[WebAssembly] Parse llvm.ident into producers section

[tlively]

Summary

Everything before the word "version" is the tool, and everything after
the word "version" is the version.

[tlively]

This patch seems to break llvm-dwarfdump, used by emscripten with -g, so I will need to make further changes and probably add new tests.

[tlively]

In D56742#1358674, @tlively wrote:

This patch seems to break llvm-dwarfdump, used by emscripten with -g, so I will need to make further changes and probably add new tests.

Actually, it turns out that this is a linker bug. The linker does not know about the producers section yet, so the section ends up being placed before the name section, which makes the resulting binary invalid as far as LLVM is concerned. The fix is to implement proper producers section support in lld. Coming soon.

[aheejin]

• Where do you actually put the contents into the binary producer section? YAML result does not show anything.
• Does object file reader support come later as a separate patch?

[aheejin]

In D56742#1358684, @tlively wrote:

In D56742#1358674, @tlively wrote:

This patch seems to break llvm-dwarfdump, used by emscripten with -g, so I will need to make further changes and probably add new tests.

Actually, it turns out that this is a linker bug. The linker does not know about the producers section yet, so the section ends up being placed before the name section, which makes the resulting binary invalid as far as LLVM is concerned. The fix is to implement proper producers section support in lld. Coming soon.

Why would linker have to know about custom section to make this patch work? We didn't run any linker tests in this patch, did we?

[sbc100]

Nice!

We could teach ObjectYAML to understand the contents but I don't think that is necessary for this change.

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

155

What if version is not part of the ident? Is that legal?

[tlively]

In D56742#1358698, @aheejin wrote:

Where do you actually put the contents into the binary producer section? YAML result does not show anything.

See WebAssemblyAsmPrinter.cpp

In D56742#1358702, @aheejin wrote:

In D56742#1358684, @tlively wrote:

In D56742#1358674, @tlively wrote:

This patch seems to break llvm-dwarfdump, used by emscripten with -g, so I will need to make further changes and probably add new tests.

Actually, it turns out that this is a linker bug. The linker does not know about the producers section yet, so the section ends up being placed before the name section, which makes the resulting binary invalid as far as LLVM is concerned. The fix is to implement proper producers section support in lld. Coming soon.

Why would linker have to know to make this patch work? We didn't run any linker tests in this patch, did we?

It's more like the linker is broken in the presence of producers sections, but we didn't know until now because we never had producers sections.

[tlively]

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

155

In that case the entire llvm.ident string will be taken as the tool and the version string will be empty.

[dschuff]

As a follow-on, I guess we could get ambitious and add the "language" field as well. I think the only way to do that would be to sniff the language field of the DICompileUnit metadata node (it would of course only exist if there's debug info, but doing anything else seems a bit crazytown).

[tlively]

• Add ObjectYAML support and tests
• Restrict producers to be unique by name

[dschuff]

lib/ObjectYAML/WasmYAML.cpp

79

Shouldn't these all be optional?

[sbc100]

include/llvm/Object/Wasm.h

160

Could we keep this interface simpler by putting these in a struct and have "getProducerInfo()" (see DylinkInfo).

Otherwise lgtm

[tlively]

• Make YAML fields optional, change to getProducerInfo interface

include/llvm/Object/Wasm.h

public:
   ArrayRef<wasm::WasmElemSegment> elements() const { return ElemSegments; }
   ArrayRef<WasmSegment> dataSegments() const { return DataSegments; }
   ArrayRef<wasm::WasmFunction> functions() const { return Functions; }
   ArrayRef<wasm::WasmFunctionName> debugNames() const { return DebugNames; }
   uint32_t startFunction() const { return StartFunction; }
   uint32_t getNumImportedGlobals() const { return NumImportedGlobals; }
   uint32_t getNumImportedFunctions() const { return NumImportedFunctions; }
   uint32_t getNumImportedEvents() const { return NumImportedEvents; }
+  std::vector<std::pair<std::string, std::string>> getLanguages() const {
+    return Languages;
+  }
+  std::vector<std::pair<std::string, std::string>> getTools() const {
+    return Tools;
+  }
+  std::vector<std::pair<std::string, std::string>> getSDKs() const {
+    return SDKs;
+  }
 
   void moveSymbolNext(DataRefImpl &Symb) const override;
 
   uint32_t getSymbolFlags(DataRefImpl Symb) const override;
 
   basic_symbol_iterator symbol_begin() const override;
 
   basic_symbol_iterator symbol_end() const override;
private:
   Error parseDataSection(ReadContext &Ctx);
 
