diff --git a/auto_update_tests.py b/auto_update_tests.py
index d76d087506e..c6d376fa043 100755
--- a/auto_update_tests.py
+++ b/auto_update_tests.py
@@ -41,6 +41,10 @@
         print ' '.join(cmd)
         actual = run_command(cmd)
         with open(os.path.join('test', wasm), 'w') as o: o.write(actual)
+        if 'debugInfo' in asm:
+          cmd += ['--source-map', os.path.join('test', wasm + '.map'), '-o', 'a.wasm']
+          run_command(cmd)
+
 
 for dot_s_dir in ['dot_s', 'llvm_autogenerated']:
   for s in sorted(os.listdir(os.path.join('test', dot_s_dir))):
diff --git a/check.py b/check.py
index 05c2d92a6e2..9d5b64f1824 100755
--- a/check.py
+++ b/check.py
@@ -189,6 +189,31 @@ def do_asm2wasm_test():
               fail_with_error('wasm interpreter error: ' + err) # failed to pretty-print
             fail_with_error('wasm interpreter error')
 
+        # verify debug info
+        if 'debugInfo' in asm:
+          jsmap = 'a.wasm.map'
+          cmd += ['--source-map', jsmap,
+                  '--source-map-url', 'http://example.org/' + jsmap,
+                  '-o', 'a.wasm']
+          run_command(cmd)
+          if not os.path.isfile(jsmap):
+            fail_with_error('Debug info map not created: %s' % jsmap)
+          with open(wasm + '.map', 'rb') as expected:
+            with open(jsmap, 'rb') as actual:
+              fail_if_not_identical(actual.read(), expected.read())
+          with open('a.wasm', 'rb') as binary:
+            url_section_name = bytearray([16]) + bytearray('sourceMappingURL')
+            payload = 'http://example.org/' + jsmap
+            assert len(payload) < 256, 'name too long'
+            url_section_contents = bytearray([len(payload)]) + bytearray(payload)
+            print url_section_name
+            binary_contents = bytearray(binary.read())
+            if url_section_name not in binary_contents:
+              fail_with_error('source map url section not found in binary')
+            if url_section_contents not in binary_contents[binary_contents.index(url_section_name):]:
+              fail_with_error('source map url not found in url section')
+
+
 print '\n[ checking asm2wasm binary reading/writing... ]\n'
 
 asmjs = os.path.join(options.binaryen_test, 'hello_world.asm.js')
@@ -241,6 +266,8 @@ def do_asm2wasm_test():
     print '..', t
     t = os.path.join(options.binaryen_test, t)
     cmd = WASM_DIS + [t]
+    if os.path.isfile(t + '.map'): cmd += ['--source-map', t + '.map']
+
     actual = run_command(cmd)
 
     with open(t + '.fromBinary') as f:
diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index 16e7c95e1e9..b8439bdbf8d 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -1382,13 +1382,13 @@ void Asm2WasmBuilder::processAsm(Ref ast) {
                 while (i < expressionStack.size()) {
                   exp = expressionStack[i];
                   if (debugLocations.count(exp) == 0) {
-                    debugLocations[exp] = { fileIndex, lineNumber };
+                    debugLocations[exp] = { fileIndex, lineNumber, 0 };
                     break;
                   }
                   i++;
                 }
               } else {
-                debugLocations[exp] = { fileIndex, lineNumber };
+                debugLocations[exp] = { fileIndex, lineNumber, 0 };
               }
               break;
             }
diff --git a/src/parsing.h b/src/parsing.h
index d4df3c1c25b..be3c112f3f0 100644
--- a/src/parsing.h
+++ b/src/parsing.h
@@ -193,6 +193,25 @@ struct ParseException {
   }
 };
 
+struct MapParseException {
+  std::string text;
+
+  MapParseException() : text("unknown parse error") {}
+  MapParseException(std::string text) : text(text) {}
+
+  void dump(std::ostream& o) {
+    Colors::magenta(o);
+    o << "[";
+    Colors::red(o);
+    o << "map parse exception: ";
+    Colors::green(o);
+    o << text;
+    Colors::magenta(o);
+    o << "]";
+    Colors::normal(o);
+  }
+};
+
 // Helper for parsers that may not have unique label names. This transforms
 // the names into unique ones, as required by Binaryen IR.
 struct UniqueNameMapper {
diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 6aebd612bc9..95f60e5e2c3 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -45,6 +45,7 @@ struct PrintSExpression : public Visitor<PrintSExpression> {
 
