 1 != SymFiles.size()) {
+      if (Index + 1 != Ret.size()) {
         uint64_t OffsetToNextMemData =
             NextOffset + sizeof(object::BigArMemHdrType) +
-            alignTo(NewMembers[Index + 1].MemberName.size(), 2);
+            alignTo(Ret[Index + 1].NewMember->MemberName.size(), 2);
         NextMemHeadPadSize =
             alignToPowerOf2(OffsetToNextMemData,
-                            getMemberAlignment(SymFiles[Index + 1].get())) -
+                            getMemberAlignment(Ret[Index + 1].SymFile.get())) -
             OffsetToNextMemData;
         NextOffset += NextMemHeadPadSize;
       }
@@ -962,20 +959,17 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
                         ModTime, Size);
     }
 
-    std::vector<unsigned> Symbols;
     if (NeedSymbols != SymtabWritingMode::NoSymtab) {
       Expected<std::vector<unsigned>> SymbolsOrErr =
-          getSymbols(CurSymFile.get(), Index + 1, SymNames, SymMap);
+          getSymbols(D.SymFile.get(), Index + 1, SymNames, SymMap);
       if (!SymbolsOrErr)
         return createFileError(M->MemberName, SymbolsOrErr.takeError());
-      Symbols = std::move(*SymbolsOrErr);
-      if (CurSymFile)
+      D.Symbols = std::move(*SymbolsOrErr);
+      if (D.SymFile)
         HasObject = true;
     }
 
-    Pos += Header.size() + Data.size() + Padding.size();
-    Ret.push_back({std::move(Symbols), std::move(Header), Data, Padding,
-                   MemHeadPadSize, std::move(CurSymFile)});
+    Pos += D.Header.size() + D.Data.size() + D.Padding.size();
   }
   // If there are no symbols, emit an empty symbol table, to satisfy Solaris
   // tools, older versions of which expect a symbol table in a non-empty

>From 9404f0016d39b15450e218db751066e68bf41099 Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Wed, 27 May 2026 16:07:54 +0200
Subject: [PATCH 3/6] [Archive][COFF] Split hybrid COFF files when adding them
 to an archive

Create a separate member for the embedded hybrid object so that it's
properly reflected in the archive's symbol map and can be correctly
processed by tools unaware of multi-arch object files. Prefix the
embedded member name with 'llvm.arm64x/' to avoid name collisions.

We could also strip the .llvm.arm64x section from the original file.
I have a draft patch doing that I plan as a follow-up. However, that
is mostly an optimization, as the original file remains a valid ARM64
file regardless.
---
 llvm/lib/Object/ArchiveWriter.cpp             | 55 +++++++++++++------
 llvm/test/tools/llvm-ar/arm64x-hybridobj.yaml | 50 +++++++++++++++++
 .../test/tools/llvm-lib/arm64x-hybridobj.yaml | 49 +++++++++++++++++
 3 files changed, 138 insertions(+), 16 deletions(-)
 create mode 100644 llvm/test/tools/llvm-ar/arm64x-hybridobj.yaml
 create mode 100644 llvm/test/tools/llvm-lib/arm64x-hybridobj.yaml

diff --git a/llvm/lib/Object/ArchiveWriter.cpp 
b/llvm/lib/Object/ArchiveWriter.cpp
index 584a5c2c597e8..cc873fa8cb68a 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -301,24 +301,24 @@ static bool is64BitKind(object::Archive::Kind Kind) {
 static void
 printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable,
                   StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind,
-                  bool Thin, const NewArchiveMember &M,
+                  bool Thin, const NewArchiveMember &M, StringRef MemberName,
                   sys::TimePoint<std::chrono::seconds> ModTime, uint64_t Size) 
{
   if (isBSDLike(Kind))
-    return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
+    return printBSDMemberHeader(Out, Pos, MemberName, ModTime, M.UID, M.GID,
                                 M.Perms, Size);
-  if (!useStringTable(Thin, M.MemberName))
-    return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
+  if (!useStringTable(Thin, MemberName))
+    return printGNUSmallMemberHeader(Out, MemberName, ModTime, M.UID, M.GID,
                                      M.Perms, Size);
   Out << '/';
   uint64_t NamePos;
   if (Thin) {
     NamePos = StringTable.tell();
-    StringTable << M.MemberName << "/\n";
+    StringTable << MemberName << "/\n";
   } else {
-    auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
+    auto Insertion = MemberNames.insert({MemberName, uint64_t(0)});
     if (Insertion.second) {
       Insertion.first->second = StringTable.tell();
-      StringTable << M.MemberName;
+      StringTable << MemberName;
       if (isCOFFArchive(Kind))
         StringTable << '\0';
       else
@@ -339,6 +339,7 @@ struct MemberData {
   uint64_t PreHeadPadSize = 0;
   std::unique_ptr<SymbolicFile> SymFile = nullptr;
   const NewArchiveMember *NewMember = nullptr;
+  std::string HybridName = "";
 };
 } // namespace
 
@@ -857,6 +858,25 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
       if (!SymFileOrErr)
         return createFileError(M.MemberName, SymFileOrErr.takeError());
       D.SymFile = std::move(*SymFileOrErr);
+
+      if (SymMap && D.SymFile.get()) {
+        auto COFFObj = dyn_cast<COFFObjectFile>(D.SymFile.get());
+        std::optional<MemoryBufferRef> HybridView;
+        if (COFFObj && (HybridView = COFFObj->getHybridObjectSection())) {
+          // Create a separate archive member for the hybrid ARM64X object.
+          MemberData &HybridData = Ret.emplace_back();
+          HybridData.NewMember = &M;
+
+          SymFileOrErr =
+              getSymbolicFile(*HybridView, Context, Kind, [&](Error Err) {
+                Warn(createFileError(M.MemberName, std::move(Err)));
+              });
+          if (!SymFileOrErr)
+            return createFileError(M.MemberName, SymFileOrErr.takeError());
+          HybridData.SymFile = std::move(*SymFileOrErr);
+          HybridData.HybridName = ("llvm.arm64x/" + M.MemberName).str();
+        }
+      }
     }
   }
 