   // Custom section types
   Error parseDylinkSection(ReadContext &Ctx);
   Error parseNameSection(ReadContext &Ctx);
   Error parseLinkingSection(ReadContext &Ctx);
   Error parseLinkingSectionSymtab(ReadContext &Ctx);
   Error parseLinkingSectionComdat(ReadContext &Ctx);
+  Error parseProducersSection(ReadContext &Ctx);
   Error parseRelocSection(StringRef Name, ReadContext &Ctx);
 
   wasm::WasmObjectHeader Header;
   std::vector<WasmSection> Sections;
   wasm::WasmDylinkInfo DylinkInfo;
   std::vector<wasm::WasmSignature> Signatures;
   std::vector<uint32_t> FunctionTypes;
   std::vector<wasm::WasmTable> Tables;
   std::vector<wasm::WasmLimits> Memories;
   std::vector<wasm::WasmGlobal> Globals;
   std::vector<wasm::WasmEvent> Events;
   std::vector<wasm::WasmImport> Imports;
   std::vector<wasm::WasmExport> Exports;
   std::vector<wasm::WasmElemSegment> ElemSegments;
   std::vector<WasmSegment> DataSegments;
   std::vector<wasm::WasmFunction> Functions;
   std::vector<WasmSymbol> Symbols;
   std::vector<wasm::WasmFunctionName> DebugNames;
+  std::vector<std::pair<std::string, std::string>> Languages;
+  std::vector<std::pair<std::string, std::string>> Tools;
+  std::vector<std::pair<std::string, std::string>> SDKs;
   uint32_t StartFunction = -1;
   bool HasLinkingSection = false;
   bool HasDylinkSection = false;
   wasm::WasmLinkingData LinkingData;
   uint32_t NumImportedGlobals = 0;
   uint32_t NumImportedFunctions = 0;
   uint32_t NumImportedEvents = 0;
   uint32_t CodeSection = 0;

include/llvm/ObjectYAML/WasmYAML.h

struct DataSegment {
   yaml::BinaryRef Content;
 };
 
 struct NameEntry {
   uint32_t Index;
   StringRef Name;
 };
 
+struct ProducerEntry {
+  std::string Name;
+  std::string Version;
+};
+
 struct SegmentInfo {
   uint32_t Index;
   StringRef Name;
   uint32_t Alignment;
   SegmentFlags Flags;
 };
 
 struct Signature {
struct LinkingSection : CustomSection {
 
   uint32_t Version;
   std::vector<SymbolInfo> SymbolTable;
   std::vector<SegmentInfo> SegmentInfos;
   std::vector<InitFunction> InitFunctions;
   std::vector<Comdat> Comdats;
 };
 
+struct ProducersSection : CustomSection {
+  ProducersSection() : CustomSection("producers") {}
+
+  static bool classof(const Section *S) {
+    auto C = dyn_cast<CustomSection>(S);
+    return C && C->Name == "producers";
+  }
+
+  std::vector<ProducerEntry> Languages;
+  std::vector<ProducerEntry> Tools;
+  std::vector<ProducerEntry> SDKs;
+};
+
 struct TypeSection : Section {
   TypeSection() : Section(wasm::WASM_SEC_TYPE) {}
 
   static bool classof(const Section *S) {
     return S->Type == wasm::WASM_SEC_TYPE;
   }
 
   std::vector<Signature> Signatures;

 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::ElemSegment)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Limits)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::DataSegment)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Global)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Function)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::LocalDecl)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Relocation)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::NameEntry)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::ProducerEntry)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::SegmentInfo)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::SymbolInfo)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::InitFunction)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::ComdatEntry)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Comdat)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Event)
 
 namespace llvm {

 template <> struct MappingTraits<WasmYAML::Relocation> {
   static void mapping(IO &IO, WasmYAML::Relocation &Relocation);
 };
 
 template <> struct MappingTraits<WasmYAML::NameEntry> {
   static void mapping(IO &IO, WasmYAML::NameEntry &NameEntry);
 };
 