   Module* currModule = nullptr;
   Function* currFunction = nullptr;
+  Function::DebugLocation lastPrintedLocation;
 
   PrintSExpression(std::ostream& o) : o(o) {
     setMinify(false);
@@ -58,8 +59,11 @@ struct PrintSExpression : public Visitor<PrintSExpression> {
       auto iter = debugLocations.find(curr);
       if (iter != debugLocations.end()) {
         auto fileName = currModule->debugInfoFileNames[iter->second.fileIndex];
-        o << ";; " << fileName << ":" << iter->second.lineNumber << '\n';
-        doIndent(o, indent);
+        if (lastPrintedLocation != iter->second) {
+          lastPrintedLocation = iter->second;
+          o << ";;@ " << fileName << ":" << iter->second.lineNumber << ":" << iter->second.columnNumber << '\n';
+          doIndent(o, indent);
+        }
       }
     }
     Visitor<PrintSExpression>::visit(curr);
@@ -599,6 +603,7 @@ struct PrintSExpression : public Visitor<PrintSExpression> {
   }
   void visitFunction(Function *curr) {
     currFunction = curr;
+    lastPrintedLocation = { 0, 0, 0 };
     printOpening(o, "func ", true);
     printName(curr->name);
     if (curr->type.is()) {
diff --git a/src/s2wasm.h b/src/s2wasm.h
index 6ba4750ec49..efa4ad6013b 100644
--- a/src/s2wasm.h
+++ b/src/s2wasm.h
@@ -44,6 +44,7 @@ class S2WasmBuilder {
   MixedArena* allocator;
   LinkerObject* linkerObj;
   std::unique_ptr<LinkerObject::SymbolInfo> symbolInfo;
+  std::unordered_map<uint32_t, uint32_t> fileIndexMap;
 
  public:
   S2WasmBuilder(const char* input, bool debug)
@@ -601,7 +602,9 @@ class S2WasmBuilder {
       size_t fileId = getInt();
       skipWhitespace();
       auto quoted = getQuoted();
-      WASM_UNUSED(fileId); WASM_UNUSED(quoted); // TODO: use the fileId and quoted
+      uint32_t index = wasm->debugInfoFileNames.size();
+      fileIndexMap[fileId] = index;
+      wasm->debugInfoFileNames.push_back(std::string(quoted.begin(), quoted.end()));
       s = strchr(s, '\n');
       return;
     }
@@ -665,22 +668,31 @@ class S2WasmBuilder {
 
     mustMatch(":");
 
+    Function::DebugLocation debugLocation = { 0, 0, 0 };
+    bool useDebugLocation = false;
     auto recordFile = [&]() {
       if (debug) dump("file");
       size_t fileId = getInt();
       skipWhitespace();
       auto quoted = getQuoted();
-      WASM_UNUSED(fileId); WASM_UNUSED(quoted); // TODO: use the fileId and quoted
+      uint32_t index = wasm->debugInfoFileNames.size();
+      fileIndexMap[fileId] = index;
+      wasm->debugInfoFileNames.push_back(std::string(quoted.begin(), quoted.end()));
       s = strchr(s, '\n');
     };
     auto recordLoc = [&]() {
       if (debug) dump("loc");
       size_t fileId = getInt();
       skipWhitespace();
-      size_t row = getInt();
+      uint32_t row = getInt();
       skipWhitespace();
-      size_t column = getInt();
-      WASM_UNUSED(fileId); WASM_UNUSED(row); WASM_UNUSED(column); // TODO: use the fileId, row and column
+      uint32_t column = getInt();
+      auto iter = fileIndexMap.find(fileId);
+      if (iter == fileIndexMap.end()) {
+        abort_on("idx");
+      }
+      useDebugLocation = true;
+      debugLocation = { iter->second, row, column };
       s = strchr(s, '\n');
     };
     auto recordLabel = [&]() {
@@ -746,7 +758,10 @@ class S2WasmBuilder {
     // parse body
     func->body = allocator->alloc<Block>();
     std::vector<Expression*> bstack;
-    auto addToBlock = [&bstack](Expression* curr) {
+    auto addToBlock = [&](Expression* curr) {
+      if (useDebugLocation) {
+        func->debugLocations[curr] = debugLocation;
+      }
       Expression* last = bstack.back();
       if (last->is<Loop>()) {
         last = last->cast<Loop>()->body;
diff --git a/src/tools/asm2wasm.cpp b/src/tools/asm2wasm.cpp
index cf0715198ad..3fa97d9815b 100644
--- a/src/tools/asm2wasm.cpp
+++ b/src/tools/asm2wasm.cpp
@@ -36,6 +36,8 @@ int main(int argc, const char *argv[]) {
   bool legalizeJavaScriptFFI = true;
   Asm2WasmBuilder::TrapMode trapMode = Asm2WasmBuilder::TrapMode::JS;
   bool wasmOnly = false;
+  std::string sourceMapFilename;
+  std::string sourceMapUrl;
   std::string symbolMap;
   bool emitBinary = true;
 