@@ -894,7 +914,8 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
     const NewArchiveMember *M = D.NewMember;
     raw_string_ostream Out(D.Header);
 
-    MemoryBufferRef Buf = M->Buf->getMemBufferRef();
+    MemoryBufferRef Buf =
+        D.SymFile ? D.SymFile->getMemoryBufferRef() : 
M->Buf->getMemBufferRef();
     D.Data = Thin ? "" : Buf.getBuffer();
 
     // ld64 expects the members to be 8-byte aligned for 64-bit content and at
@@ -907,17 +928,19 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
         offsetToAlignment(D.Data.size() + MemberPadding, Align(2));
     D.Padding = StringRef(PaddingData, MemberPadding + TailPadding);
 
+    StringRef MemberName = D.HybridName.size() ? D.HybridName : M->MemberName;
+
     sys::TimePoint<std::chrono::seconds> ModTime;
     if (UniqueTimestamps)
       // Increment timestamp for each file of a given name.
-      ModTime = sys::toTimePoint(FilenameCount[M->MemberName]++);
+      ModTime = sys::toTimePoint(FilenameCount[MemberName]++);
     else
       ModTime = M->ModTime;
 
     uint64_t Size = Buf.getBufferSize() + MemberPadding;
     if (Size > object::Archive::MaxMemberSize) {
       std::string StringMsg =
-          "File " + M->MemberName.str() + " exceeds size limit";
+          "File " + MemberName.str() + " exceeds size limit";
       return make_error<object::GenericBinaryError>(
           std::move(StringMsg), object::object_error::parse_failed);
     }
@@ -925,8 +948,8 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
     // In the big archive file format, we need to calculate and include the 
next
     // member offset and previous member offset in the file member header.
     if (isAIXBigArchive(Kind)) {
-      uint64_t OffsetToMemData = Pos + sizeof(object::BigArMemHdrType) +
-                                 alignTo(M->MemberName.size(), 2);
+      uint64_t OffsetToMemData =
+          Pos + sizeof(object::BigArMemHdrType) + alignTo(MemberName.size(), 
2);
 
       if (Index == 0)
         NextMemHeadPadSize =
@@ -937,7 +960,7 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
       D.PreHeadPadSize = NextMemHeadPadSize;
       Pos += D.PreHeadPadSize;
       uint64_t NextOffset = Pos + sizeof(object::BigArMemHdrType) +
-                            alignTo(M->MemberName.size(), 2) + alignTo(Size, 
2);
+                            alignTo(MemberName.size(), 2) + alignTo(Size, 2);
 
       // If there is another member file after this, we need to calculate the
       // padding before the header.
@@ -951,19 +974,19 @@ computeMemberData(raw_ostream &StringTable, raw_ostream 
&SymNames,
             OffsetToNextMemData;
         NextOffset += NextMemHeadPadSize;
       }
-      printBigArchiveMemberHeader(Out, M->MemberName, ModTime, M->UID, M->GID,
+      printBigArchiveMemberHeader(Out, MemberName, ModTime, M->UID, M->GID,
                                   M->Perms, Size, PrevOffset, NextOffset);
       PrevOffset = Pos;
     } else {
       printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, *M,
-                        ModTime, Size);
+                        MemberName, ModTime, Size);
     }
 
     if (NeedSymbols != SymtabWritingMode::NoSymtab) {
       Expected<std::vector<unsigned>> SymbolsOrErr =
           getSymbols(D.SymFile.get(), Index + 1, SymNames, SymMap);
       if (!SymbolsOrErr)
-        return createFileError(M->MemberName, SymbolsOrErr.takeError());
+        return createFileError(MemberName, SymbolsOrErr.takeError());
       D.Symbols = std::move(*SymbolsOrErr);
       if (D.SymFile)
         HasObject = true;
diff --git a/llvm/test/tools/llvm-ar/arm64x-hybridobj.yaml 
b/llvm/test/tools/llvm-ar/arm64x-hybridobj.yaml
new file mode 100644
index 0000000000000..884489e6701a4
--- /dev/null
+++ b/llvm/test/tools/llvm-ar/arm64x-hybridobj.yaml
@@ -0,0 +1,50 @@
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64 %s -o %t-aarch64.o
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64EC %s -o %t-arm64ec.o
+# RUN: llvm-objcopy --add-section=.llvm.arm64x=%t-arm64ec.o 
--set-section-flags=.llvm.arm64x=debug %t-aarch64.o %t.o
+# RUN: rm -f %t.lib
+# RUN: llvm-ar rc %t.lib %t.o
+# RUN: llvm-nm --print-armap %t.lib | FileCheck %s
+
+# CHECK:      Archive map
+# CHECK-NEXT: sym in arm64x-hybridobj.yaml.tmp.o
+# CHECK-EMPTY:
+# CHECK-NEXT: Archive EC map
+# CHECK-NEXT: sym in llvm.arm64x/arm64x-hybridobj.yaml.tmp.o
+# CHECK-EMPTY:
+# CHECK-EMPTY:
+# CHECK-NEXT: arm64x-hybridobj.yaml.tmp.o:
+# CHECK-NEXT: 00000000 D sym
+# CHECK-EMPTY:
+# CHECK-NEXT: llvm.arm64x/arm64x-hybridobj.yaml.tmp.o:
+# CHECK-NEXT: 00000000 D sym
+
+--- !COFF
+header:
+  Machine:         [[MACHINE]]
+  Characteristics: [  ]
+sections:
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, 
IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     '00000000'
+    SizeOfRawData:   4
+symbols:
+  - Name:            .data
+    Value:           0
+    SectionNumber:   1
+    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:          2
+  - Name:            sym
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...
diff --git a/llvm/test/tools/llvm-lib/arm64x-hybridobj.yaml 
b/llvm/test/tools/llvm-lib/arm64x-hybridobj.yaml
new file mode 100644
index 0000000000000..27d4a1c444cdf
--- /dev/null
+++ b/llvm/test/tools/llvm-lib/arm64x-hybridobj.yaml
@@ -0,0 +1,49 @@
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64 %s -o %t-aarch64.o
+# RUN: yaml2obj -DMACHINE=IMAGE_FILE_MACHINE_ARM64EC %s -o %t-arm64ec.o
+# RUN: llvm-objcopy --add-section=.llvm.arm64x=%t-arm64ec.o 
--set-section-flags=.llvm.arm64x=debug %t-aarch64.o %t.o
+# RUN: llvm-lib -machine:arm64x -out:%t.lib %t.o
+# RUN: llvm-nm --print-armap %t.lib | FileCheck %s
+
+# CHECK:      Archive map
+# CHECK-NEXT: sym in {{.*}}arm64x-hybridobj.yaml.tmp.o
+# CHECK-EMPTY:
+# CHECK-NEXT: Archive EC map
+# CHECK-NEXT: sym in llvm.arm64x/{{.*}}arm64x-hybridobj.yaml.tmp.o
+# CHECK-EMPTY:
+# CHECK-EMPTY:
+# CHECK-NEXT: {{.*}}arm64x-hybridobj.yaml.tmp.o:
+# CHECK-NEXT: 00000000 D sym
+# CHECK-EMPTY:
+# CHECK-NEXT: llvm.arm64x/{{.*}}arm64x-hybridobj.yaml.tmp.o:
+# CHECK-NEXT: 00000000 D sym
+
+--- !COFF
+header:
+  Machine:         [[MACHINE]]
+  Characteristics: [  ]
+sections:
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, 
IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     '00000000'
+    SizeOfRawData:   4
+symbols:
+  - Name:            .data
+    Value:           0
+    SectionNumber:   1
+    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:          2
+  - Name:            sym
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