+template <> struct MappingTraits<WasmYAML::ProducerEntry> {
+  static void mapping(IO &IO, WasmYAML::ProducerEntry &ProducerEntry);
+};
+
 template <> struct MappingTraits<WasmYAML::SegmentInfo> {
   static void mapping(IO &IO, WasmYAML::SegmentInfo &SegmentInfo);
 };
 
 template <> struct MappingTraits<WasmYAML::LocalDecl> {
   static void mapping(IO &IO, WasmYAML::LocalDecl &LocalDecl);
 };
 

lib/MC/WasmObjectWriter.cpp

class WasmObjectWriter : public MCObjectWriter {
   // space.
   DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
   // Maps data symbols to the Wasm segment and offset/size with the segment.
   DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
 
   // Stores output data (index, relocations, content offset) for custom
   // section.
   std::vector<WasmCustomSection> CustomSections;
+  std::unique_ptr<WasmCustomSection> ProducersSection;
   // Relocations for fixing up references in the custom sections.
   DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
       CustomSectionsRelocations;
 
   // Map from section to defining function symbol.
   DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
 
   DenseMap<WasmSignature, uint32_t, WasmSignatureDenseMapInfo> SignatureIndices;

 private:
   void reset() override {
     CodeRelocations.clear();
     DataRelocations.clear();
     TypeIndices.clear();
     WasmIndices.clear();
     TableIndices.clear();
     DataLocations.clear();
+    CustomSections.clear();
+    ProducersSection.reset();
     CustomSectionsRelocations.clear();
     SignatureIndices.clear();
     Signatures.clear();
     Globals.clear();
     DataSegments.clear();
     SectionFunctions.clear();
     NumFunctionImports = 0;
     NumGlobalImports = 0;
private:
   void writeDataSection();
   void writeEventSection(ArrayRef<wasm::WasmEventType> Events);
   void writeRelocSection(uint32_t SectionIndex, StringRef Name,
                          std::vector<WasmRelocationEntry> &Relocations);
   void writeLinkingMetaDataSection(
       ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
       ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
       const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
-  void writeCustomSections(const MCAssembler &Asm, const MCAsmLayout &Layout);
+  void writeCustomSection(WasmCustomSection &CustomSection,
+                          const MCAssembler &Asm, const MCAsmLayout &Layout);
   void writeCustomRelocSections();
   void
   updateCustomSectionRelocations(const SmallVector<WasmFunction, 4> &Functions,
                                  const MCAsmLayout &Layout);
 
   uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
   void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
                         uint64_t ContentsOffset);
for (const auto &C : Comdats) {
       }
     }
     endSection(SubSection);
   }
 
   endSection(Section);
 }
 
-void WasmObjectWriter::writeCustomSections(const MCAssembler &Asm,
-                                           const MCAsmLayout &Layout) {
-  for (auto &CustomSection : CustomSections) {
-    SectionBookkeeping Section;
-    auto *Sec = CustomSection.Section;
-    startCustomSection(Section, CustomSection.Name);
+void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection,
+                                          const MCAssembler &Asm,
 
-    Sec->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
-    Asm.writeSectionData(W.OS, Sec, Layout);
 
-    CustomSection.OutputContentsOffset = Section.ContentsOffset;
-    CustomSection.OutputIndex = Section.Index;
 
-    endSection(Section);
 
-    // Apply fixups.
-    auto &Relocations = CustomSectionsRelocations[CustomSection.Section];
-    applyRelocations(Relocations, CustomSection.OutputContentsOffset);
-  }
-}
 
 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) {
   assert(Symbol.isFunction());
   assert(TypeIndices.count(&Symbol));
   return TypeIndices[&Symbol];
 }
 
 uint32_t WasmObjectWriter::getEventType(const MCSymbolWasm &Symbol) {
if (Section.isWasmData()) {
 
