Boilerplate for producing XCOFF object files from the PowerPC backend.

[sfertile]

Summary

Stubs out a number of the classes needed to produce a new object file format (XCOFF) for the powerpc-aix target. For testing input is an empty module which produces an object file with just a file header.

[sfertile]

ping

[sfertile]

ping.

[sfertile]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1665

Just realized that this will change the AsmPrinter that will get created for triples like -mtriple=ppc32-- where no OS is specified. I'll fix this so Linux is still the default AsmPrinter.

[stefanp]

I'm not super familiar with the MC layer but overall this looks good to me.
I have a couple of minor comments.

Also, it seems that there is a part of that patch that is missing. The test added: aix-xcoff-basic.ll causes an assert with top of trunk.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.h

41

Why don't we pass in the is64Bit flag and the Triple into the function?
I know that we don't intend to support 64 bit from the start but I assume we will want to support it at one point right? We can check the flag at the start and if it is 64 bit we can emit a fatal_error or unreachable as you have done in other places.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp

91

So, previously the default was ELF now it is XCOFF.
This probably won't make much of a difference but ideally we should be spelling out what we support.

if (TheTriple.isOSDarwin())
  MAI = new PPCMCAsmInfoDarwin(isPPC64, TheTriple);
else if (TheTriple.isOSBinFormatELF())
   MAI = new PPCELFMCAsmInfo(isPPC64, TheTriple);
else if (TheTriple.isOSBinFormatXCOFF())
   MAI = new PPCXCOFFMCAsmInfo();
else
   llvm_unreachable("Unknown binary format.");

However, I don't know if the above is safe. Some code may rely on having ELF as default. Either way, I don't think we can leave it as XCOFF default.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h

55

Here too maybe we want to keep the 64 bit flag?

[hfinkel]

llvm/lib/MC/XCOFFObjectWriter.cpp

69

Will the tools on AIX complain if this is 0? Our general policy is that the compiler's output should be deterministic/reproducible and this breaks that. Looks like D23934 was never finished, but this value should be tied to that (once it's finished).

[sfertile]

llvm/lib/MC/XCOFFObjectWriter.cpp

69

No a zero value should be fine. Is the goal the compiler always produces reproducible output by default, or just that we can enable reproducible output with an option?

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h

55

Yeah, good idea. The first few patches for the Objectwriter are 32-bit only but we can simply report an error on 64-bit output for now.

[hfinkel]

llvm/lib/MC/XCOFFObjectWriter.cpp

69

Interesting question. I'd say by default, but I don't know that we've had a situation before where the platform default is to produce non-reproducible outputs at a low level (e.g., in the object-file format).

I recommend that we just set this to zero for now, and then have a separate discussion on how to change this later as necessary and/or desired.

[thakis]

llvm/lib/MC/XCOFFObjectWriter.cpp

69

If 0 works fine here, then go with that. But there's precedent for writing the current time into the output by default: clang-cl does that, since link.exe /incremental silently mislinks if that field is 0. So we do the safe thing by default and only write a 0 if the user explicitly passes /Brepro to clang-cl (which finally makes Asm.isIncrementalLinkerCompatible() return false here: http://llvm-cs.pcc.me.uk/lib/MC/WinCOFFObjectWriter.cpp#1057 )

[hubert.reinterpretcast]

llvm/include/llvm/MC/MCAsmInfoXCOFF.h

2

This is missing the - between the filename and the description.

llvm/include/llvm/MC/MCXCOFFStreamer.h

31

I don't think overriding a function just to call the direct base version of it is necessary.

llvm/include/llvm/Support/TargetRegistry.h

515

The use of the Register*Streamer functions is associated with registering the appropriate streamer factory function for the object file format given a specific architecture in lib/Target/*/MCTargetDesc. If there are no classes derived from MCXCOFFStreamer, then I don't think we need this.

llvm/lib/MC/MCAsmInfoXCOFF.cpp

2

Refer to the previous comment regarding a missing -.

llvm/lib/MC/MCXCOFFStreamer.cpp

31

If the intent is to fail with assertions but silently continue in release, then this should be
assert(false && "Not implemented yet");

Please review other uses of llvm_unreachable in this patch.

llvm/lib/MC/XCOFFObjectWriter.cpp

20

As a class defined in a .cpp file, this should probably go in an unnamed namespace.

24

The llvm:: here seems noisy and should be unnecessary here (and in a good number of cases in this file).

44

Does this need a TODO?

73

int32_t

75

uint16_t

77

uint16_t

llvm/lib/Target/PowerPC/MCTargetDesc/PPCXCOFFObjectWriter.cpp

21

Use // end anonymous namespace.

23

Use = default.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1651

Granted, this does not override a function just to clearly invoke the implementation in the direct base class, but explicitly skipping to an indirect base class with no comment is not better. Also, the direct base class does not override AsmPrinter::doFinalization anyway.

[sfertile]

Addressed review comments:

• Fixed up several comments
• removed overridden functions that only called based class implementation.
• fixed up logic for creating an MCAsmInfo and Streamers so that Linux/ELF remains the default.
• Removed code for registering an XCOFFStreamer creation callback as no classes extend the XCOFF streamer.
• reviewed usage of assert/llvm_unreachable. Converted most to report_fatal_error
• Always use a timestamp of '0' for reproducible. Fatal error if incremental linking is enabled.

Added MCSectionXCOFF class so we can create and switch to the .text section. This was implemented by Jason Liu, and it was in the branch I did the boilerplate work on, but wasn't up streamed itself as it was not testable on its own.

[sfertile]

llvm/lib/MC/MCXCOFFStreamer.cpp

31

I've updated to report_fatal_error so we get the same behavior in release and debug builds, but just realized I left the dead 'return' in. I'll fix this in the next update.

llvm/lib/MC/XCOFFObjectWriter.cpp

69

Docs claim 0 is fine and I had no issue in limited testing so I've changed to always using '0' for now. We can look at adding an option if needed when the toolchain is more usable on AIX.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp

91

Updated this and the Streamer creation to keep the defaults the same.

[hubert.reinterpretcast]

llvm/include/llvm/BinaryFormat/XCOFF.h

33

Missing close paren.

36

No period to be consistent with the other comments.

38

Uppercase "table" to be consistent with the other comments.

llvm/include/llvm/MC/MCContext.h

254

Why unsigned here, and XCOFF::StorageMappingClass elsewhere?

260

I suggest trying:

return std::tie(SectionName, MappingClass) <
       std::tie(Other.SectionName, Other.MappingClass);

llvm/include/llvm/MC/MCXCOFFObjectWriter.h

23

Use override.

25

Use override.

34

Most instances in the containing directory have a newline before the closing brace and "end namespace llvm".

[hubert.reinterpretcast]

llvm/lib/MC/MCSectionXCOFF.cpp

22

Is there a test for this?

llvm/lib/MC/XCOFFObjectWriter.cpp

26

The prevailing style in the containing directory is not to have both virtual and override on the same declaration. This comment applies to multiple instances in this file.

56

Typo: s/reporducibility/reproducibility/;

57

How is an XCOFF timestamp associated with "incremental linking" (apparently a feature of link.exe)?

86

No period after "namespace".

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp

86

s/is64Bit/Is64Bit/;

87

"Little-endian" with the hyphen.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp

245

"TOC entries are not supported yet."

