Support new dylink.0 custom section format (#4141)

See also:
spec change: WebAssembly/tool-conventions#170
llvm change: https://reviews.llvm.org/D109595
wabt change: WebAssembly/wabt#1707
emscripten change: emscripten-core/emscripten#15019

src/wasm-binary.h

@@ -403,6 +403,7 @@ namespace UserSections {
 extern const char* Name;
 extern const char* SourceMapUrl;
 extern const char* Dylink;
+extern const char* Dylink0;
 extern const char* Linking;
 extern const char* Producers;
 extern const char* TargetFeatures;
@@ -435,7 +436,10 @@ enum Subsection {
   NameElem = 8,
   NameData = 9,
   // see: https://github.com/WebAssembly/gc/issues/193
-  NameField = 10
+  NameField = 10,
+
+  DylinkMemInfo = 1,
+  DylinkNeeded = 2,
 };
 
 } // namespace UserSections
@@ -1230,6 +1234,7 @@ class WasmBinaryWriter {
   void writeUserSection(const UserSection& section);
   void writeFeaturesSection();
   void writeDylinkSection();
+  void writeLegacyDylinkSection();
 
   void initializeDebugInfo();
   void writeSourceMapProlog();
@@ -1557,6 +1562,7 @@ class WasmBinaryBuilder {
   void readNames(size_t);
   void readFeatures(size_t);
   void readDylink(size_t);
+  void readDylink0(size_t);
 
   // Debug information reading helpers
   void setDebugLocations(std::istream* sourceMap_) { sourceMap = sourceMap_; }

src/wasm.h

@@ -1833,6 +1833,7 @@ class UserSection {
 // The optional "dylink" section is used in dynamic linking.
 class DylinkSection {
 public:
+  bool isLegacy = false;
   Index memorySize, memoryAlignment, tableSize, tableAlignment;
   std::vector<Name> neededDynlibs;
   std::vector<char> tail;

src/wasm/wasm-binary.cpp

@@ -1067,7 +1067,7 @@ void WasmBinaryWriter::writeFeaturesSection() {
   finishSection(start);
 }
 
-void WasmBinaryWriter::writeDylinkSection() {
+void WasmBinaryWriter::writeLegacyDylinkSection() {
   if (!wasm->dylinkSection) {
     return;
   }
@@ -1082,9 +1082,41 @@ void WasmBinaryWriter::writeDylinkSection() {
   for (auto& neededDynlib : wasm->dylinkSection->neededDynlibs) {
     writeInlineString(neededDynlib.c_str());
   }
+  finishSection(start);
+}
 
-  writeData(wasm->dylinkSection->tail.data(), wasm->dylinkSection->tail.size());
+void WasmBinaryWriter::writeDylinkSection() {
+  if (!wasm->dylinkSection) {
+    return;
+  }
+
+  if (wasm->dylinkSection->isLegacy) {
+    writeLegacyDylinkSection();
+    return;
+  }
+
+  auto start = startSection(BinaryConsts::User);
+  writeInlineString(BinaryConsts::UserSections::Dylink0);
+
+  auto substart =
+    startSubsection(BinaryConsts::UserSections::Subsection::DylinkMemInfo);
+  o << U32LEB(wasm->dylinkSection->memorySize);
+  o << U32LEB(wasm->dylinkSection->memoryAlignment);
+  o << U32LEB(wasm->dylinkSection->tableSize);
+  o << U32LEB(wasm->dylinkSection->tableAlignment);
+  finishSubsection(substart);
+
+  if (wasm->dylinkSection->neededDynlibs.size()) {
+    substart =
+      startSubsection(BinaryConsts::UserSections::Subsection::DylinkNeeded);
+    o << U32LEB(wasm->dylinkSection->neededDynlibs.size());
+    for (auto& neededDynlib : wasm->dylinkSection->neededDynlibs) {
+      writeInlineString(neededDynlib.c_str());
+    }
+    finishSubsection(substart);
+  }
 
+  writeData(wasm->dylinkSection->tail.data(), wasm->dylinkSection->tail.size());
   finishSection(start);
 }
 