       MCSymbol *Begin = Sec.getBeginSymbol();
       if (Begin) {
         WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
         if (SectionName != Begin->getName())
           report_fatal_error("section name and begin symbol should match: " +
                              Twine(SectionName));
       }
+
+      // Separate out the producers section
+      if (Name == "producers") {
+        ProducersSection = llvm::make_unique<WasmCustomSection>(Name, &Section);
+        continue;
+      }
+
       CustomSections.emplace_back(Name, &Section);
     }
   }
 
   // Populate WasmIndices and DataLocations for defined symbols.
   for (const MCSymbol &S : Asm.symbols()) {
     // Ignore unnamed temporary symbols, which aren't ever exported, imported,
     // or used in relocations.
uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
   // Skip the "table" section; we import the table instead.
   // Skip the "memory" section; we import the memory instead.
   writeGlobalSection();
   writeEventSection(Events);
   writeExportSection(Exports);
   writeElemSection(TableElems);
   writeCodeSection(Asm, Layout, Functions);
   writeDataSection();
-  writeCustomSections(Asm, Layout);
+  for (auto &CustomSection : CustomSections)
+    writeCustomSection(CustomSection, Asm, Layout);
   writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
   writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
   writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
   writeCustomRelocSections();
+  if (ProducersSection)
+    writeCustomSection(*ProducersSection, Asm, Layout);
 
   // TODO: Translate the .comment section to the output.
   return W.OS.tell() - StartOffset;
 }
 
 std::unique_ptr<MCObjectWriter>
 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
                              raw_pwrite_stream &OS) {
   return llvm::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
 }

lib/Object/WasmObjectFile.cpp

 //===- WasmObjectFile.cpp - Wasm object file implementation ---------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/BinaryFormat/Wasm.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Object/Binary.h"
 #include "llvm/Object/Error.h"
 #include "llvm/Object/ObjectFile.h"
while (EntryCount--) {
         getDefinedFunction(Index).Comdat = ComdatIndex;
         break;
       }
     }
   }
   return Error::success();
 }
 
+Error WasmObjectFile::parseProducersSection(ReadContext &Ctx) {
+  llvm::SmallSet<StringRef, 3> FieldsSeen;
+  uint32_t Fields = readVaruint32(Ctx);
+  for (size_t i = 0; i < Fields; ++i) {
+    StringRef FieldName = readString(Ctx);
+    if (!FieldsSeen.insert(FieldName).second)
+      return make_error<GenericBinaryError>(
+          "Producers section does not have unique fields",
+          object_error::parse_failed);
+    std::vector<std::pair<std::string, std::string>> *ProducerVec = nullptr;
+    if (FieldName == "language") {
+      ProducerVec = &Languages;
+    } else if (FieldName == "processed-by") {
+      ProducerVec = &Tools;
+    } else if (FieldName == "sdk") {
+      ProducerVec = &SDKs;
+    } else {
+      return make_error<GenericBinaryError>(
+          "Producers section field is not named one of language, processed-by, "
+          "or sdk",
+          object_error::parse_failed);
+    }
+    uint32_t ValueCount = readVaruint32(Ctx);
+    llvm::SmallSet<StringRef, 8> ProducersSeen;
+    for (size_t j = 0; j < ValueCount; ++j) {
+      StringRef Name = readString(Ctx);
+      StringRef Version = readString(Ctx);
+      if (!ProducersSeen.insert(Name).second) {
+        return make_error<GenericBinaryError>(
+            "Producers section contains repeated producer",
+            object_error::parse_failed);
+      }
+      ProducerVec->emplace_back(Name, Version);
+    }
+  }
+  if (Ctx.Ptr != Ctx.End)
+    return make_error<GenericBinaryError>("Producers section ended prematurely",
+                                          object_error::parse_failed);
+  return Error::success();
+}
+
 Error WasmObjectFile::parseRelocSection(StringRef Name, ReadContext &Ctx) {
   uint32_t SectionIndex = readVaruint32(Ctx);
   if (SectionIndex >= Sections.size())
     return make_error<GenericBinaryError>("Invalid section index",
                                           object_error::parse_failed);
   WasmSection &Section = Sections[SectionIndex];
   uint32_t RelocCount = readVaruint32(Ctx);
   uint32_t EndOffset = Section.Content.size();
if (Sec.Name == "dylink") {
     if (Error Err = parseDylinkSection(Ctx))
       return Err;
   } else if (Sec.Name == "name") {
     if (Error Err = parseNameSection(Ctx))
       return Err;
   } else if (Sec.Name == "linking") {
     if (Error Err = parseLinkingSection(Ctx))
       return Err;
+  } else if (Sec.Name == "producers") {
+    if (Error Err = parseProducersSection(Ctx))
+      return Err;
   } else if (Sec.Name.startswith("reloc.")) {
     if (Error Err = parseRelocSection(Sec.Name, Ctx))
       return Err;
   }
   return Error::success();
 }
 