249

Typos. Suggestion (if indeed the restriction is inherent):
"Invalid request to emit a machine pseudo-op for XCOFF."

llvm/lib/Target/PowerPC/MCTargetDesc/PPCXCOFFObjectWriter.cpp

20

Remove the period.

[sfertile]

Address review comments round 2.

- Various adjustments to various comments.
- Changed MappingClass in XCOFFSectionKey to use the enum type instead of unsigned.
- Removed 'virtual' from a declaration that is also marked 'override'.
- Add an Is64Bit fileld to the MCXCOFFObjectTargetWriter.
- Extended aix-xcoff-basic.ll to test switching to the '.text' section.
- Cleaned up comparison of XCOFFSectionKey by using std::tie.

[sfertile]

llvm/include/llvm/MC/MCContext.h

260

Good suggestion, thanks.

llvm/lib/MC/MCSectionXCOFF.cpp

22

There is now :)

llvm/lib/MC/XCOFFObjectWriter.cpp

57

IncrementalLinkerCompatible is a field in the generic MCAssembler and I don't see anything to indicate that its limited to Windows. The fact that toolchains that target 'Link.exe' are the only one to enabled it currently doesn't mean that won't change in the future. I'd rather be pedantic and show that there might be some compatibility issues between the behavior we have chosen for XCOFF and the MCAssembler behavior.

[hubert.reinterpretcast]

llvm/include/llvm/MC/MCXCOFFObjectWriter.h

40

} // end namespace llvm

llvm/lib/MC/MCXCOFFStreamer.cpp

31

Unreachable return false; still present.

llvm/lib/MC/XCOFFObjectWriter.cpp

57

The comment should put the concern into context. Something like "in case, like with Windows COFF, such a timestamp is incompatible with incremental linking of XCOFF".

[hubert.reinterpretcast]

llvm/lib/MC/MCObjectFileInfo.cpp

769

This choice of csect name is not a fundamental property of the object file format or of the ABI. A comment with suitable justification should be added.

I believe a good justification is that, on AIX, the __section__ attribute is not implemented by the IBM XL compiler, and the choice of using ".text" is compatible with GCC.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp

249

Suggestion (to avoid implying that there are valid machine pseudo-ops for XCOFF, should someone encounter the message): "Machine pseudo-ops are invalid for XCOFF."

253

Copy/paste error. Suggestion: "ABI-version pseudo-ops are invalid for XCOFF."

257

Copy/paste error. Suggestion: "Local-entry pseudo-ops are invalid for XCOFF."

llvm/test/CodeGen/PowerPC/aix-xcoff-basic.ll

8

The other RUN lines do not have < %s with two consecutive spaces.

32

I would prefer to have a comment to the effect that the csect need not be present, but we generate it anyway.

[hubert.reinterpretcast]

llvm/lib/MC/XCOFFObjectWriter.cpp

67

Typo: s/Finialize/Finalize/;

llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp

232

The starting indentation level does not match that of the preceding class.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

161

See previous comment about the starting indentation level.

llvm/test/CodeGen/PowerPC/aix-xcoff-basic.ll

32

Note that, at least in the current status of this patch, the assembly output and the object output from LLVM do not describe the same abstract XCOFF content.

[sfertile]

• Various comment tweaks and spelling fixes.
• Some indentation fixes and formatting changes.
• Removed unreachable return statement.
• Fixed error messages related to unsupported assembler pseudo ops.
• Added some comments to test clarifying why we are checking for .text csect, and that the binary and text outputs don't represent the same XCOFF content.

[hubert.reinterpretcast]

LGTM with minor comments.

llvm/lib/MC/MCObjectFileInfo.cpp

768

Minor nit: Add a comma after "[f]or example".

llvm/test/CodeGen/PowerPC/aix-xcoff-basic.ll

18

s/functionallity/functionality/;

36

s/llvm's defualt/LLVM's default/;

[stella.stamenova]

This broke the Windows LLDB bot: http://lab.llvm.org:8011/builders/lldb-x64-windows-ninja/builds/6493/steps/build/logs/stdio

[JamesNagurne]

Maybe someone can enlighten me as to why the build bots aren't tripping up on this one, but our group is running into this when we pull this commit from the upstream:

In MCStreamer.h, the declaration of the pure virtual EmitSymbolAttribute is:

virtual bool EmitSymbolAttribute(MCSymbol *Symbol,
                                 MCSymbolAttr AttrKind,
                                 StringRef AttrVal = StringRef()) = 0;

In this revision, in MCXCOFFStreamer.h, the declaration is:

bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;

This is ill-formed, because the 'override' declaration hides the pure virtual member function. Apparently the clang-fast build bots are ok with this, but I'm not sure how. A similar code segment (Compiler Explorer) fails on every clang compiler I've tried.

[sfertile]

In D61694#1576962, @JamesNagurne wrote:

Maybe someone can enlighten me as to why the build bots aren't tripping up on this one, but our group is running into this when we pull this commit from the upstream:

In MCStreamer.h, the declaration of the pure virtual EmitSymbolAttribute is:

virtual bool EmitSymbolAttribute(MCSymbol *Symbol,
                                 MCSymbolAttr AttrKind,
                                 StringRef AttrVal = StringRef()) = 0;

In this revision, in MCXCOFFStreamer.h, the declaration is:

bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;

This is ill-formed, because the 'override' declaration hides the pure virtual member function. Apparently the clang-fast build bots are ok with this, but I'm not sure how. A similar code segment (Compiler Explorer) fails on every clang compiler I've tried.

Have you modified the signature of EmitSymbolAttribute in your downstream repo? I see

/// Add the given \p Attribute to \p Symbol.
virtual bool EmitSymbolAttribute(MCSymbol *Symbol,
                                 MCSymbolAttr Attribute) = 0;

in trunk (line 492) and no one has modified the file for months. A change like this would land with no merge conflicts but still be semantically broken if you have modified the signature. FWIW it bootstraps on trunk at the time I landed it, (and I double checked again right now).

In D61694#1576922, @stella.stamenova wrote:

This broke the Windows LLDB bot: http://lab.llvm.org:8011/builders/lldb-x64-windows-ninja/builds/6493/steps/build/logs/stdio

Sorry about that, I believe @rnk landed a fix in https://reviews.llvm.org/rL365548, the buildbot turned green in the build that picked up that commit. Thanks Reid.

[JamesNagurne]

Oh dear... I apologize for that lapse of concentration. You are completely correct, someone had modified the signature in a prior commit, and I hadn't gone back far enough to see it.
Thank you for the response.