>From 748698c313cacc1040112f869f232089d67fb78f Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Mon, 8 Jun 2026 17:59:55 +0200
Subject: [PATCH 4/6] [LLD][COFF] Factor out addObjectFile

Avoid parsing the input COFF file twice by creating it earlier and
replacing findBitcodeInMemBuffer with findBitcodeInObject. It's also
a preparation for handling hybrid ARM64X object files.
---
 lld/COFF/Driver.cpp     | 28 +++++++++++++++++-----------
 lld/COFF/Driver.h       |  4 ++++
 lld/COFF/InputFiles.cpp | 12 +++++++++---
 lld/COFF/InputFiles.h   |  9 ++++++++-
 4 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 024cb2c95cd20..34b8c85116984 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -262,21 +262,27 @@ MemoryBufferRef 
LinkerDriver::takeBuffer(std::unique_ptr<MemoryBuffer> mb) {
   return mbref;
 }
 
-static InputFile *tryCreateFatLTOFile(COFFLinkerContext &ctx,
-                                      MemoryBufferRef mb, StringRef 
archiveName,
-                                      uint64_t offsetInArchive, bool lazy) {
+InputFile *LinkerDriver::addObjectFile(COFFLinkerContext &ctx,
+                                       MemoryBufferRef mb,
+                                       StringRef archiveName,
+                                       uint64_t offsetInArchive, bool lazy) {
+  COFFObjectFile *coffObj = ObjFile::createCOFFObject(ctx, mb);
+  InputFile *obj = nullptr;
+
   if (ctx.config.fatLTOObjects) {
     Expected<MemoryBufferRef> fatLTOData =
-        IRObjectFile::findBitcodeInMemBuffer(mb);
+        IRObjectFile::findBitcodeInObject(*coffObj);
 
     if (!errorToBool(fatLTOData.takeError())) {
-      return BitcodeFile::create(ctx, *fatLTOData, archiveName, 
offsetInArchive,
-                                 lazy);
+      obj = BitcodeFile::create(ctx, *fatLTOData, archiveName, offsetInArchive,
+                                lazy);
     }
   }
 
-  InputFile *obj = ObjFile::create(ctx, mb, lazy);
+  if (!obj)
+    obj = ObjFile::create(ctx, coffObj, lazy);
   obj->parentName = archiveName;
+  addFile(obj);
   return obj;
 }
 
@@ -323,7 +329,7 @@ void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> 
mb,
     addFile(BitcodeFile::create(ctx, mbref, "", 0, lazy));
     break;
   case file_magic::coff_object: {
-    addFile(tryCreateFatLTOFile(ctx, mbref, "", 0, lazy));
+    addObjectFile(ctx, mbref, "", 0, lazy);
     break;
   }
   case file_magic::coff_import_library:
@@ -437,9 +443,11 @@ void LinkerDriver::addArchiveBuffer(MemoryBufferRef mb, 
StringRef symName,
 
   InputFile *obj;
   if (magic == file_magic::coff_object) {
-    obj = tryCreateFatLTOFile(ctx, mb, parentName, offsetInArchive, lazy);
+    obj = addObjectFile(ctx, mb, parentName, offsetInArchive, lazy);
   } else if (magic == file_magic::bitcode) {
     obj = BitcodeFile::create(ctx, mb, parentName, offsetInArchive, lazy);
+    obj->parentName = parentName;
+    addFile(obj);
   } else if (magic == file_magic::coff_cl_gl_object) {
     Err(ctx) << mb.getBufferIdentifier()
              << ": is not a native COFF file. Recompile without /GL?";
@@ -449,8 +457,6 @@ void LinkerDriver::addArchiveBuffer(MemoryBufferRef mb, 
StringRef symName,
     return;
   }
 
-  obj->parentName = parentName;
-  addFile(obj);
   Log(ctx) << "Loaded " << obj << " for " << symName;
 }
 
diff --git a/lld/COFF/Driver.h b/lld/COFF/Driver.h
index e7a7acebc6e4c..7eea9aee279a1 100644
--- a/lld/COFF/Driver.h
+++ b/lld/COFF/Driver.h
@@ -125,6 +125,10 @@ class LinkerDriver {
 
   bool isDecorated(StringRef sym);
 