 Error WasmObjectFile::parseTypeSection(ReadContext &Ctx) {

lib/ObjectYAML/WasmYAML.cpp

static void sectionMapping(IO &IO, WasmYAML::LinkingSection &Section) {
   IO.mapRequired("Name", Section.Name);
   IO.mapRequired("Version", Section.Version);
   IO.mapOptional("SymbolTable", Section.SymbolTable);
   IO.mapOptional("SegmentInfo", Section.SegmentInfos);
   IO.mapOptional("InitFunctions", Section.InitFunctions);
   IO.mapOptional("Comdats", Section.Comdats);
 }
 
+static void sectionMapping(IO &IO, WasmYAML::ProducersSection &Section) {
+  commonSectionMapping(IO, Section);
+  IO.mapRequired("Name", Section.Name);
+  IO.mapRequired("Languages", Section.Languages);
+  IO.mapRequired("Tools", Section.Tools);
+  IO.mapRequired("SDKs", Section.SDKs);
+}
+
 static void sectionMapping(IO &IO, WasmYAML::CustomSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapRequired("Name", Section.Name);
   IO.mapRequired("Payload", Section.Payload);
 }
 
 static void sectionMapping(IO &IO, WasmYAML::TypeSection &Section) {
   commonSectionMapping(IO, Section);
case wasm::WASM_SEC_CUSTOM: {
     } else if (SectionName == "linking") {
       if (!IO.outputting())
         Section.reset(new WasmYAML::LinkingSection());
       sectionMapping(IO, *cast<WasmYAML::LinkingSection>(Section.get()));
     } else if (SectionName == "name") {
       if (!IO.outputting())
         Section.reset(new WasmYAML::NameSection());
       sectionMapping(IO, *cast<WasmYAML::NameSection>(Section.get()));
+    } else if (SectionName == "producers") {
+      if (!IO.outputting())
+        Section.reset(new WasmYAML::ProducersSection());
+      sectionMapping(IO, *cast<WasmYAML::ProducersSection>(Section.get()));
     } else {
       if (!IO.outputting())
         Section.reset(new WasmYAML::CustomSection(SectionName));
       sectionMapping(IO, *cast<WasmYAML::CustomSection>(Section.get()));
     }
     break;
   }
   case wasm::WASM_SEC_TYPE:

 }
 
 void MappingTraits<WasmYAML::NameEntry>::mapping(
     IO &IO, WasmYAML::NameEntry &NameEntry) {
   IO.mapRequired("Index", NameEntry.Index);
   IO.mapRequired("Name", NameEntry.Name);
 }
 
+void MappingTraits<WasmYAML::ProducerEntry>::mapping(
+    IO &IO, WasmYAML::ProducerEntry &ProducerEntry) {
+  IO.mapRequired("Name", ProducerEntry.Name);
+  IO.mapRequired("Version", ProducerEntry.Version);
+}
+
 void MappingTraits<WasmYAML::SegmentInfo>::mapping(
     IO &IO, WasmYAML::SegmentInfo &SegmentInfo) {
   IO.mapRequired("Index", SegmentInfo.Index);
   IO.mapRequired("Name", SegmentInfo.Name);
   IO.mapRequired("Alignment", SegmentInfo.Alignment);
   IO.mapRequired("Flags", SegmentInfo.Flags);
 }
 