[sfertile]

np.

llvm/include/llvm/BinaryFormat/XCOFF.h

 
 namespace llvm {
 namespace XCOFF {
 
 // Constants used in the XCOFF definition.
 enum { SectionNameSize = 8, SymbolNameSize = 8 };
 enum ReservedSectionNum { N_DEBUG = -2, N_ABS = -1, N_UNDEF = 0 };
 
+// x_smclas field of x_csect from system header: /usr/include/syms.h
+/// Storage Mapping Class definitions.
+enum StorageMappingClass {
+  //     READ ONLY CLASSES
+  XMC_PR = 0,      ///< Program Code
+  XMC_RO = 1,      ///< Read Only Constant
+  XMC_DB = 2,      ///< Debug Dictionary Table
+  XMC_GL = 6,      ///< Global Linkage (Interfile Interface Code)
+  XMC_XO = 7,      ///< Extended Operation (Pseudo Machine Instruction
+  XMC_SV = 8,      ///< Supervisor Call (32-bit process only)
+  XMC_SV64 = 17,   ///< Supervisor Call for 64-bit process
+  XMC_SV3264 = 18, ///< Supervisor Call for both 32- and 64-bit processes.
+  XMC_TI = 12,     ///< Traceback Index csect
+  XMC_TB = 13,     ///< Traceback table csect
+
+  //       READ WRITE CLASSES
+  XMC_RW = 5,   ///< Read Write Data
+  XMC_TC0 = 15, ///< TOC Anchor for TOC Addressability
+  XMC_TC = 3,   ///< General TOC item
+  XMC_TD = 16,  ///< Scalar data item in the TOC
+  XMC_DS = 10,  ///< Descriptor csect
+  XMC_UA = 4,   ///< Unclassified - Treated as Read Write
+  XMC_BS = 9,   ///< BSS class (uninitialized static internal)
+  XMC_UC = 11,  ///< Un-named Fortran Common
+
+  XMC_TL = 20, ///< Initialized thread-local variable
+  XMC_UL = 21, ///< Uninitialized thread-local variable
+  XMC_TE = 22  ///< Symbol mapped at the end of TOC
+};
+
 // Flags for defining the section type. Used for the s_flags field of
 // the section header structure. Defined in the system header `scnhdr.h`.
 enum SectionTypeFlags {
   STYP_PAD = 0x0008,
   STYP_DWARF = 0x0010,
   STYP_TEXT = 0x0020,
   STYP_DATA = 0x0040,
   STYP_BSS = 0x0080,

llvm/include/llvm/MC/MCAsmInfoXCOFF.h

+//===- MCAsmInfoXCOFF.h - XCOFF asm properties ----------------- *- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCASMINFOXCOFF_H
+#define LLVM_MC_MCASMINFOXCOFF_H
+
+#include "llvm/MC/MCAsmInfo.h"
+
+namespace llvm {
+
+class MCAsmInfoXCOFF : public MCAsmInfo {
+  virtual void anchor();
+
+protected:
+  MCAsmInfoXCOFF();
+};
+
+} // end namespace llvm
+
+#endif // LLVM_MC_MCASMINFOXCOFF_H

llvm/include/llvm/MC/MCContext.h

 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/BinaryFormat/XCOFF.h"
 #include "llvm/MC/MCAsmMacro.h"
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/MD5.h"
namespace llvm {
   class MCLabel;
   class MCObjectFileInfo;
   class MCRegisterInfo;
   class MCSection;
   class MCSectionCOFF;
   class MCSectionELF;
   class MCSectionMachO;
   class MCSectionWasm;
+  class MCSectionXCOFF;
   class MCStreamer;
   class MCSymbol;
   class MCSymbolELF;
   class MCSymbolWasm;
   class SMLoc;
   class SourceMgr;
 
   /// Context object for machine code objects.  This class owns all of the
private:
     /// We use a bump pointer allocator to avoid the need to track all allocated
     /// objects.
     BumpPtrAllocator Allocator;
 
     SpecificBumpPtrAllocator<MCSectionCOFF> COFFAllocator;
     SpecificBumpPtrAllocator<MCSectionELF> ELFAllocator;
     SpecificBumpPtrAllocator<MCSectionMachO> MachOAllocator;
     SpecificBumpPtrAllocator<MCSectionWasm> WasmAllocator;
+    SpecificBumpPtrAllocator<MCSectionXCOFF> XCOFFAllocator;
 
     /// Bindings of names to symbols.
     SymbolTable Symbols;
 
     /// A mapping from a local label number and an instance count to a symbol.
     /// For example, in the assembly
     ///     1:
     ///     2:
struct WasmSectionKey {
         if (SectionName != Other.SectionName)
           return SectionName < Other.SectionName;
         if (GroupName != Other.GroupName)
           return GroupName < Other.GroupName;
         return UniqueID < Other.UniqueID;
       }
     };
 
+    struct XCOFFSectionKey {
+      std::string SectionName;
+      unsigned MappingClass;
+
+      XCOFFSectionKey(StringRef SectionName, unsigned MappingClass)
+          : SectionName(SectionName), MappingClass(MappingClass) {}
+
+      bool operator<(const XCOFFSectionKey &Other) const {
+        if (SectionName != Other.SectionName)
+          return SectionName < Other.SectionName;
+        return MappingClass < Other.MappingClass;
+      }
+    };
+
     StringMap<MCSectionMachO *> MachOUniquingMap;
     std::map<ELFSectionKey, MCSectionELF *> ELFUniquingMap;
     std::map<COFFSectionKey, MCSectionCOFF *> COFFUniquingMap;
     std::map<WasmSectionKey, MCSectionWasm *> WasmUniquingMap;
+    std::map<XCOFFSectionKey, MCSectionXCOFF *> XCOFFUniquingMap;
     StringMap<bool> RelSecNames;
 
     SpecificBumpPtrAllocator<MCSubtargetInfo> MCSubtargetAllocator;
 
     /// Do automatic reset in destructor
     bool AutoReset;
 
     bool HadError = false;
public:
     MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   const Twine &Group, unsigned UniqueID,
                                   const char *BeginSymName);
 
     MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   const MCSymbolWasm *Group, unsigned UniqueID,
                                   const char *BeginSymName);
 
+    MCSectionXCOFF *getXCOFFSection(StringRef Section,
+                                    XCOFF::StorageMappingClass MappingClass,
+                                    SectionKind K,
+                                    const char *BeginSymName = nullptr);
+
     // Create and save a copy of STI and return a reference to the copy.
     MCSubtargetInfo &getSubtargetCopy(const MCSubtargetInfo &STI);
 
     /// @}
 
     /// \name Dwarf Management
     /// @{
 

llvm/include/llvm/MC/MCObjectFileInfo.h

private:
   MCContext *Ctx;
   Triple TT;
   VersionTuple SDKVersion;
 
   void initMachOMCObjectFileInfo(const Triple &T);
   void initELFMCObjectFileInfo(const Triple &T, bool Large);
   void initCOFFMCObjectFileInfo(const Triple &T);
   void initWasmMCObjectFileInfo(const Triple &T);
+  void initXCOFFMCObjectFileInfo(const Triple &T);
   MCSection *getDwarfComdatSection(const char *Name, uint64_t Hash) const;
 
 public:
   const Triple &getTargetTriple() const { return TT; }
 
   void setSDKVersion(const VersionTuple &TheSDKVersion) {
     SDKVersion = TheSDKVersion;
   }
 
   const VersionTuple &getSDKVersion() const { return SDKVersion; }
 };
 
 } // end namespace llvm
 
 #endif

llvm/include/llvm/MC/MCSection.h

 template <> struct ilist_alloc_traits<MCFragment> {
   static void deleteNode(MCFragment *V);
 };
 
 /// Instances of this class represent a uniqued identifier for a section in the
 /// current translation unit.  The MCContext class uniques and creates these.
 class MCSection {
 public:
-  enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO, SV_Wasm };
+  enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO, SV_Wasm, SV_XCOFF };
 