@@ -99,9 +101,15 @@ int main(int argc, const char *argv[]) {
            [&legalizeJavaScriptFFI](Options *o, const std::string &) {
              legalizeJavaScriptFFI = false;
            })
-      .add("--debuginfo", "-g", "Emit names section and debug info (for debug info you must emit text, -S, for this to work)",
+      .add("--debuginfo", "-g", "Emit names section in wasm binary (or full debuginfo in wast)",
            Options::Arguments::Zero,
            [&](Options *o, const std::string &arguments) { options.passOptions.debugInfo = true; })
+      .add("--source-map", "-sm", "Emit source map (if using binary output) to the specified file",
+           Options::Arguments::One,
+           [&sourceMapFilename](Options *o, const std::string &argument) { sourceMapFilename = argument; })
+      .add("--source-map-url", "-su", "Use specified string as source map URL",
+           Options::Arguments::One,
+           [&sourceMapUrl](Options *o, const std::string &argument) { sourceMapUrl = argument; })
       .add("--symbolmap", "-s", "Emit a symbol map (indexes => names)",
            Options::Arguments::One,
            [&](Options *o, const std::string &argument) { symbolMap = argument; })
@@ -136,8 +144,9 @@ int main(int argc, const char *argv[]) {
   }
 
   Asm2WasmPreProcessor pre;
-  // wasm binaries can contain a names section, but not full debug info
-  pre.debugInfo = options.passOptions.debugInfo && !emitBinary;
+  // wasm binaries can contain a names section, but not full debug info --
+  // debug info is disabled if a map file is not specified with wasm binary
+  pre.debugInfo = options.passOptions.debugInfo && (!emitBinary || sourceMapFilename.size());
   auto input(
       read_file<std::vector<char>>(options.extra["infile"], Flags::Text, options.debug ? Flags::Debug : Flags::Release));
   char *start = pre.process(input.data());
@@ -204,6 +213,10 @@ int main(int argc, const char *argv[]) {
   writer.setDebugInfo(options.passOptions.debugInfo);
   writer.setSymbolMap(symbolMap);
   writer.setBinary(emitBinary);
+  if (emitBinary) {
+    writer.setSourceMapFilename(sourceMapFilename);
+    writer.setSourceMapUrl(sourceMapUrl);
+  }
   writer.write(wasm, options.extra["output"]);
 
   if (options.debug) std::cerr << "done." << std::endl;
diff --git a/src/tools/wasm-as.cpp b/src/tools/wasm-as.cpp
index 067c0f28df6..e8003a5ca16 100644
--- a/src/tools/wasm-as.cpp
+++ b/src/tools/wasm-as.cpp
@@ -30,6 +30,8 @@ using namespace wasm;
 int main(int argc, const char *argv[]) {
   bool debugInfo = false;
   std::string symbolMap;
+  std::string sourceMapFilename;
+  std::string sourceMapUrl;
   Options options("wasm-as", "Assemble a .wast (WebAssembly text format) into a .wasm (WebAssembly binary format)");
   options.extra["validate"] = "wasm";
   options
@@ -51,6 +53,12 @@ int main(int argc, const char *argv[]) {
       .add("--debuginfo", "-g", "Emit names section and debug info",
            Options::Arguments::Zero,
            [&](Options *o, const std::string &arguments) { debugInfo = true; })
+      .add("--source-map", "-sm", "Emit source map to the specified file",
+           Options::Arguments::One,
+           [&sourceMapFilename](Options *o, const std::string &argument) { sourceMapFilename = argument; })
+      .add("--source-map-url", "-su", "Use specified string as source map URL",
+           Options::Arguments::One,
+           [&sourceMapUrl](Options *o, const std::string &argument) { sourceMapUrl = argument; })
       .add("--symbolmap", "-s", "Emit a symbol map (indexes => names)",
            Options::Arguments::One,
            [&](Options *o, const std::string &argument) { symbolMap = argument; })
@@ -86,13 +94,23 @@ int main(int argc, const char *argv[]) {
   if (options.debug) std::cerr << "binarification..." << std::endl;
   BufferWithRandomAccess buffer(options.debug);
   WasmBinaryWriter writer(&wasm, buffer, options.debug);
-  writer.setDebugInfo(debugInfo);
+  // if debug info is used, then we want to emit the names section
+  writer.setNamesSection(debugInfo);
+  std::unique_ptr<std::ofstream> sourceMapStream = nullptr;
+  if (sourceMapFilename.size()) {
+    sourceMapStream = make_unique<std::ofstream>();
+    sourceMapStream->open(sourceMapFilename);
+    writer.setSourceMap(sourceMapStream.get(), sourceMapUrl);
+  }
   if (symbolMap.size() > 0) writer.setSymbolMap(symbolMap);
   writer.write();
 
