wasm-emscripten-finalize: Initial support for handling shared libraries (#1746)

In this case we won't want generate any of the normal memory
helper functions (they come from the main module).

Author: sbc100

src/tools/wasm-emscripten-finalize.cpp

@@ -130,19 +130,30 @@ int main(int argc, const char *argv[]) {
     WasmPrinter::printModule(&wasm, std::cerr);
   }
 
-  Export* dataEndExport = wasm.getExport("__data_end");
-  if (dataEndExport == nullptr) {
-    Fatal() << "__data_end export not found";
+  bool isSideModule = false;
+  for (const UserSection& section : wasm.userSections) {
+    if (section.name == BinaryConsts::UserSections::Dylink) {
+      isSideModule = true;
+    }
   }
-  Global* dataEnd = wasm.getGlobal(dataEndExport->value);
-  if (dataEnd == nullptr) {
-    Fatal() << "__data_end global not found";
-  }
-  if (dataEnd->type != Type::i32) {
-    Fatal() << "__data_end global has wrong type";
+
+  uint32_t dataSize = 0;
+
+  if (!isSideModule) {
+    Export* dataEndExport = wasm.getExport("__data_end");
+    if (dataEndExport == nullptr) {
+      Fatal() << "__data_end export not found";
+    }
+    Global* dataEnd = wasm.getGlobal(dataEndExport->value);
+    if (dataEnd == nullptr) {
+      Fatal() << "__data_end global not found";
+    }
+    if (dataEnd->type != Type::i32) {
+      Fatal() << "__data_end global has wrong type";
+    }
+    Const* dataEndConst = dataEnd->init->cast<Const>();
+    dataSize = dataEndConst->value.geti32() - globalBase;
   }
-  Const* dataEndConst = dataEnd->init->cast<Const>();
-  uint32_t dataSize = dataEndConst->value.geti32() - globalBase;
 
   std::vector<Name> initializerFunctions;
   if (wasm.getFunctionOrNull("__wasm_call_ctors")) {
@@ -160,8 +171,10 @@ int main(int argc, const char *argv[]) {
     passRunner.run();
   }
 
-  generator.generateRuntimeFunctions();
-  generator.generateMemoryGrowthFunction();
+  if (!isSideModule) {
+    generator.generateRuntimeFunctions();
+    generator.generateMemoryGrowthFunction();
+  }
   generator.generateDynCallThunks();
   generator.generateJSCallThunks(numReservedFunctionPointers);
   std::string metadata = generator.generateEmscriptenMetadata(dataSize, initializerFunctions, numReservedFunctionPointers);

src/wasm-emscripten.h

@@ -50,9 +50,6 @@ class EmscriptenGlueGenerator {
       Address staticBump, std::vector<Name> const& initializerFunctions,
       unsigned numReservedFunctionPointers);
 
-  // Replace placeholder emscripten_asm_const functions with *_signature versions.
-  void fixEmAsmConsts();
-
   void fixInvokeFunctionNames();
 
   void separateDataSegments(Output* outfile);

src/wasm/wasm-emscripten.cpp

@@ -44,6 +44,8 @@ void addExportedFunction(Module& wasm, Function* function) {
 
 Global* EmscriptenGlueGenerator::getStackPointerGlobal() {
   // Assumption: first global is __stack_pointer
+  // TODO(sbc): Once mutable globals are a thing we shouldn't need this
+  // at all since we can simply export __stack_pointer.
   return wasm.globals[0].get();
 }
 
@@ -308,9 +310,14 @@ void EmscriptenGlueGenerator::generateJSCallThunks(
 std::vector<Address> getSegmentOffsets(Module& wasm) {
   std::vector<Address> segmentOffsets;
   for (unsigned i = 0; i < wasm.memory.segments.size(); ++i) {
-    Const* addrConst = wasm.memory.segments[i].offset->cast<Const>();
-    auto address = addrConst->value.geti32();
-    segmentOffsets.push_back(address);
+    if (auto* addrConst = wasm.memory.segments[i].offset->dynCast<Const>()) {
+      auto address = addrConst->value.geti32();
+      segmentOffsets.push_back(address);
+    } else {
+      // TODO(sbc): Wasm shared libraries have data segments with non-const
+      // offset.
+      segmentOffsets.push_back(0);
+    }
   }
   return segmentOffsets;
 }
@@ -552,12 +559,6 @@ EmJsWalker fixEmJsFuncsAndReturnWalker(Module& wasm) {
   return walker;
 }
 
-void EmscriptenGlueGenerator::fixEmAsmConsts() {
-  fixEmAsmConstsAndReturnWalker(wasm);
-  fixEmJsFuncsAndReturnWalker(wasm);
-}
-
-
 // Fixes function name hacks caused by LLVM exception & setjmp/longjmp
 // handling pass for wasm.
 // This does two things: