[WebAssembly] Add support for init functions linking metadata

Summary:
This change lays the groundwork lowering of @llvm.global_ctors
and @llvm.global_dtors for the wasm object format.  Some parts
of this patch are subset of: https://reviews.llvm.org/D40759

See https://github.com/WebAssembly/tool-conventions/issues/25

Subscribers: jfb, dschuff, jgravelle-google, aheejin, sunfish

Differential Revision: https://reviews.llvm.org/D41208

llvm-svn: 320742

llvm/include/llvm/BinaryFormat/Wasm.h

@@ -115,8 +115,14 @@ struct WasmRelocation {
   int64_t Addend;  // A value to add to the symbol.
 };
 
+struct WasmInitFunc {
+  uint32_t Priority;
+  uint32_t FunctionIndex;
+};
+
 struct WasmLinkingData {
   uint32_t DataSize;
+  std::vector<WasmInitFunc> InitFunctions;
 };
 
 enum : unsigned {
@@ -185,6 +191,7 @@ enum : unsigned {
   WASM_SYMBOL_INFO    = 0x2,
   WASM_DATA_SIZE      = 0x3,
   WASM_SEGMENT_INFO   = 0x5,
+  WASM_INIT_FUNCS     = 0x6,
 };
 
 const unsigned WASM_SYMBOL_BINDING_MASK       = 0x3;

llvm/include/llvm/Object/Wasm.h

@@ -206,6 +206,7 @@ public:
   bool isRelocatableObject() const override;
 
 private:
+  bool isValidFunctionIndex(uint32_t Index) const;
   const WasmSection &getWasmSection(DataRefImpl Ref) const;
   const wasm::WasmRelocation &getWasmRelocation(DataRefImpl Ref) const;
 

llvm/include/llvm/ObjectYAML/WasmYAML.h

@@ -131,6 +131,11 @@ struct SymbolInfo {
   SymbolFlags Flags;
 };
 
+struct InitFunction {
+  uint32_t Priority;
+  uint32_t FunctionIndex;
+};
+
 struct Section {
   explicit Section(SectionType SecType) : Type(SecType) {}
   virtual ~Section();
@@ -173,6 +178,7 @@ struct LinkingSection : CustomSection {
   uint32_t DataSize;
   std::vector<SymbolInfo> SymbolInfos;
   std::vector<SegmentInfo> SegmentInfos;
+  std::vector<InitFunction> InitFunctions;
 };
 
 struct TypeSection : Section {
@@ -309,6 +315,7 @@ LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::Relocation)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::NameEntry)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::SegmentInfo)
 LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::SymbolInfo)
+LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::WasmYAML::InitFunction)
 
 namespace llvm {
 namespace yaml {
@@ -401,6 +408,10 @@ template <> struct MappingTraits<WasmYAML::SymbolInfo> {
   static void mapping(IO &IO, WasmYAML::SymbolInfo &Info);
 };
 
+template <> struct MappingTraits<WasmYAML::InitFunction> {
+  static void mapping(IO &IO, WasmYAML::InitFunction &Init);
+};
+
 template <> struct ScalarEnumerationTraits<WasmYAML::ValueType> {
   static void enumeration(IO &IO, WasmYAML::ValueType &Type);
 };

llvm/lib/Object/WasmObjectFile.cpp

@@ -398,6 +398,21 @@ Error WasmObjectFile::parseLinkingSection(const uint8_t *Ptr,
       }
       break;
     }
+    case wasm::WASM_INIT_FUNCS: {
+      uint32_t Count = readVaruint32(Ptr);
+      LinkingData.InitFunctions.reserve(Count);
+      for (uint32_t i = 0; i < Count; i++) {
+        wasm::WasmInitFunc Init;
+        Init.Priority = readVaruint32(Ptr);
+        Init.FunctionIndex = readVaruint32(Ptr);
+        if (!isValidFunctionIndex(Init.FunctionIndex))
+          return make_error<GenericBinaryError>("Invalid function index: " +
+                                                    Twine(Init.FunctionIndex),
+                                                object_error::parse_failed);
+        LinkingData.InitFunctions.emplace_back(Init);
+      }
+      break;
+    }
     default:
       Ptr += Size;
       break;
@@ -656,9 +671,13 @@ Error WasmObjectFile::parseExportSection(const uint8_t *Ptr, const uint8_t *End)
   return Error::success();
 }
 