   if (options.debug) std::cerr << "writing to output..." << std::endl;
   Output output(options.extra["output"], Flags::Binary, options.debug ? Flags::Debug : Flags::Release);
   buffer.writeTo(output);
+  if (sourceMapStream) {
+    sourceMapStream->close();
+  }
 
   if (options.debug) std::cerr << "Done." << std::endl;
 }
diff --git a/src/tools/wasm-dis.cpp b/src/tools/wasm-dis.cpp
index 93c28691362..e6fd7baddf9 100644
--- a/src/tools/wasm-dis.cpp
+++ b/src/tools/wasm-dis.cpp
@@ -28,6 +28,7 @@ using namespace cashew;
 using namespace wasm;
 
 int main(int argc, const char *argv[]) {
+  std::string sourceMapFilename;
   Options options("wasm-dis", "Un-assemble a .wasm (WebAssembly binary format) into a .wast (WebAssembly text format)");
   options.add("--output", "-o", "Output file (stdout if not specified)",
               Options::Arguments::One,
@@ -35,6 +36,9 @@ int main(int argc, const char *argv[]) {
                 o->extra["output"] = argument;
                 Colors::disable();
               })
+      .add("--source-map", "-sm", "Consume source map from the specified file to add location information",
+           Options::Arguments::One,
+           [&sourceMapFilename](Options *o, const std::string &argument) { sourceMapFilename = argument; })
       .add_positional("INFILE", Options::Arguments::One,
                       [](Options *o, const std::string &argument) {
                         o->extra["infile"] = argument;
@@ -46,11 +50,23 @@ int main(int argc, const char *argv[]) {
   if (options.debug) std::cerr << "parsing binary..." << std::endl;
   Module wasm;
   try {
+    std::unique_ptr<std::ifstream> sourceMapStream;
     WasmBinaryBuilder parser(wasm, input, options.debug);
+    if (sourceMapFilename.size()) {
+        sourceMapStream = make_unique<std::ifstream>();
+        sourceMapStream->open(sourceMapFilename);
+        parser.setDebugLocations(sourceMapStream.get());
+    }
     parser.read();
+    if (sourceMapStream) {
+        sourceMapStream->close();
+    }
   } catch (ParseException& p) {
     p.dump(std::cerr);
     Fatal() << "error in parsing wasm binary";
+  } catch (MapParseException& p) {
+    p.dump(std::cerr);
+    Fatal() << "error in parsing wasm source mapping";
   }
 
   if (options.debug) std::cerr << "Printing..." << std::endl;
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 921f90ac8b5..889a3aa6c90 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -308,6 +308,7 @@ enum EncodedType {
 
 namespace UserSections {
 extern const char* Name;
+extern const char* SourceMapUrl;
 
 enum Subsection {
   NameFunction = 1,
@@ -534,8 +535,11 @@ inline S32LEB binaryWasmType(WasmType type) {
 class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
   Module* wasm;
   BufferWithRandomAccess& o;
+  Function* currFunction = nullptr;
   bool debug;
   bool debugInfo = true;
+  std::ostream* sourceMap = nullptr;
+  std::string sourceMapUrl;
   std::string symbolMap;
 
   MixedArena allocator;
@@ -546,7 +550,11 @@ class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
     prepare();
   }
 
-  void setDebugInfo(bool set) { debugInfo = set; }
+  void setNamesSection(bool set) { debugInfo = set; }
+  void setSourceMap(std::ostream* set, std::string url) {
+    sourceMap = set;
+    sourceMapUrl = url;
+  }
   void setSymbolMap(std::string set) { symbolMap = set; }
 
   void write();
@@ -582,8 +590,13 @@ class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
   void writeFunctionTableDeclaration();
   void writeTableElements();
   void writeNames();
+  void writeSourceMapUrl();
   void writeSymbolMap();
 