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

 #include "WebAssemblyAsmPrinter.h"
 #include "InstPrinter/WebAssemblyInstPrinter.h"
 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
 #include "WebAssembly.h"
 #include "WebAssemblyMCInstLower.h"
 #include "WebAssemblyMachineFunctionInfo.h"
 #include "WebAssemblyRegisterInfo.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalVariable.h"
for (const Metadata *MD : Named->operands()) {
       std::string SectionName = (".custom_section." + Name->getString()).str();
       MCSectionWasm *mySection =
           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
       OutStreamer->SwitchSection(mySection);
       OutStreamer->EmitBytes(Contents->getString());
       OutStreamer->PopSection();
     }
   }
+
+  if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
+    llvm::SmallSet<StringRef, 4> SeenTools;
+    llvm::SmallVector<std::pair<StringRef, StringRef>, 4> Tools;
+    for (size_t i = 0, e = Ident->getNumOperands(); i < e; ++i) {
+      const auto *S = cast<MDString>(Ident->getOperand(i)->getOperand(0));
+      std::pair<StringRef, StringRef> Field = S->getString().split("version");
+      StringRef Name = Field.first.trim();
+      StringRef Version = Field.second.trim();
+      if (!SeenTools.insert(Name).second)
+        continue;
+      Tools.emplace_back(Name, Version);
+    }
+    MCSectionWasm *Producers = OutContext.getWasmSection(
+        ".custom_section.producers", SectionKind::getMetadata());
+    OutStreamer->PushSection();
+    OutStreamer->SwitchSection(Producers);
+    OutStreamer->EmitULEB128IntValue(1);
+    OutStreamer->EmitULEB128IntValue(strlen("processed-by"));
+    OutStreamer->EmitBytes("processed-by");
+    OutStreamer->EmitULEB128IntValue(Tools.size());
+    for (auto &Tool : Tools) {
+      OutStreamer->EmitULEB128IntValue(Tool.first.size());
+      OutStreamer->EmitBytes(Tool.first);
+      OutStreamer->EmitULEB128IntValue(Tool.second.size());
+      OutStreamer->EmitBytes(Tool.second);
+    }
+    OutStreamer->PopSection();
+  }
 }
 
 void WebAssemblyAsmPrinter::EmitConstantPool() {
   assert(MF->getConstantPool()->getConstants().empty() &&
          "WebAssembly disables constant pools");
 }
 
 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {

test/CodeGen/WebAssembly/custom-sections.ll

 ; RUN: llc < %s -asm-verbose=false | FileCheck %s
 
 ; Test the mechanism for defining user custom sections.
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 !0 = !{ !"red", !"foo" }
 !1 = !{ !"green", !"bar" }
 !2 = !{ !"green", !"qux" }
 !wasm.custom_sections = !{ !0, !1, !2 }
 
+!llvm.ident = !{!3}
+!3 = !{!"clang version 123"}
+
 ; CHECK:      .section  .custom_section.red,"",@
 ; CHECK-NEXT: .ascii  "foo"
 
 ; CHECK:      .section  .custom_section.green,"",@
 ; CHECK-NEXT: .ascii  "bar"
 
 ; CHECK:      .section  .custom_section.green,"",@
 ; CHECK-NEXT: .ascii  "qux"
+
+; CHECK:      .section  .custom_section.producers,"",@
+; CHECK-NEXT: .int8 1
+; CHECK-NEXT: .int8 12
+; CHECK-NEXT: .ascii  "processed-by"
+; CHECK-NEXT: .int8 1
+; CHECK-NEXT: .int8 5
+; CHECK-NEXT: .ascii  "clang"
+; CHECK-NEXT: .int8 3
+; CHECK-NEXT: .ascii  "123"

test/MC/WebAssembly/custom-sections.ll

 ; RUN: llc -filetype=obj %s -o - | llvm-readobj -s | FileCheck %s
 
 ; Test the mechanism for defining user custom sections.
 
 target triple = "wasm32-unknown-unknown"
 
 !0 = !{ !"red", !"foo" }
 !1 = !{ !"green", !"bar" }
 !2 = !{ !"green", !"qux" }
 !wasm.custom_sections = !{ !0, !1, !2 }
 
