3 files changed, 38 insertions, 2 deletions
diff --git a/src/s2wasm.h b/src/s2wasm.h
index 729e060f9..5614c7b58 100644
--- a/src/s2wasm.h
+++ b/src/s2wasm.h
@@ -639,6 +639,13 @@ class S2WasmBuilder {
         }
       } else if (match(".result")) {
         resultType = getType();
+      } else if (match(".indidx")) {
+        int64_t indirectIndex = getInt64();
+        skipWhitespace();
+        if (indirectIndex < 0) {
+          abort_on("indidx");
+        }
+        linkerObj->addIndirectIndex(name, indirectIndex);
       } else if (match(".local")) {
         while (1) {
           Name name = getNextId();
diff --git a/src/wasm-linker.cpp b/src/wasm-linker.cpp
index 628e24ecc..3ff90cc0a 100644
--- a/src/wasm-linker.cpp
+++ b/src/wasm-linker.cpp
@@ -112,9 +112,30 @@ void Linker::layout() {
   for (Name name : out.globls) exportFunction(name, false);
   for (Name name : out.initializerFunctions) exportFunction(name, true);
 
+  // Pre-assign the function indexes
+  for (auto& pair : out.indirectIndexes) {
+    if (functionIndexes.count(pair.first) != 0 ||
+        functionNames.count(pair.second) != 0) {
+      Fatal() << "Function " << pair.first << " already has an index " <<
+          functionIndexes[pair.first] << " while setting index " << pair.second;
+    }
+    if (debug) {
+      std::cerr << "pre-assigned function index: " << pair.first << ": "
+                << pair.second << '\n';
+    }
+    functionIndexes[pair.first] = pair.second;
+    functionNames[pair.second] = pair.first;
+  }
+
+  // Emit the pre-assigned function names in sorted order
+  for (const auto& P : functionNames) {
+    out.wasm.table.names.push_back(P.second);
+  }
+
   auto ensureFunctionIndex = [this](Name name) {
     if (functionIndexes.count(name) == 0) {
       functionIndexes[name] = out.wasm.table.names.size();
+      functionNames[functionIndexes[name]] = name;
       out.wasm.table.names.push_back(name);
       if (debug) {
         std::cerr << "function index: " << name << ": "
diff --git a/src/wasm-linker.h b/src/wasm-linker.h
index 535b5dc55..701585190 100644
--- a/src/wasm-linker.h
+++ b/src/wasm-linker.h
@@ -141,6 +141,11 @@ class LinkerObject {
     return f->second;
   }
 
+  void addIndirectIndex(Name name, Address index) {
+    assert(!indirectIndexes.count(name));
+    indirectIndexes[name] = index;
+  }
+
   bool isEmpty() {
     return wasm.functions.empty();
   }
@@ -173,6 +178,9 @@ class LinkerObject {
 
   std::map<Name, Address> segments; // name => segment index (in wasm module)
 
+  // preassigned indexes for functions called indirectly
+  std::map<Name, Address> indirectIndexes;
+
   std::vector<Name> initializerFunctions;
 
   LinkerObject(const LinkerObject&) = delete;
@@ -309,8 +317,8 @@ class Linker {
 
   std::unordered_map<cashew::IString, int32_t> staticAddresses; // name => address
   std::unordered_map<Address, Address> segmentsByAddress; // address => segment index
-  std::unordered_map<cashew::IString, size_t> functionIndexes;
-
+  std::unordered_map<cashew::IString, Address> functionIndexes;
+  std::map<Address, cashew::IString> functionNames;
 };