   /// Express the state of bundle locked groups while emitting code.
   enum BundleLockStateType {
     NotBundleLocked,
     BundleLocked,
     BundleLockedAlignToEnd
   };
 

llvm/include/llvm/MC/MCSectionXCOFF.h

+//===- MCSectionXCOFF.h - XCOFF Machine Code Sections -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the MCSectionXCOFF class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCSECTIONXCOFF_H
+#define LLVM_MC_MCSECTIONXCOFF_H
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/BinaryFormat/XCOFF.h"
+#include "llvm/MC/MCSection.h"
+
+namespace llvm {
+
+class MCSymbol;
+
+// This class represents an XCOFF `Control Section`, more commonly referred to
+// as a csect. A csect represents the smallest possible unit of data/code which
+// will be relocated as a single block.
+class MCSectionXCOFF final : public MCSection {
+  friend class MCContext;
+
+  StringRef Name;
+  XCOFF::StorageMappingClass MappingClass;
+
+  MCSectionXCOFF(StringRef Section, XCOFF::StorageMappingClass SMC,
+                 SectionKind K, MCSymbol *Begin)
+      : MCSection(SV_XCOFF, K, Begin), Name(Section), MappingClass(SMC) {}
+
+public:
+  ~MCSectionXCOFF();
+
+  static bool classof(const MCSection *S) {
+    return S->getVariant() == SV_XCOFF;
+  }
+
+  StringRef getSectionName() const { return Name; }
+  XCOFF::StorageMappingClass getMappingClass() const { return MappingClass; }
+
+  void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
+                            raw_ostream &OS,
+                            const MCExpr *Subsection) const override;
+  bool UseCodeAlign() const override;
+  bool isVirtualSection() const override;
+};
+
+} // end namespace llvm
+
+#endif

llvm/include/llvm/MC/MCXCOFFObjectWriter.h

+//===-- llvm/MC/MCXCOFFObjectWriter.h - XCOFF Object Writer ---------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCXCOFFOBJECTWRITER_H
+#define LLVM_MC_MCXCOFFOBJECTWRITER_H
+
+#include "llvm/MC/MCObjectWriter.h"
+
+namespace llvm {
+
+class raw_pwrite_stream;
+
+class MCXCOFFObjectTargetWriter : public MCObjectTargetWriter {
+protected:
+  MCXCOFFObjectTargetWriter();
+
+public:
+  virtual ~MCXCOFFObjectTargetWriter();
+
+  virtual Triple::ObjectFormatType getFormat() const { return Triple::XCOFF; }
+  static bool classof(const MCObjectTargetWriter *W) {
+    return W->getFormat() == Triple::XCOFF;
+  }
+};
+
+std::unique_ptr<MCObjectWriter>
+createXCOFFObjectWriter(std::unique_ptr<MCXCOFFObjectTargetWriter> MOTW,
+                        raw_pwrite_stream &OS);
+} // namespace llvm
+
+#endif // LLVM_MC_MCXCOFFOBJECTWRITER_H

llvm/include/llvm/MC/MCXCOFFStreamer.h

+//===- MCXCOFFObjectStreamer.h - MCStreamer XCOFF Object File Interface ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCXCOFFSTREAMER_H
+#define LLVM_MC_MCXCOFFSTREAMER_H
+
+#include "llvm/MC/MCObjectStreamer.h"
+
+namespace llvm {
+
+class MCXCOFFStreamer : public MCObjectStreamer {
+public:
+  MCXCOFFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
+                  std::unique_ptr<MCObjectWriter> OW,
+                  std::unique_ptr<MCCodeEmitter> Emitter);
+
+  bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
+  void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                        unsigned ByteAlignment) override;
+  void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
+                    uint64_t Size = 0, unsigned ByteAlignment = 0,
+                    SMLoc Loc = SMLoc()) override;
+  void EmitInstToData(const MCInst &Inst, const MCSubtargetInfo &) override;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_MC_MCXCOFFSTREAMER_H

llvm/include/llvm/Support/TargetRegistry.h

MCStreamer *createMachOStreamer(MCContext &Ctx,
                                 std::unique_ptr<MCCodeEmitter> &&CE,
                                 bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                 bool LabelSections = false);
 MCStreamer *createWasmStreamer(MCContext &Ctx,
                                std::unique_ptr<MCAsmBackend> &&TAB,
                                std::unique_ptr<MCObjectWriter> &&OW,
                                std::unique_ptr<MCCodeEmitter> &&CE,
                                bool RelaxAll);
+MCStreamer *createXCOFFStreamer(MCContext &Ctx,
+                                std::unique_ptr<MCAsmBackend> &&TAB,
+                                std::unique_ptr<MCObjectWriter> &&OW,
+                                std::unique_ptr<MCCodeEmitter> &&CE,
+                                bool RelaxAll);
 
 MCRelocationInfo *createMCRelocationInfo(const Triple &TT, MCContext &Ctx);
 
 MCSymbolizer *createMCSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo,
                                  LLVMSymbolLookupCallback SymbolLookUp,
                                  void *DisInfo, MCContext *Ctx,
                                  std::unique_ptr<MCRelocationInfo> &&RelInfo);
 
using COFFStreamerCtorTy =
                       std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll,
                       bool IncrementalLinkerCompatible);
   using WasmStreamerCtorTy =
       MCStreamer *(*)(const Triple &T, MCContext &Ctx,
                       std::unique_ptr<MCAsmBackend> &&TAB,
                       std::unique_ptr<MCObjectWriter> &&OW,
                       std::unique_ptr<MCCodeEmitter> &&Emitter, bool RelaxAll);
+
   using NullTargetStreamerCtorTy = MCTargetStreamer *(*)(MCStreamer &S);
   using AsmTargetStreamerCtorTy = MCTargetStreamer *(*)(
       MCStreamer &S, formatted_raw_ostream &OS, MCInstPrinter *InstPrint,
       bool IsVerboseAsm);
   using ObjectTargetStreamerCtorTy = MCTargetStreamer *(*)(
       MCStreamer &S, const MCSubtargetInfo &STI);
   using MCRelocationInfoCtorTy = MCRelocationInfo *(*)(const Triple &TT,
                                                        MCContext &Ctx);
MCStreamer *createMCObjectStreamer(const Triple &T, MCContext &Ctx,
     case Triple::Wasm:
       if (WasmStreamerCtorFn)
         S = WasmStreamerCtorFn(T, Ctx, std::move(TAB), std::move(OW),
                                std::move(Emitter), RelaxAll);
       else
         S = createWasmStreamer(Ctx, std::move(TAB), std::move(OW),
                                std::move(Emitter), RelaxAll);
       break;
+    case Triple::XCOFF:
+        S = createXCOFFStreamer(Ctx, std::move(TAB), std::move(OW),
+                                std::move(Emitter), RelaxAll);
+      break;
     }
     if (ObjectTargetStreamerCtorFn)
       ObjectTargetStreamerCtorFn(*S, STI);
     return S;
   }
 