+bool WasmObjectFile::isValidFunctionIndex(uint32_t Index) const {
+  return Index < FunctionTypes.size() + NumImportedFunctions;
+}
+
 Error WasmObjectFile::parseStartSection(const uint8_t *Ptr, const uint8_t *End) {
   StartFunction = readVaruint32(Ptr);
-  if (StartFunction >= FunctionTypes.size())
+  if (!isValidFunctionIndex(StartFunction))
     return make_error<GenericBinaryError>("Invalid start function",
                                           object_error::parse_failed);
   return Error::success();

llvm/lib/ObjectYAML/WasmYAML.cpp

@@ -60,6 +60,7 @@ static void sectionMapping(IO &IO, WasmYAML::LinkingSection &Section) {
   IO.mapRequired("DataSize", Section.DataSize);
   IO.mapOptional("SymbolInfo", Section.SymbolInfos);
   IO.mapOptional("SegmentInfo", Section.SegmentInfos);
+  IO.mapOptional("InitFunctions", Section.InitFunctions);
 }
 
 static void sectionMapping(IO &IO, WasmYAML::CustomSection &Section) {
@@ -359,6 +360,12 @@ void MappingTraits<WasmYAML::DataSegment>::mapping(
   IO.mapRequired("Content", Segment.Content);
 }
 
+void MappingTraits<WasmYAML::InitFunction>::mapping(
+    IO &IO, WasmYAML::InitFunction &Init) {
+  IO.mapRequired("Priority", Init.Priority);
+  IO.mapRequired("FunctionIndex", Init.FunctionIndex);
+}
+
 void MappingTraits<WasmYAML::SymbolInfo>::mapping(IO &IO,
                                                   WasmYAML::SymbolInfo &Info) {
   IO.mapRequired("Name", Info.Name);

llvm/test/ObjectYAML/wasm/linking_section.yaml

@@ -41,6 +41,9 @@ Sections:
         Alignment:   2
         Flags:       [ ]
         Name:        moredata
+    InitFunctions:
+      - Priority:      1
+        FunctionIndex: 0
 ...
 # CHECK:       - Type:            CUSTOM
 # CHECK-NEXT:    Name:            linking
@@ -57,4 +60,7 @@ Sections:
 # CHECK-NEXT:        Name:            moredata
 # CHECK-NEXT:        Alignment:       2
 # CHECK-NEXT:        Flags:           [ ]
+# CHECK-NEXT:    InitFunctions:
+# CHECK-NEXT:       - Priority:       1
+# CHECK-NEXT:         FunctionIndex:  0
 # CHECK-NEXT: ...

llvm/tools/obj2yaml/wasm2yaml.cpp

@@ -80,11 +80,15 @@ std::unique_ptr<WasmYAML::CustomSection> WasmDumper::dumpCustomSection(const Was
     for (const object::SymbolRef& Sym: Obj.symbols()) {
       const object::WasmSymbol Symbol = Obj.getWasmSymbol(Sym);
       if (Symbol.Flags != 0) {
-        WasmYAML::SymbolInfo Info = { Symbol.Name, Symbol.Flags };
+        WasmYAML::SymbolInfo Info{Symbol.Name, Symbol.Flags};
-        LinkingSec->SymbolInfos.push_back(Info);
+        LinkingSec->SymbolInfos.emplace_back(Info);
       }
     }
     LinkingSec->DataSize = Obj.linkingData().DataSize;
+    for (const wasm::WasmInitFunc &Func : Obj.linkingData().InitFunctions) {
+      WasmYAML::InitFunction F{Func.Priority, Func.FunctionIndex};
+      LinkingSec->InitFunctions.emplace_back(F);
+    }
     CustomSec = std::move(LinkingSec);
   } else {
     CustomSec = make_unique<WasmYAML::CustomSection>(WasmSec.Name);

llvm/tools/yaml2obj/yaml2wasm.cpp

@@ -162,6 +162,17 @@ int WasmWriter::writeSectionContent(raw_ostream &OS, WasmYAML::LinkingSection &S
     }
     SubSection.Done();
   }
+
+  // INIT_FUNCS subsection
+  if (Section.InitFunctions.size()) {
+    encodeULEB128(wasm::WASM_INIT_FUNCS, OS);
+    encodeULEB128(Section.InitFunctions.size(), SubSection.GetStream());
+    for (const WasmYAML::InitFunction &Func : Section.InitFunctions) {
+      encodeULEB128(Func.Priority, SubSection.GetStream());
+      encodeULEB128(Func.FunctionIndex, SubSection.GetStream());
+    }
+    SubSection.Done();
+  }
   return 0;
 }