+  InputFile *addObjectFile(COFFLinkerContext &ctx, MemoryBufferRef mb,
+                           StringRef archiveName, uint64_t offsetInArchive,
+                           bool lazy);
+
   std::string getMapFile(const llvm::opt::InputArgList &args,
                          llvm::opt::OptSpecifier os,
                          llvm::opt::OptSpecifier osFile);
diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index 3821c9366c56a..a9113f8260576 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -278,7 +278,8 @@ ObjFile::ObjFile(SymbolTable &symtab, COFFObjectFile 
*coffObj, bool lazy)
     : InputFile(symtab, ObjectKind, coffObj->getMemoryBufferRef(), lazy),
       coffObj(coffObj) {}
 
-ObjFile *ObjFile::create(COFFLinkerContext &ctx, MemoryBufferRef m, bool lazy) 
{
+COFFObjectFile *ObjFile::createCOFFObject(COFFLinkerContext &ctx,
+                                          MemoryBufferRef m) {
   // Parse a memory buffer as a COFF file.
   Expected<std::unique_ptr<Binary>> bin = createBinary(m);
   if (!bin)
@@ -289,8 +290,13 @@ ObjFile *ObjFile::create(COFFLinkerContext &ctx, 
MemoryBufferRef m, bool lazy) {
     Fatal(ctx) << m.getBufferIdentifier() << " is not a COFF file";
 
   bin->release();
-  return make<ObjFile>(ctx.getSymtab(MachineTypes(obj->getMachine())), obj,
-                       lazy);
+  return obj;
+}
+
+ObjFile *ObjFile::create(COFFLinkerContext &ctx, COFFObjectFile *coffObj,
+                         bool lazy) {
+  return make<ObjFile>(ctx.getSymtab(MachineTypes(coffObj->getMachine())),
+                       coffObj, lazy);
 }
 
 void ObjFile::parseLazy() {
diff --git a/lld/COFF/InputFiles.h b/lld/COFF/InputFiles.h
index ce8bc6705e489..b9cf3bd0339c4 100644
--- a/lld/COFF/InputFiles.h
+++ b/lld/COFF/InputFiles.h
@@ -136,10 +136,17 @@ class ArchiveFile : public InputFile {
 // .obj or .o file. This may be a member of an archive file.
 class ObjFile : public InputFile {
 public:
-  static ObjFile *create(COFFLinkerContext &ctx, MemoryBufferRef mb,
+  static ObjFile *create(COFFLinkerContext &ctx, COFFObjectFile *coffObj,
                          bool lazy = false);
+  static ObjFile *create(COFFLinkerContext &ctx, MemoryBufferRef mb,
+                         bool lazy = false) {
+    return ObjFile::create(ctx, ObjFile::createCOFFObject(ctx, mb), lazy);
+  }
   explicit ObjFile(SymbolTable &symtab, COFFObjectFile *coffObj, bool lazy);
 
+  static COFFObjectFile *createCOFFObject(COFFLinkerContext &ctx,
+                                          MemoryBufferRef mb);
+
   static bool classof(const InputFile *f) { return f->kind() == ObjectKind; }
   void parse() override;
   void parseLazy();

>From 6cfd7ec80f14aefb87bc7b50e8fa0d93c0a5c904 Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Mon, 8 Jun 2026 18:02:40 +0200
Subject: [PATCH 5/6] [LLD][COFF] Add support for multi-atch ARM64X object
 files

---
 lld/COFF/Driver.cpp              | 21 ++++++++--
 lld/COFF/Driver.h                |  4 +-
 lld/test/COFF/arm64x-hybridobj.s | 71 ++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+), 6 deletions(-)
 create mode 100644 lld/test/COFF/arm64x-hybridobj.s

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 34b8c85116984..aa3b880b2418a 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -265,10 +265,21 @@ MemoryBufferRef 
LinkerDriver::takeBuffer(std::unique_ptr<MemoryBuffer> mb) {
 InputFile *LinkerDriver::addObjectFile(COFFLinkerContext &ctx,
                                        MemoryBufferRef mb,
                                        StringRef archiveName,
-                                       uint64_t offsetInArchive, bool lazy) {
+                                       uint64_t offsetInArchive, bool lazy,
+                                       bool addHybrid) {
   COFFObjectFile *coffObj = ObjFile::createCOFFObject(ctx, mb);
   InputFile *obj = nullptr;
 
+  if (addHybrid && ctx.symtab.isEC()) {
+    if (std::optional<MemoryBufferRef> hybridView =
+            coffObj->getHybridObjectSection()) {
+      InputFile *hybridObj = addObjectFile(ctx, *hybridView, archiveName,
+                                           offsetInArchive, lazy, false);
+      if (ctx.config.machine != ARM64X)
+        return hybridObj;
+    }
+  }
+
   if (ctx.config.fatLTOObjects) {
     Expected<MemoryBufferRef> fatLTOData =
         IRObjectFile::findBitcodeInObject(*coffObj);
@@ -432,7 +443,8 @@ void LinkerDriver::enqueuePath(StringRef path, bool lazy, 
InputOpt inputOpt) {
 
 void LinkerDriver::addArchiveBuffer(MemoryBufferRef mb, StringRef symName,
                                     StringRef parentName,
-                                    uint64_t offsetInArchive, bool lazy) {
+                                    uint64_t offsetInArchive, bool lazy,
+                                    bool isThin) {
   file_magic magic = identify_magic(mb.getBuffer());
   if (magic == file_magic::coff_import_library) {
     InputFile *imp = make<ImportFile>(ctx, mb);
@@ -443,7 +455,7 @@ void LinkerDriver::addArchiveBuffer(MemoryBufferRef mb, 
StringRef symName,
 
   InputFile *obj;
   if (magic == file_magic::coff_object) {
-    obj = addObjectFile(ctx, mb, parentName, offsetInArchive, lazy);
+    obj = addObjectFile(ctx, mb, parentName, offsetInArchive, lazy, isThin);
   } else if (magic == file_magic::bitcode) {
     obj = BitcodeFile::create(ctx, mb, parentName, offsetInArchive, lazy);
     obj->parentName = parentName;
@@ -466,7 +478,8 @@ void LinkerDriver::addThinArchiveBuffer(MemoryBufferRef mb, 
StringRef symName,
   // the original filename is used as the buffer identifier. This is
   // useful for DTLTO, where having the member identifier be the actual
   // path on disk enables distribution of bitcode files during ThinLTO.
-  addArchiveBuffer(mb, symName, /*parentName=*/"", /*OffsetInArchive=*/0, 
lazy);
+  addArchiveBuffer(mb, symName, /*parentName=*/"", /*OffsetInArchive=*/0, lazy,
+                   true);
 }
 
 void LinkerDriver::enqueueArchiveMember(const Archive::Child &c,
diff --git a/lld/COFF/Driver.h b/lld/COFF/Driver.h
index 7eea9aee279a1..572ed85eed35e 100644
--- a/lld/COFF/Driver.h
+++ b/lld/COFF/Driver.h
@@ -127,7 +127,7 @@ class LinkerDriver {
 