   MCStreamer *createAsmStreamer(MCContext &Ctx,
                                 std::unique_ptr<formatted_raw_ostream> OS,

llvm/lib/MC/CMakeLists.txt

 add_llvm_library(LLVMMC
   ConstantPools.cpp
   ELFObjectWriter.cpp
   MCAsmBackend.cpp
   MCAsmInfo.cpp
   MCAsmInfoCOFF.cpp
   MCAsmInfoDarwin.cpp
   MCAsmInfoELF.cpp
   MCAsmInfoWasm.cpp
+  MCAsmInfoXCOFF.cpp
   MCAsmMacro.cpp
   MCAsmStreamer.cpp
   MCAssembler.cpp
   MCCodeEmitter.cpp
   MCCodePadder.cpp
   MCCodeView.cpp
   MCContext.cpp
   MCDwarf.cpp
add_llvm_library(LLVMMC
   MCObjectWriter.cpp
   MCRegisterInfo.cpp
   MCSchedule.cpp
   MCSection.cpp
   MCSectionCOFF.cpp
   MCSectionELF.cpp
   MCSectionMachO.cpp
   MCSectionWasm.cpp
+  MCSectionXCOFF.cpp
   MCStreamer.cpp
   MCSubtargetInfo.cpp
   MCSymbol.cpp
   MCSymbolELF.cpp
   MCTargetOptions.cpp
   MCValue.cpp
   MCWasmObjectTargetWriter.cpp
   MCWasmStreamer.cpp
   MCWin64EH.cpp
   MCWinCOFFStreamer.cpp
   MCWinEH.cpp
+  MCXCOFFObjectTargetWriter.cpp
+  MCXCOFFStreamer.cpp
   MachObjectWriter.cpp
   StringTableBuilder.cpp
   SubtargetFeature.cpp
   WasmObjectWriter.cpp
   WinCOFFObjectWriter.cpp
+  XCOFFObjectWriter.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/MC
   )
 
 add_subdirectory(MCParser)
 add_subdirectory(MCDisassembler)

llvm/lib/MC/MCAsmBackend.cpp

 #include "llvm/ADT/STLExtras.h"
 #include "llvm/MC/MCCodePadder.h"
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCMachObjectWriter.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCWasmObjectWriter.h"
 #include "llvm/MC/MCWinCOFFObjectWriter.h"
+#include "llvm/MC/MCXCOFFObjectWriter.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 
 using namespace llvm;
 
 MCAsmBackend::MCAsmBackend(support::endianness Endian)
     : CodePadder(new MCCodePadder()), Endian(Endian) {}
case Triple::MachO:
     return createMachObjectWriter(cast<MCMachObjectTargetWriter>(std::move(TW)),
                                   OS, Endian == support::little);
   case Triple::COFF:
     return createWinCOFFObjectWriter(
         cast<MCWinCOFFObjectTargetWriter>(std::move(TW)), OS);
   case Triple::Wasm:
     return createWasmObjectWriter(cast<MCWasmObjectTargetWriter>(std::move(TW)),
                                   OS);
+  case Triple::XCOFF:
+    return createXCOFFObjectWriter(
+        cast<MCXCOFFObjectTargetWriter>(std::move(TW)), OS);
   default:
     llvm_unreachable("unexpected object format");
   }
 }
 
 std::unique_ptr<MCObjectWriter>
 MCAsmBackend::createDwoObjectWriter(raw_pwrite_stream &OS,
                                     raw_pwrite_stream &DwoOS) const {

llvm/lib/MC/MCAsmInfoXCOFF.cpp

+//===- MC/MCAsmInfoXCOFF.cpp - XCOFF asm properties ------------ *- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCAsmInfoXCOFF.h"
+
+using namespace llvm;
+
+void MCAsmInfoXCOFF::anchor() {}
+
+MCAsmInfoXCOFF::MCAsmInfoXCOFF() {
+  IsLittleEndian = false;
+  HasDotTypeDotSizeDirective = false;
+}

llvm/lib/MC/MCContext.cpp

 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFragment.h"
 #include "llvm/MC/MCLabel.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSectionXCOFF.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCSymbolCOFF.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCSymbolMachO.h"
 #include "llvm/MC/MCSymbolWasm.h"
 #include "llvm/MC/MCSymbolXCOFF.h"
 #include "llvm/MC/SectionKind.h"

 // Module Lifetime Management
 //===----------------------------------------------------------------------===//
 
 void MCContext::reset() {
   // Call the destructors so the fragments are freed
   COFFAllocator.DestroyAll();
   ELFAllocator.DestroyAll();
   MachOAllocator.DestroyAll();
+  XCOFFAllocator.DestroyAll();
 
   MCSubtargetAllocator.DestroyAll();
   UsedNames.clear();
   Symbols.clear();
   Allocator.Reset();
   Instances.clear();
   CompilationDir.clear();
   MainFileName.clear();
   MCDwarfLineTablesCUMap.clear();
   SectionsForRanges.clear();
   MCGenDwarfLabelEntries.clear();
   DwarfDebugFlags = StringRef();
   DwarfCompileUnitID = 0;
   CurrentDwarfLoc = MCDwarfLoc(0, 0, 0, DWARF2_FLAG_IS_STMT, 0, 0);
 
   CVContext.reset();
 
   MachOUniquingMap.clear();
   ELFUniquingMap.clear();
   COFFUniquingMap.clear();
   WasmUniquingMap.clear();
+  XCOFFUniquingMap.clear();
 
   NextID.clear();
   AllowTemporaryLabels = true;
   DwarfLocSeen = false;
   GenDwarfForAssembly = false;
   GenDwarfFileNumber = 0;
 
   HadError = false;
MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
   auto *F = new MCDataFragment();
   Result->getFragmentList().insert(Result->begin(), F);
   F->setParent(Result);
   Begin->setFragment(F);
 
   return Result;
 }
 
+MCSectionXCOFF *MCContext::getXCOFFSection(StringRef Section,
+                                           XCOFF::StorageMappingClass SMC,
+                                           SectionKind Kind,
+                                           const char *BeginSymName) {
+  // Do the lookup. If we have a hit, return it.
+  auto IterBool = XCOFFUniquingMap.insert(
+      std::make_pair(XCOFFSectionKey{Section.str(), SMC}, nullptr));
+  auto &Entry = *IterBool.first;
+  if (!IterBool.second)
+    return Entry.second;
+
+  // Otherwise, return a new section.
+  StringRef CachedName = Entry.first.SectionName;
+
+  MCSymbol *Begin = nullptr;
+  if (BeginSymName)
+    Begin = createTempSymbol(BeginSymName, false);
+
+  MCSectionXCOFF *Result = new (XCOFFAllocator.Allocate())
+      MCSectionXCOFF(CachedName, SMC, Kind, Begin);
+  Entry.second = Result;
+
+  auto *F = new MCDataFragment();
+  Result->getFragmentList().insert(Result->begin(), F);
+  F->setParent(Result);
+
+  if (Begin)
+    Begin->setFragment(F);
+
+  return Result;
+}
+
 MCSubtargetInfo &MCContext::getSubtargetCopy(const MCSubtargetInfo &STI) {
   return *new (MCSubtargetAllocator.Allocate()) MCSubtargetInfo(STI);
 }
 
 void MCContext::addDebugPrefixMapEntry(const std::string &From,
                                        const std::string &To) {
   DebugPrefixMap.insert(std::make_pair(From, To));
 }

llvm/lib/MC/MCObjectFileInfo.cpp

 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSectionXCOFF.h"
 
 using namespace llvm;
 
 static bool useCompactUnwind(const Triple &T) {
   // Only on darwin.
   if (!T.isOSDarwin())
     return false;
 
void MCObjectFileInfo::initWasmMCObjectFileInfo(const Triple &T) {
   // TODO Consider putting each function's exception table in a separate
   // section, as in -function-sections, to facilitate lld's --gc-section.
   LSDASection = Ctx->getWasmSection(".rodata.gcc_except_table",
                                     SectionKind::getReadOnlyWithRel());
 