@@ -1435,6 +1467,7 @@ void WasmBinaryBuilder::read() {
 }
 
 void WasmBinaryBuilder::readUserSection(size_t payloadLen) {
+  BYN_TRACE("== readUserSection\n");
   auto oldPos = pos;
   Name sectionName = getInlineString();
   size_t read = pos - oldPos;
@@ -1452,6 +1485,8 @@ void WasmBinaryBuilder::readUserSection(size_t payloadLen) {
     readFeatures(payloadLen);
   } else if (sectionName.equals(BinaryConsts::UserSections::Dylink)) {
     readDylink(payloadLen);
+  } else if (sectionName.equals(BinaryConsts::UserSections::Dylink0)) {
+    readDylink0(payloadLen);
   } else {
     // an unfamiliar custom section
     if (sectionName.equals(BinaryConsts::UserSections::Linking)) {
@@ -3252,6 +3287,7 @@ void WasmBinaryBuilder::readDylink(size_t payloadLen) {
 
   auto sectionPos = pos;
 
+  wasm.dylinkSection->isLegacy = true;
   wasm.dylinkSection->memorySize = getU32LEB();
   wasm.dylinkSection->memoryAlignment = getU32LEB();
   wasm.dylinkSection->tableSize = getU32LEB();
@@ -3262,12 +3298,50 @@ void WasmBinaryBuilder::readDylink(size_t payloadLen) {
     wasm.dylinkSection->neededDynlibs.push_back(getInlineString());
   }
 
-  size_t remaining = (sectionPos + payloadLen) - pos;
-  auto tail = getByteView(remaining);
-  wasm.dylinkSection->tail = {tail.first, tail.second};
-
   if (pos != sectionPos + payloadLen) {
-    throwError("bad features section size");
+    throwError("bad dylink section size");
+  }
+}
+
+void WasmBinaryBuilder::readDylink0(size_t payloadLen) {
+  BYN_TRACE("== readDylink0\n");
+  auto sectionPos = pos;
+  uint32_t lastType = 0;
+
+  wasm.dylinkSection = make_unique<DylinkSection>();
+  while (pos < sectionPos + payloadLen) {
+    auto oldPos = pos;
+    auto dylinkType = getU32LEB();
+    if (lastType && dylinkType <= lastType) {
+      std::cerr << "warning: out-of-order dylink.0 subsection: " << dylinkType
+                << std::endl;
+    }
+    lastType = dylinkType;
+    auto subsectionSize = getU32LEB();
+    auto subsectionPos = pos;
+    if (dylinkType == BinaryConsts::UserSections::Subsection::DylinkMemInfo) {
+      wasm.dylinkSection->memorySize = getU32LEB();
+      wasm.dylinkSection->memoryAlignment = getU32LEB();
+      wasm.dylinkSection->tableSize = getU32LEB();
+      wasm.dylinkSection->tableAlignment = getU32LEB();
+    } else if (dylinkType ==
+               BinaryConsts::UserSections::Subsection::DylinkNeeded) {
+      size_t numNeededDynlibs = getU32LEB();
+      for (size_t i = 0; i < numNeededDynlibs; ++i) {
+        wasm.dylinkSection->neededDynlibs.push_back(getInlineString());
+      }
+    } else {
+      // Unknown subsection.  Stop parsing now and store the rest of
+      // the section verbatim.
+      pos = oldPos;
+      size_t remaining = (sectionPos + payloadLen) - pos;
+      auto tail = getByteView(remaining);
+      wasm.dylinkSection->tail = {tail.first, tail.second};
+      break;
+    }
+    if (pos != subsectionPos + subsectionSize) {
+      throwError("bad dylink.0 subsection position change");
+    }
   }
 }
 

src/wasm/wasm.cpp

@@ -31,6 +31,7 @@ namespace UserSections {
 const char* Name = "name";
 const char* SourceMapUrl = "sourceMappingURL";
 const char* Dylink = "dylink";
+const char* Dylink0 = "dylink.0";
 const char* Linking = "linking";
 const char* Producers = "producers";
 const char* TargetFeatures = "target_features";

test/lit/binary/dylink.test

@@ -3,13 +3,13 @@
 # `dylink.test.wasm` was generated using emscripten to build a side
 # module with two TLS exports (which adds extra information to the
 # dylink section) using:
-#  `emcc -s SIDE_MODULE side.c`
+#  `emcc -s USE_PTHREAD -s SIDE_MODULE side.c`
 #
 # side.c:
 #   _Thread_local int foo = 10;
 #   _Thread_local int bar = 11;
 #
-# and then removing all sections except the dylink section using:
-#  `llvm-objcopy --only-section=dylink`
+# and then removing all sections except the dylink.0 section using:
+#  `llvm-objcopy --only-section=dylink.0`
 RUN: wasm-opt -O1 %s.wasm -o %t.o
 RUN: cmp %s.wasm %t.o