+  void writeSourceMapProlog();
+  void writeSourceMapEpilog();
+  void writeDebugLocation(size_t offset, const Function::DebugLocation& loc);
+
   // helpers
   void writeInlineString(const char* name);
   void writeInlineBuffer(const char* data, size_t size);
@@ -606,6 +619,20 @@ class WasmBinaryWriter : public Visitor<WasmBinaryWriter, void> {
 
   void recurse(Expression*& curr);
   std::vector<Name> breakStack;
+  Function::DebugLocation lastDebugLocation;
+  size_t lastBytecodeOffset;
+
+  void visit(Expression* curr) {
+    if (sourceMap && currFunction) {
+      // Dump the sourceMap debug info
+      auto& debugLocations = currFunction->debugLocations;
+      auto iter = debugLocations.find(curr);
+      if (iter != debugLocations.end() && iter->second != lastDebugLocation) {
+        writeDebugLocation(o.size(), iter->second);
+      }
+    }
+    Visitor<WasmBinaryWriter>::visit(curr);
+  }
 
   void visitBlock(Block *curr);
   // emits a node, but if it is a block with no name, emit a list of its contents
@@ -641,14 +668,17 @@ class WasmBinaryBuilder {
   MixedArena& allocator;
   std::vector<char>& input;
   bool debug;
+  std::istream* sourceMap;
+  std::pair<uint32_t, Function::DebugLocation> nextDebugLocation;
 
   size_t pos = 0;
   Index startIndex = -1;
+  bool useDebugLocation;
 
   std::set<BinaryConsts::Section> seenSections;
 
 public:
-  WasmBinaryBuilder(Module& wasm, std::vector<char>& input, bool debug) : wasm(wasm), allocator(wasm.allocator), input(input), debug(debug) {}
+  WasmBinaryBuilder(Module& wasm, std::vector<char>& input, bool debug) : wasm(wasm), allocator(wasm.allocator), input(input), debug(debug), sourceMap(nullptr), nextDebugLocation(0, { 0, 0, 0 }), useDebugLocation(false) {}
 
   void read();
   void readUserSection(size_t payloadLen);
@@ -737,6 +767,15 @@ class WasmBinaryBuilder {
   void readTableElements();
   void readNames(size_t);
 
+  // Debug information reading helpers
+  void setDebugLocations(std::istream* sourceMap_) {
+      sourceMap = sourceMap_;
+  }
+  Function::DebugLocation debugLocation;
+  std::unordered_map<std::string, Index> debugInfoFileIndices;
+  void readNextDebugLocation();
+  void readSourceMapHeader();
+
   // AST reading
   int depth = 0; // only for debugging
 
diff --git a/src/wasm-io.h b/src/wasm-io.h
index 803cbaf90c3..afdc4503ce2 100644
--- a/src/wasm-io.h
+++ b/src/wasm-io.h
@@ -48,11 +48,15 @@ class ModuleWriter : public ModuleIO {
   bool binary = true;
   bool debugInfo = false;
   std::string symbolMap;
+  std::string sourceMapFilename;
+  std::string sourceMapUrl;
 
 public:
   void setBinary(bool binary_) { binary = binary_; }
   void setDebugInfo(bool debugInfo_) { debugInfo = debugInfo_; }
   void setSymbolMap(std::string symbolMap_) { symbolMap = symbolMap_; }
+  void setSourceMapFilename(std::string sourceMapFilename_) { sourceMapFilename = sourceMapFilename_; }
+  void setSourceMapUrl(std::string sourceMapUrl_) { sourceMapUrl = sourceMapUrl_; }
 
   // write text
   void writeText(Module& wasm, std::string filename);
diff --git a/src/wasm-s-parser.h b/src/wasm-s-parser.h
index be1f6b6999f..b02b6523bcd 100644
--- a/src/wasm-s-parser.h
+++ b/src/wasm-s-parser.h
@@ -28,6 +28,16 @@
 
 namespace wasm {
 
+class SourceLocation
+{
+public:
+  cashew::IString filename;
+  uint32_t line;
+  uint32_t column;
+  SourceLocation(cashew::IString filename_, uint32_t line_, uint32_t column_ = 0)
+   : filename(filename_), line(line_), column(column_) {}
+};
+
 //
 // An element in an S-Expression: a list or a string
 //
@@ -41,7 +51,7 @@ class Element {
   bool quoted_;
 
 public:
-  Element(MixedArena& allocator) : isList_(true), list_(allocator), line(-1), col(-1) {}
+  Element(MixedArena& allocator) : isList_(true), list_(allocator), line(-1), col(-1), loc(nullptr) {}
 
   bool isList() { return isList_; }
   bool isStr() { return !isList_; }
@@ -49,6 +59,7 @@ class Element {
   bool quoted() { return isStr() && quoted_; }
 
   size_t line, col;
+  SourceLocation* loc;
 