   // TODO: Define more sections.
 }
 
+void MCObjectFileInfo::initXCOFFMCObjectFileInfo(const Triple &T) {
+  // The default csect for program code. Functions without a specified section
+  // get placed into this csect.
+  TextSection = Ctx->getXCOFFSection(
+      ".text", XCOFF::StorageMappingClass::XMC_PR, SectionKind::getText());
+}
+
 void MCObjectFileInfo::InitMCObjectFileInfo(const Triple &TheTriple, bool PIC,
                                             MCContext &ctx,
                                             bool LargeCodeModel) {
   PositionIndependent = PIC;
   Ctx = &ctx;
 
   // Common.
   CommDirectiveSupportsAlignment = true;
case Triple::ELF:
     initELFMCObjectFileInfo(TT, LargeCodeModel);
     break;
   case Triple::Wasm:
     Env = IsWasm;
     initWasmMCObjectFileInfo(TT);
     break;
   case Triple::XCOFF:
     Env = IsXCOFF;
-    // TODO: Initialize MCObjectFileInfo for XCOFF format when
-    // MCSectionXCOFF is ready.
+    initXCOFFMCObjectFileInfo(TT);
     break;
   case Triple::UnknownObjectFormat:
     report_fatal_error("Cannot initialize MC for unknown object file format.");
     break;
   }
 }
 
 MCSection *MCObjectFileInfo::getDwarfComdatSection(const char *Name,

llvm/lib/MC/MCSectionXCOFF.cpp

+//===- lib/MC/MCSectionXCOFF.cpp - XCOFF Code Section Representation ------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCSectionXCOFF.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+MCSectionXCOFF::~MCSectionXCOFF() = default;
+
+void MCSectionXCOFF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
+                                          raw_ostream &OS,
+                                          const MCExpr *Subsection) const {
+  if (getKind().isText()) {
+    OS << "\t.csect " << getSectionName() << "["
+       << "PR"
+       << "]" << '\n';
+    return;
+  }
+
+  report_fatal_error("Printing for this SectionKind is unimplemented.");
+}
+
+bool MCSectionXCOFF::UseCodeAlign() const { return getKind().isText(); }
+
+bool MCSectionXCOFF::isVirtualSection() const { return !getKind().isCommon(); }

llvm/lib/MC/MCXCOFFObjectTargetWriter.cpp

+//===- MCXCOFFObjectTargetWriter.cpp - XCOFF Target Writer Subclass -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCXCOFFObjectWriter.h"
+
+using namespace llvm;
+
+MCXCOFFObjectTargetWriter::MCXCOFFObjectTargetWriter() = default;
+MCXCOFFObjectTargetWriter::~MCXCOFFObjectTargetWriter() = default;

llvm/lib/MC/MCXCOFFStreamer.cpp

+//===- lib/MC/MCXCOFFStreamer.cpp - XCOFF Object Output -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file assembles .s files and emits XCOFF .o object files.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCXCOFFStreamer.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/Support/TargetRegistry.h"
+
+using namespace llvm;
+
+MCXCOFFStreamer::MCXCOFFStreamer(MCContext &Context,
+                                 std::unique_ptr<MCAsmBackend> MAB,
+                                 std::unique_ptr<MCObjectWriter> OW,
+                                 std::unique_ptr<MCCodeEmitter> Emitter)
+    : MCObjectStreamer(Context, std::move(MAB), std::move(OW),
+                       std::move(Emitter)) {}
+
+bool MCXCOFFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
+                                          MCSymbolAttr Attribute) {
+  report_fatal_error("Symbol attributes not implemented for XCOFF.");
+  return false;
+}
+
+void MCXCOFFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                       unsigned ByteAlignment) {
+  report_fatal_error("Emiting common symbols not implemented for XCOFF.");
+}
+
+void MCXCOFFStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
+                                   uint64_t Size, unsigned ByteAlignment,
+                                   SMLoc Loc) {
+  report_fatal_error("Zero fill not implemented for XCOFF.");
+}
+
+void MCXCOFFStreamer::EmitInstToData(const MCInst &Inst,
+                                     const MCSubtargetInfo &) {
+  report_fatal_error("Instruction emission not implemented for XCOFF.");
+}
+
+MCStreamer *llvm::createXCOFFStreamer(MCContext &Context,
+                                      std::unique_ptr<MCAsmBackend> &&MAB,
+                                      std::unique_ptr<MCObjectWriter> &&OW,
+                                      std::unique_ptr<MCCodeEmitter> &&CE,
+                                      bool RelaxAll) {
+  MCXCOFFStreamer *S = new MCXCOFFStreamer(Context, std::move(MAB),
+                                           std::move(OW), std::move(CE));
+  if (RelaxAll)
+    S->getAssembler().setRelaxAll(true);
+  return S;
+}

llvm/lib/MC/XCOFFObjectWriter.cpp

+//===-- lib/MC/XCOFFObjectWriter.cpp - XCOFF file writer ------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements XCOFF object file writer information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/MCXCOFFObjectWriter.h"
+
+using namespace llvm;
+
+namespace {
+
+class XCOFFObjectWriter : public MCObjectWriter {
+  support::endian::Writer W;
+  std::unique_ptr<MCXCOFFObjectTargetWriter> TargetObjectWriter;
+
+  virtual void executePostLayoutBinding(MCAssembler &,
+                                        const MCAsmLayout &) override;
+
+  virtual void recordRelocation(MCAssembler &, const MCAsmLayout &,
+                                const MCFragment *, const MCFixup &, MCValue,
+                                uint64_t &) override;
+
+  virtual uint64_t writeObject(MCAssembler &, const MCAsmLayout &) override;
+
+public:
+  XCOFFObjectWriter(std::unique_ptr<MCXCOFFObjectTargetWriter> MOTW,
+                    raw_pwrite_stream &OS);
+};
+
+XCOFFObjectWriter::XCOFFObjectWriter(
+    std::unique_ptr<MCXCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS)
+    : W(OS, support::big), TargetObjectWriter(std::move(MOTW)) {}
+
+void XCOFFObjectWriter::executePostLayoutBinding(MCAssembler &,
+                                                 const MCAsmLayout &) {
+  // TODO Implement once we have sections and symbols to handle.
+}
+
+void XCOFFObjectWriter::recordRelocation(MCAssembler &, const MCAsmLayout &,
+                                         const MCFragment *, const MCFixup &,
+                                         MCValue, uint64_t &) {
+  report_fatal_error("XCOFF relocations not supported.");
+}
+
+uint64_t XCOFFObjectWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &) {
+  // We always emit a timestamp of 0 for reporducibility, so ensure incremental
+  // linking is not enabled.
+  if (Asm.isIncrementalLinkerCompatible())
+    report_fatal_error("Incremental linking not supported for XCOFF.");
+
+  uint64_t StartOffset = W.OS.tell();
+
+  // TODO FIXME Assign section numbers/finalize sections.
+
+  // TODO FIXME Finialize symbols.
+
+  // Magic.
+  W.write<uint16_t>(0x01df);
+  // Number of sections.
+  W.write<uint16_t>(0);
+  // Timestamp field. For reproducible output we write a 0, which represents no
+  // timestamp.
+  W.write<int32_t>(0);
+  // Byte Offset to the start of the symbol table.
+  W.write<uint32_t>(0);
+  // Number of entries in the symbol table.
+  W.write<int32_t>(0);
+  // Size of the optional header.
+  W.write<uint16_t>(0);
+  // Flags.
+  W.write<uint16_t>(0);
+
+  return W.OS.tell() - StartOffset;
+}
+
+} // end anonymous namespace.
+
+std::unique_ptr<MCObjectWriter>
+llvm::createXCOFFObjectWriter(std::unique_ptr<MCXCOFFObjectTargetWriter> MOTW,
+                              raw_pwrite_stream &OS) {
+  return make_unique<XCOFFObjectWriter>(std::move(MOTW), OS);
+}