   InputFile *addObjectFile(COFFLinkerContext &ctx, MemoryBufferRef mb,
                            StringRef archiveName, uint64_t offsetInArchive,
-                           bool lazy);
+                           bool lazy, bool addHybrid = true);
 
   std::string getMapFile(const llvm::opt::InputArgList &args,
                          llvm::opt::OptSpecifier os,
@@ -183,7 +183,7 @@ class LinkerDriver {
                  bool lazy);
   void addArchiveBuffer(MemoryBufferRef mbref, StringRef symName,
                         StringRef parentName, uint64_t offsetInArchive,
-                        bool lazy);
+                        bool lazy, bool isThin = false);
   void addThinArchiveBuffer(MemoryBufferRef mbref, StringRef symName,
                             bool lazy);
 
diff --git a/lld/test/COFF/arm64x-hybridobj.s b/lld/test/COFF/arm64x-hybridobj.s
new file mode 100644
index 0000000000000..8742e8fd03b8d
--- /dev/null
+++ b/lld/test/COFF/arm64x-hybridobj.s
@@ -0,0 +1,71 @@
+// REQUIRES: aarch64
+// RUN: split-file %s %t.dir && cd %t.dir
+
+// RUN: llvm-mc -filetype=obj -triple=aarch64-windows sym.s -o sym-arm64.obj
+// RUN: llvm-mc -filetype=obj -triple=arm64ec-windows sym.s -o sym-arm64ec.obj
+// RUN: llvm-objcopy --add-section=.llvm.arm64x=sym-arm64ec.obj 
--set-section-flags=.llvm.arm64x=debug \
+// RUN:              sym-arm64.obj sym.obj
+
+// RUN: llvm-mc -filetype=obj -triple=aarch64-windows ref.s -o ref-arm64.obj
+// RUN: llvm-mc -filetype=obj -triple=arm64ec-windows ref.s -o ref-arm64ec.obj
+// RUN: llvm-objcopy --add-section=.llvm.arm64x=ref-arm64ec.obj 
--set-section-flags=.llvm.arm64x=debug \
+// RUN:              ref-arm64.obj ref.obj
+
+// RUN: llvm-mc -filetype=obj -triple=arm64ec-windows 
%S/Inputs/loadconfig-arm64ec.s -o loadconfig-arm64ec.obj
+// RUN: llvm-mc -filetype=obj -triple=aarch64-windows 
%S/Inputs/loadconfig-arm64.s -o loadconfig-arm64.obj
+// RUN: llvm-objcopy --add-section=.llvm.arm64x=loadconfig-arm64ec.obj 
--set-section-flags=.llvm.arm64x=debug \
+// RUN:              loadconfig-arm64.obj loadconfig.obj
+
+// RUN: lld-link -machine:arm64x -dll -noentry -out:out.dll sym.obj 
loadconfig.obj
+// RUN: llvm-readobj --coff-exports out.dll | FileCheck %s
+
+// RUN: lld-link -machine:arm64ec -dll -noentry -out:out-ec.dll sym.obj 
loadconfig.obj
+// RUN: lld-link -machine:arm64 -dll -noentry -out:out-native.dll sym.obj 
loadconfig.obj
+
+// RUN: llvm-ar cr sym.lib sym.obj
+// RUN: lld-link -machine:arm64x -dll -noentry -out:out2.dll ref.obj sym.lib 
loadconfig.obj
+// RUN: llvm-readobj --coff-exports out2.dll | FileCheck %s
+// RUN: lld-link -machine:arm64ec -dll -noentry -out:out-ec2.dll sym.obj 
loadconfig.obj
+// RUN: lld-link -machine:arm64 -dll -noentry -out:out-native2.dll sym.obj 
loadconfig.obj
+
+// RUN: llvm-ar cr --thin sym-thin.lib sym.obj
+// RUN: lld-link -machine:arm64x -dll -noentry -out:out3.dll ref.obj 
sym-thin.lib loadconfig.obj
+// RUN: llvm-readobj --coff-exports out3.dll | FileCheck %s
+
+// RUN: lld-link -machine:arm64x -dll -noentry -out:out4.dll ref.obj 
-start-lib sym.obj loadconfig.obj -end-lib
+// RUN: llvm-readobj --coff-exports out4.dll | FileCheck %s
+
+// RUN: lld-link -machine:arm64x -dll -noentry -out:out4.dll 
-wholearchive:sym-thin.lib loadconfig.obj
+// RUN: llvm-readobj --coff-exports out4.dll | FileCheck %s
+
+// CHECK:      Format: COFF-ARM64X
+// CHECK-NEXT: Arch: aarch64
+// CHECK-NEXT: AddressSize: 64bit
+// CHECK-NEXT: Export {
+// CHECK-NEXT:   Ordinal: 1
+// CHECK-NEXT:   Name: sym
+// CHECK-NEXT:   RVA: 0x4004
+// CHECK-NEXT: }
+// CHECK-NEXT: HybridObject {
+// CHECK-NEXT:   Format: COFF-ARM64EC
+// CHECK-NEXT:   Arch: aarch64
+// CHECK-NEXT:   AddressSize: 64bit
+// CHECK-NEXT:   Export {
+// CHECK-NEXT:     Ordinal: 1
+// CHECK-NEXT:     Name: sym
+// CHECK-NEXT:     RVA: 0x4000
+// CHECK-NEXT:   }
+// CHECK-NEXT: }
+
+#--- sym.s
+        .section .sym,"dr"
+        .globl sym
+sym:
+        .long 0
+
+        .section .drectve
+        .ascii "-export:sym"
+
+#--- ref.s
+        .data
+        .rva sym