+!3 = !{ !"clang version 123"}
+!llvm.ident = !{!3}
+
 ; CHECK:  Section {
 ; CHECK:    Type: CUSTOM (0x0)
 ; CHECK:    Size: 3
 ; CHECK:    Offset: 72
 ; CHECK:    Name: red
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: CUSTOM (0x0)
 ; CHECK:    Size: 6
 ; CHECK:    Offset: 85
 ; CHECK:    Name: green
 ; CHECK:  }
+; CHECK:  Section {
+; CHECK:    Type: CUSTOM (0x0)
+; CHECK:    Size: 25
+; CHECK:    Offset: 118
+; CHECK:    Name: producers
+; CHECK:  }

test/MC/WebAssembly/debug-info.ll

 ; CHECK-NEXT:    Name: reloc..debug_pubtypes
 ; CHECK-NEXT:  }
 ; CHECK-NEXT:  Section {
 ; CHECK-NEXT:    Type: CUSTOM (0x0)
 ; CHECK-NEXT:    Size: 6
 ; CHECK-NEXT:    Offset: 991
 ; CHECK-NEXT:    Name: reloc..debug_line
 ; CHECK-NEXT:  }
+; CHECK-NEXT:  Section {
+; CHECK-NEXT:    Type: CUSTOM (0x0)
+; CHECK-NEXT:    Size: 62
+; CHECK-NEXT:    Offset: 1021
+; CHECK-NEXT:    Name: producers
+; CHECK-NEXT:  }
 ; CHECK-NEXT:]
 ; CHECK-NEXT:Relocations [
 ; CHECK-NEXT:  Section (6) DATA {
 ; CHECK-NEXT:    0x6 R_WEBASSEMBLY_MEMORY_ADDR_I32 myextern 0
 ; CHECK-NEXT:    0xF R_WEBASSEMBLY_TABLE_INDEX_I32 f2
 ; CHECK-NEXT:  }
 ; CHECK-NEXT:  Section (9) .debug_info {
 ; CHECK-NEXT:    0x6 R_WEBASSEMBLY_SECTION_OFFSET_I32 .debug_abbrev 0

test/ObjectYAML/wasm/producers_section.yaml

+# RUN: yaml2obj %s | obj2yaml | FileCheck %s
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            CUSTOM
+    Name:            producers
+    Languages:
+      - Name:        C++
+        Version:     C++11
+    Tools:
+      - Name:        clang
+        Version:     123
+    SDKs:
+      - Name:        emscripten
+        Version:     9001
+...
+# CHECK:  Sections:
+# CHECK:    - Type:            CUSTOM
+# CHECK:      Name:            producers
+# CHECK:      Languages:
+# CHECK:        - Name:        'C++'
+# CHECK:          Version:     'C++11'
+# CHECK:      Tools:
+# CHECK:        - Name:        clang
+# CHECK:          Version:     '123'
+# CHECK:      SDKs:
+# CHECK:        - Name:        emscripten
+# CHECK:          Version:     '9001'

test/ObjectYAML/wasm/producers_section_repeat.yaml

+# RUN: yaml2obj %s | not obj2yaml 2>&1 | FileCheck %s
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            CUSTOM
+    Name:            producers
+    Languages:
+      - Name:        C++
+        Version:     C++11
+      - Name:        C++
+        Version:     C++17
+    Tools: []
+    SDKs: []
+...
+# CHECK:  Producers section contains repeated producer

tools/obj2yaml/wasm2yaml.cpp

if (WasmSec.Name == "dylink") {
     }
 
     for (const wasm::WasmInitFunc &Func : Obj.linkingData().InitFunctions) {
       WasmYAML::InitFunction F{Func.Priority, Func.Symbol};
       LinkingSec->InitFunctions.emplace_back(F);
     }
 