llvm/lib/Target/PowerPC/MCTargetDesc/CMakeLists.txt

 add_llvm_library(LLVMPowerPCDesc
   PPCAsmBackend.cpp
   PPCInstPrinter.cpp
   PPCMCTargetDesc.cpp
   PPCMCAsmInfo.cpp
   PPCMCCodeEmitter.cpp
   PPCMCExpr.cpp
   PPCPredicates.cpp
   PPCMachObjectWriter.cpp
   PPCELFObjectWriter.cpp
+  PPCXCOFFObjectWriter.cpp
   )

llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp

createObjectTargetWriter() const override {
     uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
     bool Is64 = TT.isPPC64();
     return createPPCELFObjectWriter(Is64, OSABI);
   }
 
   Optional<MCFixupKind> getFixupKind(StringRef Name) const override;
 };
 
+  class XCOFFPPCAsmBackend : public PPCAsmBackend {
+  public:
+    XCOFFPPCAsmBackend(const Target &T, const Triple &TT)
+        : PPCAsmBackend(T, TT) {}
+
+    std::unique_ptr<MCObjectTargetWriter>
+    createObjectTargetWriter() const override {
+      if (TT.isArch64Bit())
+        report_fatal_error("64-bit XCOFF object files are not supported yet.");
+
+      return createPPCXCOFFObjectWriter(TT.isArch64Bit());
+    }
+  };
+
 } // end anonymous namespace
 
 Optional<MCFixupKind> ELFPPCAsmBackend::getFixupKind(StringRef Name) const {
   if (TT.isPPC64()) {
     if (Name == "R_PPC64_NONE")
       return FK_NONE;
   } else {
     if (Name == "R_PPC_NONE")
       return FK_NONE;
   }
   return MCAsmBackend::getFixupKind(Name);
 }
 
 MCAsmBackend *llvm::createPPCAsmBackend(const Target &T,
                                         const MCSubtargetInfo &STI,
                                         const MCRegisterInfo &MRI,
                                         const MCTargetOptions &Options) {
   const Triple &TT = STI.getTargetTriple();
   if (TT.isOSDarwin())
     return new DarwinPPCAsmBackend(T, TT);
 
+  if (TT.isOSBinFormatXCOFF())
+    return new XCOFFPPCAsmBackend(T, TT);
+
   return new ELFPPCAsmBackend(T, TT);
 }

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.h

 //===-- PPCMCAsmInfo.h - PPC asm properties --------------------*- C++ -*--===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
-// This file contains the declaration of the MCAsmInfoDarwin class.
+// This file contains the declarations of the PowerPC MCAsmInfo classes.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_POWERPC_MCTARGETDESC_PPCMCASMINFO_H
 #define LLVM_LIB_TARGET_POWERPC_MCTARGETDESC_PPCMCASMINFO_H
 
 #include "llvm/MC/MCAsmInfoDarwin.h"
 #include "llvm/MC/MCAsmInfoELF.h"
+#include "llvm/MC/MCAsmInfoXCOFF.h"
 
 namespace llvm {
 class Triple;
 
 class PPCMCAsmInfoDarwin : public MCAsmInfoDarwin {
   virtual void anchor();
 
 public:
   explicit PPCMCAsmInfoDarwin(bool is64Bit, const Triple &);
 };
 
 class PPCELFMCAsmInfo : public MCAsmInfoELF {
   void anchor() override;
 
 public:
   explicit PPCELFMCAsmInfo(bool is64Bit, const Triple &);
 };
 
+class PPCXCOFFMCAsmInfo : public MCAsmInfoXCOFF {
+  virtual void anchor();
+
+public:
+  explicit PPCXCOFFMCAsmInfo(bool is64Bit, const Triple &);
+};
+
 } // namespace llvm
 
 #endif

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp

PPCELFMCAsmInfo::PPCELFMCAsmInfo(bool is64Bit, const Triple& T) {
   ZeroDirective = "\t.space\t";
   Data64bitsDirective = is64Bit ? "\t.quad\t" : nullptr;
   AssemblerDialect = 1;           // New-Style mnemonics.
   LCOMMDirectiveAlignmentType = LCOMM::ByteAlignment;
 
   UseIntegratedAssembler = true;
 }
 
+void PPCXCOFFMCAsmInfo::anchor() {}
+
+PPCXCOFFMCAsmInfo::PPCXCOFFMCAsmInfo(bool is64Bit, const Triple &T) {
+  assert(!IsLittleEndian && "Little endian XCOFF not supported.");
+  CodePointerSize = CalleeSaveStackSlotSize = is64Bit ? 8 : 4;
+}

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h

 
 /// Construct an PPC ELF object writer.
 std::unique_ptr<MCObjectTargetWriter> createPPCELFObjectWriter(bool Is64Bit,
                                                                uint8_t OSABI);
 /// Construct a PPC Mach-O object writer.
 std::unique_ptr<MCObjectTargetWriter>
 createPPCMachObjectWriter(bool Is64Bit, uint32_t CPUType, uint32_t CPUSubtype);
 
+/// Construct a PPC XCOFF object writer.
+std::unique_ptr<MCObjectTargetWriter> createPPCXCOFFObjectWriter(bool Is64Bit);
+
 /// Returns true iff Val consists of one contiguous run of 1s with any number of
 /// 0s on either side.  The 1s are allowed to wrap from LSB to MSB, so
 /// 0x000FFF0, 0x0000FFFF, and 0xFF0000FF are all runs.  0x0F0F0000 is not,
 /// since all 1s are not contiguous.
 static inline bool isRunOfOnes(unsigned Val, unsigned &MB, unsigned &ME) {
   if (!Val)
     return false;
 

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp

 static MCAsmInfo *createPPCMCAsmInfo(const MCRegisterInfo &MRI,
                                      const Triple &TheTriple) {
   bool isPPC64 = (TheTriple.getArch() == Triple::ppc64 ||
                   TheTriple.getArch() == Triple::ppc64le);
 
   MCAsmInfo *MAI;
   if (TheTriple.isOSDarwin())
     MAI = new PPCMCAsmInfoDarwin(isPPC64, TheTriple);
+  else if (TheTriple.isOSBinFormatXCOFF())
+    MAI = new PPCXCOFFMCAsmInfo(isPPC64, TheTriple);
   else
     MAI = new PPCELFMCAsmInfo(isPPC64, TheTriple);
 