>From 84d8dbdd34d05aa5d998a4af26b6e7f4a7404f2f Mon Sep 17 00:00:00 2001
From: Jacek Caban <[email protected]>
Date: Wed, 1 Apr 2026 16:18:07 +0200
Subject: [PATCH 6/6] [clang][ARM64X] Support compiling both native and EC
 objects with -marm64x

When -marm64x is used during the assembly phase, construct jobs for both
native and EC targets and merge their outputs using llvm-objcopy.
---
 clang/include/clang/Driver/Action.h    |  2 +-
 clang/include/clang/Options/Options.td |  2 +-
 clang/lib/Driver/Action.cpp            |  4 +--
 clang/lib/Driver/Driver.cpp            | 37 +++++++++++++++++++-------
 clang/lib/Driver/ToolChain.cpp         |  4 ++-
 clang/lib/Driver/ToolChains/MSVC.cpp   | 11 ++++++++
 clang/lib/Driver/ToolChains/MSVC.h     |  4 +++
 clang/lib/Driver/ToolChains/MinGW.cpp  | 29 ++++++++++++++++++++
 clang/lib/Driver/ToolChains/MinGW.h    | 14 ++++++++++
 clang/test/Driver/arm64x.c             |  6 +++++
 clang/test/Driver/msvc-link.c          |  4 +--
 11 files changed, 101 insertions(+), 16 deletions(-)
 create mode 100644 clang/test/Driver/arm64x.c

diff --git a/clang/include/clang/Driver/Action.h 
b/clang/include/clang/Driver/Action.h
index 67937b00f6bcf..edad2e64e8d62 100644
--- a/clang/include/clang/Driver/Action.h
+++ b/clang/include/clang/Driver/Action.h
@@ -695,7 +695,7 @@ class ObjcopyJobAction : public JobAction {
   void anchor() override;
 
 public:
-  ObjcopyJobAction(Action *Input, types::ID Type);
+  ObjcopyJobAction(ActionList &Inputs, types::ID Type);
 
   static bool classof(const Action *A) {
     return A->getKind() == ObjcopyJobClass;
diff --git a/clang/include/clang/Options/Options.td 
b/clang/include/clang/Options/Options.td
index 4fd892e58df86..23a27c4db6985 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -5410,7 +5410,7 @@ def municode : Joined<["-"], "municode">, Group<m_Group>;
 def mthreads : Joined<["-"], "mthreads">, Group<m_Group>;
 def marm64x : Joined<["-"], "marm64x">, Group<m_Group>,
   Visibility<[ClangOption, CLOption]>,
-  HelpText<"Link as a hybrid ARM64X image">;
+  HelpText<"Build as a hybrid ARM64X image">;
 def mguard_EQ : Joined<["-"], "mguard=">, Group<m_Group>,
   HelpText<"Enable or disable Control Flow Guard checks and guard tables 
emission">,
   Values<"none,cf,cf-nochecks">;
diff --git a/clang/lib/Driver/Action.cpp b/clang/lib/Driver/Action.cpp
index 72a42a6f957ee..01045a97930f8 100644
--- a/clang/lib/Driver/Action.cpp
+++ b/clang/lib/Driver/Action.cpp
@@ -472,5 +472,5 @@ BinaryTranslatorJobAction::BinaryTranslatorJobAction(Action 
*Input,
 
 void ObjcopyJobAction::anchor() {}
 
-ObjcopyJobAction::ObjcopyJobAction(Action *Input, types::ID Type)
-    : JobAction(ObjcopyJobClass, Input, Type) {}
+ObjcopyJobAction::ObjcopyJobAction(ActionList &Inputs, types::ID Type)
+    : JobAction(ObjcopyJobClass, Inputs, Type) {}
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index c2a2cd80b94b2..6ca9639276341 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -618,10 +618,9 @@ static void setZosTargetVersion(const Driver &D, 
llvm::Triple &Target,
 ///
 /// This routine provides the logic to compute a target triple from various
 /// args passed to the driver and the default triple string.
-static llvm::Triple computeTargetTriple(const Driver &D,
-                                        StringRef TargetTriple,
+static llvm::Triple computeTargetTriple(const Driver &D, StringRef 
TargetTriple,
                                         const ArgList &Args,
-                                        StringRef DarwinArchName = "") {
+                                        StringRef ArchName = "") {
   // FIXME: Already done in Compilation *Driver::BuildCompilation
   if (const Arg *A = Args.getLastArg(options::OPT_target))
     TargetTriple = A->getValue();
@@ -637,9 +636,8 @@ static llvm::Triple computeTargetTriple(const Driver &D,
   // Handle Apple-specific options available here.
   if (Target.isOSBinFormatMachO()) {
     // If an explicit Darwin arch name is given, that trumps all.
-    if (!DarwinArchName.empty()) {
-      tools::darwin::setTripleTypeForMachOArchName(Target, DarwinArchName,
-                                                   Args);
+    if (!ArchName.empty()) {
+      tools::darwin::setTripleTypeForMachOArchName(Target, ArchName, Args);
       return Target;
     }
 
@@ -648,6 +646,9 @@ static llvm::Triple computeTargetTriple(const Driver &D,
       StringRef ArchName = A->getValue();
       tools::darwin::setTripleTypeForMachOArchName(Target, ArchName, Args);
     }
+  } else if (!ArchName.empty()) {
+    Target.setArchName(ArchName);
+    return Target;
   }
 
   // Handle pseudo-target flags '-mlittle-endian'/'-EL' and
@@ -700,6 +701,11 @@ static llvm::Triple computeTargetTriple(const Driver &D,
     D.Diag(diag::err_drv_unsupported_opt_for_target)
         << A->getAsString(Args) << Target.str();
 