     CustomSec = std::move(LinkingSec);
+  } else if (WasmSec.Name == "producers") {
+    std::unique_ptr<WasmYAML::ProducersSection> ProducersSec =
+        make_unique<WasmYAML::ProducersSection>();
+    for (auto &E : Obj.getLanguages()) {
+      WasmYAML::ProducerEntry Producer;
+      Producer.Name = E.first;
+      Producer.Version = E.second;
+      ProducersSec->Languages.push_back(Producer);
+    }
+    for (auto &E : Obj.getTools()) {
+      WasmYAML::ProducerEntry Producer;
+      Producer.Name = E.first;
+      Producer.Version = E.second;
+      ProducersSec->Tools.push_back(Producer);
+    }
+    for (auto &E : Obj.getSDKs()) {
+      WasmYAML::ProducerEntry Producer;
+      Producer.Name = E.first;
+      Producer.Version = E.second;
+      ProducersSec->SDKs.push_back(Producer);
+    }
+    CustomSec = std::move(ProducersSec);
   } else {
     CustomSec = make_unique<WasmYAML::CustomSection>(WasmSec.Name);
   }
   CustomSec->Payload = yaml::BinaryRef(WasmSec.Content);
   return CustomSec;
 }
 
 ErrorOr<WasmYAML::Object *> WasmDumper::dump() {

tools/yaml2obj/yaml2wasm.cpp

private:
   int writeSectionContent(raw_ostream &OS, WasmYAML::ElemSection &Section);
   int writeSectionContent(raw_ostream &OS, WasmYAML::CodeSection &Section);
   int writeSectionContent(raw_ostream &OS, WasmYAML::DataSection &Section);
 
   // Custom section types
   int writeSectionContent(raw_ostream &OS, WasmYAML::DylinkSection &Section);
   int writeSectionContent(raw_ostream &OS, WasmYAML::NameSection &Section);
   int writeSectionContent(raw_ostream &OS, WasmYAML::LinkingSection &Section);
+  int writeSectionContent(raw_ostream &OS, WasmYAML::ProducersSection &Section);
   WasmYAML::Object &Obj;
   uint32_t NumImportedFunctions = 0;
   uint32_t NumImportedGlobals = 0;
   uint32_t NumImportedEvents = 0;
 };
 
 static int writeUint64(raw_ostream &OS, uint64_t Value) {
   char Data[sizeof(Value)];
if (Section.FunctionNames.size()) {
     }
 
     SubSection.Done();
   }
   return 0;
 }
 
 int WasmWriter::writeSectionContent(raw_ostream &OS,
+                                    WasmYAML::ProducersSection &Section) {
+  writeStringRef(Section.Name, OS);
+  int Fields = int(!Section.Languages.empty()) + int(!Section.Tools.empty()) +
+               int(!Section.SDKs.empty());
+  if (Fields == 0)
+    return 0;
+  encodeULEB128(Fields, OS);
+  for (auto &Field : {std::make_pair(StringRef("language"), Section.Languages),
+                      std::make_pair(StringRef("processed-by"), Section.Tools),
+                      std::make_pair(StringRef("sdk"), Section.SDKs)}) {
+    if (Field.second.empty())
+      continue;
+    writeStringRef(Field.first, OS);
+    encodeULEB128(Field.second.size(), OS);
+    for (auto &Entry : Field.second) {
+      writeStringRef(Entry.Name, OS);
+      writeStringRef(Entry.Version, OS);
+    }
+  }
+  return 0;
+}
+
+int WasmWriter::writeSectionContent(raw_ostream &OS,
                                     WasmYAML::CustomSection &Section) {
   if (auto S = dyn_cast<WasmYAML::DylinkSection>(&Section)) {
     if (auto Err = writeSectionContent(OS, *S))
       return Err;
   } else if (auto S = dyn_cast<WasmYAML::NameSection>(&Section)) {
     if (auto Err = writeSectionContent(OS, *S))
       return Err;
   } else if (auto S = dyn_cast<WasmYAML::LinkingSection>(&Section)) {
     if (auto Err = writeSectionContent(OS, *S))
       return Err;
+  } else if (auto S = dyn_cast<WasmYAML::ProducersSection>(&Section)) {
+    if (auto Err = writeSectionContent(OS, *S))
+      return Err;
   } else {
     writeStringRef(Section.Name, OS);
     Section.Payload.writeAsBinary(OS);
   }
   return 0;
 }
 
 int WasmWriter::writeSectionContent(raw_ostream &OS,