   // Initial state of the frame pointer is R1.
   unsigned Reg = isPPC64 ? PPC::X1 : PPC::R1;
   MCCFIInstruction Inst =
       MCCFIInstruction::createDefCfa(nullptr, MRI.getDwarfRegNum(Reg, true), 0);
   MAI->addInitialFrameState(Inst);
 
   return MAI;
 }
 
void emitAbiVersion(int AbiVersion) override {
     llvm_unreachable("Unknown pseudo-op: .abiversion");
   }
 
   void emitLocalEntry(MCSymbolELF *S, const MCExpr *LocalOffset) override {
     llvm_unreachable("Unknown pseudo-op: .localentry");
   }
 };
 
+class PPCTargetXCOFFStreamer : public PPCTargetStreamer {
+public:
+  PPCTargetXCOFFStreamer(MCStreamer &S) : PPCTargetStreamer(S) {}
+
+  void emitTCEntry(const MCSymbol &S) override {
+    report_fatal_error("TOC entry not supported yet.");
+  }
+
+  void emitMachine(StringRef CPU) override {
+    llvm_unreachable("emit machine pseduo-op no tsupported on XCOFF.");
+  }
+
+  void emitAbiVersion(int AbiVersion) override {
+    llvm_unreachable("Unknown pseudo-op: .abiversion");
+  }
+
+  void emitLocalEntry(MCSymbolELF *S, const MCExpr *LocalOffset) override {
+    llvm_unreachable("Unknown pseudo-op: .localentry");
+  }
+};
+
 } // end anonymous namespace
 
 static MCTargetStreamer *createAsmTargetStreamer(MCStreamer &S,
                                                  formatted_raw_ostream &OS,
                                                  MCInstPrinter *InstPrint,
                                                  bool isVerboseAsm) {
   return new PPCTargetAsmStreamer(S, OS);
 }
 
 static MCTargetStreamer *
 createObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
   const Triple &TT = STI.getTargetTriple();
   if (TT.isOSBinFormatELF())
     return new PPCTargetELFStreamer(S);
+  if (TT.isOSBinFormatXCOFF())
+    return new PPCTargetXCOFFStreamer(S);
   return new PPCTargetMachOStreamer(S);
 }
 
 static MCInstPrinter *createPPCMCInstPrinter(const Triple &T,
                                              unsigned SyntaxVariant,
                                              const MCAsmInfo &MAI,
                                              const MCInstrInfo &MII,
                                              const MCRegisterInfo &MRI) {

llvm/lib/Target/PowerPC/MCTargetDesc/PPCXCOFFObjectWriter.cpp

+//===-- PPCXCOFFObjectWriter.cpp - PowerPC XCOFF Writer -------------------===//
+//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "PPCMCTargetDesc.h"
+#include "llvm/MC/MCXCOFFObjectWriter.h"
+
+using namespace llvm;
+
+namespace {
+class PPCXCOFFObjectWriter : public MCXCOFFObjectTargetWriter {
+public:
+  PPCXCOFFObjectWriter();
+};
+} // end anonymous namespace.
+
+PPCXCOFFObjectWriter::PPCXCOFFObjectWriter() = default;
+
+std::unique_ptr<MCObjectTargetWriter>
+llvm::createPPCXCOFFObjectWriter(bool Is64Bit) {
+  if (Is64Bit)
+    report_fatal_error("64-bit XCOFF object support not implemented yet.");
+
+  return llvm::make_unique<PPCXCOFFObjectWriter>();
+}

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

public:
   StringRef getPassName() const override {
     return "Darwin PPC Assembly Printer";
   }
 
   bool doFinalization(Module &M) override;
   void EmitStartOfAsmFile(Module &M) override;
 };
 
+  class PPCAIXAsmPrinter : public PPCAsmPrinter {
+  public:
+    PPCAIXAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
+        : PPCAsmPrinter(TM, std::move(Streamer)) {}
+
+    StringRef getPassName() const override {
+      return "AIX PPC Assembly Printer";
+    }
+  };
+
 } // end anonymous namespace
 
 void PPCAsmPrinter::PrintSymbolOperand(const MachineOperand &MO,
                                        raw_ostream &O) {
   // Computing the address of a global symbol, not calling it.
   const GlobalValue *GV = MO.getGlobal();
   MCSymbol *SymToPrint;
 
bool PPCDarwinAsmPrinter::doFinalization(Module &M) {
   // implementation of multiple entry points).  If this doesn't occur, the
   // linker can safely perform dead code stripping.  Since LLVM never generates
   // code that does this, it is always safe to set.
   OutStreamer->EmitAssemblerFlag(MCAF_SubsectionsViaSymbols);
 
   return AsmPrinter::doFinalization(M);
 }
 
 /// createPPCAsmPrinterPass - Returns a pass that prints the PPC assembly code
 /// for a MachineFunction to the given output stream, in a format that the
 /// Darwin assembler can deal with.
 ///
 static AsmPrinter *
 createPPCAsmPrinterPass(TargetMachine &tm,
                         std::unique_ptr<MCStreamer> &&Streamer) {
   if (tm.getTargetTriple().isMacOSX())
     return new PPCDarwinAsmPrinter(tm, std::move(Streamer));
+  if (tm.getTargetTriple().isOSAIX())
+    return new PPCAIXAsmPrinter(tm, std::move(Streamer));
+
   return new PPCLinuxAsmPrinter(tm, std::move(Streamer));
 }
 
 // Force static initialization.
 extern "C" void LLVMInitializePowerPCAsmPrinter() {
   TargetRegistry::RegisterAsmPrinter(getThePPC32Target(),
                                      createPPCAsmPrinterPass);
   TargetRegistry::RegisterAsmPrinter(getThePPC64Target(),
                                      createPPCAsmPrinterPass);
   TargetRegistry::RegisterAsmPrinter(getThePPC64LETarget(),
                                      createPPCAsmPrinterPass);
 }

llvm/test/CodeGen/PowerPC/aix-xcoff-basic.ll

+; RUN: llc -mtriple powerpc-ibm-aix-xcoff -filetype=obj -o %t.o < %s
+; RUN: llvm-readobj --file-headers %t.o | FileCheck %s
+
+; RUN: not llc -mtriple powerpc64-ibm-aix-xcoff -filetype=obj < %s 2>&1 | \
+; RUN: FileCheck --check-prefix=64BIT %s
+
+target datalayout = "E-m:e-p:32:32-i64:64-n32"
+target triple = "powerpc-unknown-aix"
+
+; CHECK:      Format: aixcoff-rs6000
+; CHECK-NEXT: Arch: powerpc
+; CHECK-NEXT: AddressSize: 32bit
+; CHECK-NEXT: FileHeader {
+; CHECK-NEXT:   Magic: 0x1DF
+; CHECK-NEXT:   NumberOfSections: 0
+; CHECK-NEXT:   TimeStamp: None (0x0)
+; CHECK-NEXT:   SymbolTableOffset: 0x0
+; CHECK-NEXT:   SymbolTableEntries: 0
+; CHECK-NEXT:   OptionalHeaderSize: 0x0
+; CHECK-NEXT:   Flags: 0x0
+; CHECK-NEXT: }
+
+; 64BIT: LLVM ERROR: 64-bit XCOFF object files are not supported yet.