+  // The `-marm64x` flag is only valid for Windows targets.
+  if (Args.hasArgNoClaim(options::OPT_marm64x) && !Target.isOSWindows())
+    D.Diag(diag::err_drv_unsupported_opt_for_target)
+        << "-marm64x" << Target.str();
+
   // Handle pseudo-target flags '-m64', '-mx32', '-m32' and '-m16'.
   Arg *A = Args.getLastArg(options::OPT_m64, options::OPT_mx32,
                            options::OPT_m32, options::OPT_m16,
@@ -4808,9 +4814,11 @@ void Driver::BuildActions(Compilation &C, DerivedArgList 
&Args,
     if (TC.requiresObjcopy(Args)) {
       Action *LastAction = Actions.back();
       // llvm-objcopy expects an unvalidated DXIL container (TY_OBJECT).
-      if (LastAction->getType() == types::TY_Object)
+      if (LastAction->getType() == types::TY_Object) {
+        ActionList ObjcopyActions({LastAction});
         Actions.push_back(
-            C.MakeAction<ObjcopyJobAction>(LastAction, types::TY_Object));
+            C.MakeAction<ObjcopyJobAction>(ObjcopyActions, types::TY_Object));
+      }
     }
 
     // Call validator when -Vd not in Args.
@@ -5471,6 +5479,16 @@ Action *Driver::ConstructPhaseAction(
     return C.MakeAction<BackendJobAction>(Input, types::TY_PP_Asm);
   }
   case phases::Assemble:
+    // When -marm64x is used, construct jobs for the EC and native targets and
+    // merge them into an archive with llvm-objcopy.
+    if (Args.hasArg(options::OPT_marm64x)) {
+      Action *Act =
+          C.MakeAction<AssembleJobAction>(std::move(Input), types::TY_Object);
+      ActionList Inputs;
+      Inputs.push_back(C.MakeAction<BindArchAction>(Act, "arm64ec"));
+      Inputs.push_back(C.MakeAction<BindArchAction>(Act, "aarch64"));
+      return C.MakeAction<ObjcopyJobAction>(Inputs, types::TY_Object);
+    }
     return C.MakeAction<AssembleJobAction>(std::move(Input), types::TY_Object);
   }
 
@@ -5565,7 +5583,8 @@ void Driver::BuildJobs(Compilation &C) const {
     BuildJobsForAction(C, A, &C.getDefaultToolChain(),
                        /*BoundArch*/ StringRef(),
                        /*AtTopLevel*/ true,
-                       /*MultipleArchs*/ ArchNames.size() > 1,
+                       /*MultipleArchs*/ ArchNames.size() > 1 ||
+                           C.getArgs().hasArgNoClaim(options::OPT_marm64x),
                        /*LinkingOutput*/ LinkingOutput, CachedResults,
                        /*TargetDeviceOffloadKind*/ Action::OFK_None);
   }
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index ccfc022f79427..eb1878594a779 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -776,9 +776,11 @@ Tool *ToolChain::getTool(Action::ActionClass AC) const {
   case Action::VerifyDebugInfoJobClass:
   case Action::BinaryAnalyzeJobClass:
   case Action::BinaryTranslatorJobClass:
-  case Action::ObjcopyJobClass:
     llvm_unreachable("Invalid tool kind.");
 
+  case Action::ObjcopyJobClass:
+    return nullptr;
+
   case Action::CompileJobClass:
   case Action::PrecompileJobClass:
   case Action::PreprocessJobClass:
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp 
b/clang/lib/Driver/ToolChains/MSVC.cpp
index 8141f9f132421..ba8fdb9060b5c 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -525,6 +525,17 @@ MSVCToolChain::MSVCToolChain(const Driver &D, const 
llvm::Triple &Triple,
       llvm::findVCToolChainViaRegistry(VCToolChainPath, VSLayout);
 }
 
+Tool *MSVCToolChain::getTool(Action::ActionClass AC) const {
+  switch (AC) {
+  case Action::ObjcopyJobClass:
+    if (!LLVMObjcopy)
+      LLVMObjcopy.reset(new tools::MinGW::LLVMObjcopy(*this));
+    return LLVMObjcopy.get();
+  default:
+    return ToolChain::getTool(AC);
+  }
+}
+
 Tool *MSVCToolChain::buildLinker() const {
   return new tools::visualstudio::Linker(*this);
 }
diff --git a/clang/lib/Driver/ToolChains/MSVC.h 
b/clang/lib/Driver/ToolChains/MSVC.h
index dcf4c0b488171..f231dd5824a6e 100644
--- a/clang/lib/Driver/ToolChains/MSVC.h
+++ b/clang/lib/Driver/ToolChains/MSVC.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_MSVC_H
 #define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_MSVC_H
 
+#include "MinGW.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/CudaInstallationDetector.h"
 #include "clang/Driver/LazyDetector.h"
@@ -137,8 +138,10 @@ class LLVM_LIBRARY_VISIBILITY MSVCToolChain : public 
ToolChain {
                                      const Twine &subfolder2 = "",
                                      const Twine &subfolder3 = "") const;
 
+  Tool *getTool(Action::ActionClass AC) const override;
   Tool *buildLinker() const override;
   Tool *buildAssembler() const override;
+
 private:
   std::optional<llvm::StringRef> WinSdkDir, WinSdkVersion, WinSysRoot;
   std::string VCToolChainPath;
@@ -146,6 +149,7 @@ class LLVM_LIBRARY_VISIBILITY MSVCToolChain : public 
ToolChain {
   LazyDetector<CudaInstallationDetector> CudaInstallation;
   LazyDetector<RocmInstallationDetector> RocmInstallation;
   LazyDetector<SYCLInstallationDetector> SYCLInstallation;
+  mutable std::unique_ptr<tools::MinGW::LLVMObjcopy> LLVMObjcopy;
 };
 
 } // end namespace toolchains
diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp 
b/clang/lib/Driver/ToolChains/MinGW.cpp
index e3f8cb8292fc8..f91b292f1037c 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -387,6 +387,31 @@ void tools::MinGW::Linker::ConstructJob(Compilation &C, 
const JobAction &JA,
                                          Exec, CmdArgs, Inputs, Output));
 }
 
