Extensible name section (#933)

See #914.

* extensible name section support: read function names, too

* c-api-unused-mem.txt: change expected size to match new name section

* * check subsection size matches

* print warning for unknown name subsections (including the local
  section)

Author: pipcet

src/wasm-binary.h

@@ -303,6 +303,11 @@ enum EncodedType {
 
 namespace UserSections {
 extern const char* Name;
+
+enum Subsection {
+  NameFunction = 1,
+  NameLocal = 2,
+};
 }
 
 enum ASTNodes {
@@ -545,6 +550,8 @@ class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
   void writeResizableLimits(Address initial, Address maximum, bool hasMaximum);
   int32_t startSection(BinaryConsts::Section code);
   void finishSection(int32_t start);
+  int32_t startSubsection(BinaryConsts::UserSections::Subsection code);
+  void finishSubsection(int32_t start);
   void writeStart();
   void writeMemory();
   void writeTypes();
@@ -721,7 +728,7 @@ class WasmBinaryBuilder {
 
   void readFunctionTableDeclaration();
   void readTableElements();
-  void readNames();
+  void readNames(size_t);
 
   // AST reading
   int depth = 0; // only for debugging

src/wasm/wasm-binary.cpp

@@ -83,6 +83,16 @@ void WasmBinaryWriter::finishSection(int32_t start) {
   o.writeAt(start, U32LEB(size));
 }
 
+int32_t WasmBinaryWriter::startSubsection(BinaryConsts::UserSections::Subsection code) {
+  o << U32LEB(code);
+  return writeU32LEBPlaceholder(); // section size to be filled in later
+}
+
+void WasmBinaryWriter::finishSubsection(int32_t start) {
+  int32_t size = o.size() - start - 5; // section size does not include the 5 bytes of the size field itself
+  o.writeAt(start, U32LEB(size));
+}
+
 void WasmBinaryWriter::writeStart() {
   if (!wasm->start.is()) return;
   if (debug) std::cerr << "== writeStart" << std::endl;
@@ -389,21 +399,24 @@ void WasmBinaryWriter::writeNames() {
   if (debug) std::cerr << "== writeNames" << std::endl;
   auto start = startSection(BinaryConsts::Section::User);
   writeInlineString(BinaryConsts::UserSections::Name);
+  auto substart = startSubsection(BinaryConsts::UserSections::Subsection::NameFunction);
   o << U32LEB(mappedFunctions.size());
   Index emitted = 0;
   for (auto& import : wasm->imports) {
     if (import->kind == ExternalKind::Function) {
+      o << U32LEB(emitted);
       writeInlineString(import->name.str);
-      o << U32LEB(0); // TODO: locals
       emitted++;
     }
   }
   for (auto& curr : wasm->functions) {
+    o << U32LEB(emitted);
     writeInlineString(curr->name.str);
-    o << U32LEB(0); // TODO: locals
     emitted++;
   }
   assert(emitted == mappedFunctions.size());
+  finishSubsection(substart);
+  /* TODO: locals */
   finishSection(start);
 }
 
@@ -969,7 +982,7 @@ void WasmBinaryBuilder::readUserSection(size_t payloadLen) {
   auto oldPos = pos;
   Name sectionName = getInlineString();
   if (sectionName.equals(BinaryConsts::UserSections::Name)) {
-    readNames();
+    readNames(payloadLen - (pos - oldPos));
   } else {
     // an unfamiliar custom section
     wasm.userSections.resize(wasm.userSections.size() + 1);
@@ -1510,25 +1523,36 @@ void WasmBinaryBuilder::readTableElements() {
   }
 }
 
-void WasmBinaryBuilder::readNames() {
+void WasmBinaryBuilder::readNames(size_t payloadLen) {
   if (debug) std::cerr << "== readNames" << std::endl;
-  auto num = getU32LEB();
-  if (num == 0) return;
-  for (auto& import : wasm.imports) {
-    if (import->kind == ExternalKind::Function) {
-      getInlineString(); // TODO: use this
-      auto numLocals = getU32LEB();
-      WASM_UNUSED(numLocals);
-      assert(numLocals == 0); // TODO
-      if (--num == 0) return;
+  auto sectionPos = pos;
+  while (pos < sectionPos + payloadLen) {
+    auto nameType = getU32LEB();
+    auto subsectionSize = getU32LEB();
+    auto subsectionPos = pos;
+    if (nameType != BinaryConsts::UserSections::Subsection::NameFunction) {
+      // TODO: locals
+      std::cerr << "unknown name subsection at " << pos << std::endl;
+      pos = subsectionPos + subsectionSize;
+      continue;
     }
+    auto num = getU32LEB();
+    uint32_t importedFunctions = 0;
+    for (auto& import : wasm.imports) {
+      if (import->kind != ExternalKind::Function) continue;
+      importedFunctions++;
+    }
+    for (size_t i = 0; i < num; i++) {
+      auto index = getU32LEB();
+      if (index < importedFunctions) {
+        getInlineString(); // TODO: use this
+      } else if (index - importedFunctions < functions.size()) {
+        functions[index - importedFunctions]->name = getInlineString();
+      }
+    }
+    assert(pos == subsectionPos + subsectionSize);
   }
-  for (size_t i = 0; i < num; i++) {
-    functions[i]->name = getInlineString();
-    auto numLocals = getU32LEB();
-    WASM_UNUSED(numLocals);
-    assert(numLocals == 0); // TODO
-  }
+  assert(pos == sectionPos + payloadLen);
 }
 
 BinaryConsts::ASTNodes WasmBinaryBuilder::readExpression(Expression*& curr) {

test/example/c-api-unused-mem.txt

@@ -46,7 +46,7 @@
   (call $main)
  )
 )
-207
+213
 (module
  (type $0 (func))
  (type $1 (func))