+void tools::MinGW::LLVMObjcopy::ConstructJob(Compilation &C,
+                                             const JobAction &JA,
+                                             const InputInfo &Output,
+                                             const InputInfoList &Inputs,
+                                             const ArgList &Args,
+                                             const char *LinkingOutput) const {
+
+  std::string ObjcopyPath = getToolChain().GetProgramPath("llvm-objcopy");
+  const char *Exec = Args.MakeArgString(ObjcopyPath);
+
+  // Assume llvm-objcopy is only used for hybrid ARM64X object files.
+  assert(Inputs.size() == 2 && "Expected 2 inputs.");
+  // Embed the hybrid object in the .llvm.arm64x section.
+  ArgStringList CmdArgs;
+  CmdArgs.push_back(Args.MakeArgString("--add-section=.llvm.arm64x=" +
+                                       Twine(Inputs[0].getFilename())));
+  // Mark the .llvm.arm64x section as discardable.
+  CmdArgs.push_back("--set-section-flags=.llvm.arm64x=debug");
+  CmdArgs.push_back(Inputs[1].getFilename());
+  CmdArgs.push_back(Output.getFilename());
+
+  C.addCommand(std::make_unique<Command>(JA, *this, 
ResponseFileSupport::None(),
+                                         Exec, CmdArgs, Inputs, Output));
+}
+
 static bool isCrossCompiling(const llvm::Triple &T, bool RequireArchMatch) {
   llvm::Triple HostTriple(llvm::Triple::normalize(LLVM_HOST_TRIPLE));
   if (HostTriple.getOS() != llvm::Triple::Win32)
@@ -575,6 +600,10 @@ Tool *toolchains::MinGW::getTool(Action::ActionClass AC) 
const {
     if (!Compiler)
       Compiler.reset(new tools::gcc::Compiler(*this));
     return Compiler.get();
+  case Action::ObjcopyJobClass:
+    if (!LLVMObjcopy)
+      LLVMObjcopy.reset(new tools::MinGW::LLVMObjcopy(*this));
+    return LLVMObjcopy.get();
   default:
     return ToolChain::getTool(AC);
   }
diff --git a/clang/lib/Driver/ToolChains/MinGW.h 
b/clang/lib/Driver/ToolChains/MinGW.h
index ddf9dc500960b..8c54609afddaa 100644
--- a/clang/lib/Driver/ToolChains/MinGW.h
+++ b/clang/lib/Driver/ToolChains/MinGW.h
@@ -52,6 +52,19 @@ class LLVM_LIBRARY_VISIBILITY Linker final : public Tool {
   void AddLibGCC(const llvm::opt::ArgList &Args,
                  llvm::opt::ArgStringList &CmdArgs) const;
 };
+
+class LLVM_LIBRARY_VISIBILITY LLVMObjcopy : public Tool {
+public:
+  LLVMObjcopy(const ToolChain &TC)
+      : Tool("MinGW::LLVMObjcopy", "llvm-objcopy", TC) {}
+
+  bool hasIntegratedCPP() const override { return false; }
+
+  void ConstructJob(Compilation &C, const JobAction &JA,
+                    const InputInfo &Output, const InputInfoList &Inputs,
+                    const llvm::opt::ArgList &TCArgs,
+                    const char *LinkingOutput) const override;
+};
 } // end namespace MinGW
 } // end namespace tools
 
@@ -117,6 +130,7 @@ class LLVM_LIBRARY_VISIBILITY MinGW : public ToolChain {
   std::string TripleDirName;
   mutable std::unique_ptr<tools::gcc::Preprocessor> Preprocessor;
   mutable std::unique_ptr<tools::gcc::Compiler> Compiler;
+  mutable std::unique_ptr<tools::MinGW::LLVMObjcopy> LLVMObjcopy;
   void findGccLibDir(const llvm::Triple &LiteralTriple);
 
   bool NativeLLVMSupport;
diff --git a/clang/test/Driver/arm64x.c b/clang/test/Driver/arm64x.c
new file mode 100644
index 0000000000000..fc55703208187
--- /dev/null
+++ b/clang/test/Driver/arm64x.c
@@ -0,0 +1,6 @@
+// RUN: %clang -c -marm64x  --target=arm64ec-pc-windows-msvc -### %s 2>&1 | 
FileCheck %s
+// RUN: %clang -c -marm64x  --target=arm64ec-pc-windows-gnu -### %s 2>&1 | 
FileCheck %s
+
+// CHECK:      "-cc1" "-triple" "arm64ec-pc-windows-{{.*}}" "-emit-obj"
+// CHECK-NEXT: "-cc1" "-triple" "aarch64-pc-windows-{{.*}}" "-emit-obj"
+// CHECK-NEXT: llvm-objcopy" 
"--add-section=.llvm.arm64x={{.*}}arm64x-arm64ec-{{.*}}.o" 
"--set-section-flags=.llvm.arm64x=debug" "{{.*}}arm64x-aarch64-{{.*}}.o" 
"arm64x.o"
diff --git a/clang/test/Driver/msvc-link.c b/clang/test/Driver/msvc-link.c
index 5cb1653bf4db9..19027ff3e80ff 100644
--- a/clang/test/Driver/msvc-link.c
+++ b/clang/test/Driver/msvc-link.c
@@ -46,9 +46,9 @@
 // ARM64X: "-machine:arm64x"
 
 // RUN: not %clang --target=x86_64-linux-gnu -marm64x -### %s 2>&1 | FileCheck 
--check-prefix=HYBRID-ERR %s
-// HYBRID-ERR: error: unsupported option '-marm64x' for target 
'x86_64-linux-gnu'
+// HYBRID-ERR: error: unsupported option '-marm64x' for target 
'x86_64-unknown-linux-gnu'
 
-// RUN: %clang -c -marm64x  --target=arm64ec-pc-windows-msvc -fuse-ld=link 
-### %s 2>&1 | \
+// RUN: %clang -S -marm64x  --target=arm64ec-pc-windows-msvc -fuse-ld=link 
-### %s 2>&1 | \
 // RUN:        FileCheck --check-prefix=HYBRID-WARN %s
 // HYBRID-WARN: warning: argument unused during compilation: '-marm64x' 
[-Wunused-command-line-argument]
 

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