   // list methods
   List& list();
@@ -61,14 +72,13 @@ class Element {
   cashew::IString str();
   const char* c_str();
   Element* setString(cashew::IString str__, bool dollared__, bool quoted__);
-  Element* setMetadata(size_t line_, size_t col_);
+  Element* setMetadata(size_t line_, size_t col_, SourceLocation* loc_);
 
   // printing
   friend std::ostream& operator<<(std::ostream& o, Element& e);
   void dump();
 };
 
-
 //
 // Generic S-Expression parsing into lists
 //
@@ -76,6 +86,7 @@ class SExpressionParser {
   char* input;
   size_t line;
   char* lineStart;
+  SourceLocation* loc;
 
   MixedArena allocator;
 
@@ -87,6 +98,7 @@ class SExpressionParser {
 private:
   Element* parse();
   void skipWhitespace();
+  void parseDebugLocation();
   Element* parseString();
 };
 
@@ -102,6 +114,7 @@ class SExpressionWasmBuilder {
   int functionCounter;
   int globalCounter;
   std::map<Name, WasmType> functionTypes; // we need to know function return types before we parse their contents
+  std::unordered_map<cashew::IString, Index> debugInfoFileIndices;
 
 public:
   // Assumes control of and modifies the input.
@@ -147,6 +160,7 @@ class SExpressionWasmBuilder {
   Expression* parseExpression(Element& s);
 
 private:
+  Expression* makeExpression(Element& s);
   Expression* makeBinary(Element& s, BinaryOp op, WasmType type);
   Expression* makeUnary(Element& s, UnaryOp op, WasmType type);
   Expression* makeSelect(Element& s);
diff --git a/src/wasm.h b/src/wasm.h
index 3caab9dbc52..dba08d92ead 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -527,7 +527,9 @@ class Function {
   std::map<Name, Index> localIndices;
 
   struct DebugLocation {
-    uint32_t fileIndex, lineNumber;
+    uint32_t fileIndex, lineNumber, columnNumber;
+    bool operator==(const DebugLocation& other) const { return fileIndex == other.fileIndex && lineNumber == other.lineNumber && columnNumber == other.columnNumber; }
+    bool operator!=(const DebugLocation& other) const { return !(*this == other); }
   };
   std::unordered_map<Expression*, DebugLocation> debugLocations;
 
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 65c6f2a2157..c4bc66f7681 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -33,6 +33,9 @@ void WasmBinaryWriter::prepare() {
 
 void WasmBinaryWriter::write() {
   writeHeader();
+  if (sourceMap) {
+    writeSourceMapProlog();
+  }
 
   writeTypes();
   writeImports();
@@ -46,8 +49,12 @@ void WasmBinaryWriter::write() {
   writeFunctions();
   writeDataSegments();
   if (debugInfo) writeNames();
+  if (sourceMap) writeSourceMapUrl();
   if (symbolMap.size() > 0) writeSymbolMap();
 
+  if (sourceMap) {
+    writeSourceMapEpilog();
+  }
   finishUp();
 }
 
@@ -236,6 +243,7 @@ void WasmBinaryWriter::writeFunctions() {
     size_t sizePos = writeU32LEBPlaceholder();
     size_t start = o.size();
     Function* function = wasm->functions[i].get();
+    currFunction = function;
     mappedLocals.clear();
     numLocalsByType.clear();
     if (debug) std::cerr << "writing" << function->name << std::endl;
@@ -258,6 +266,7 @@ void WasmBinaryWriter::writeFunctions() {
     if (debug) std::cerr << "body size: " << size << ", writing at " << sizePos << ", next starts at " << o.size() << std::endl;
     o.writeAt(sizePos, U32LEB(size));
   }
+  currFunction = nullptr;
   finishSection(start);
 }
 
@@ -420,6 +429,14 @@ void WasmBinaryWriter::writeNames() {
   finishSection(start);
 }
 
+void WasmBinaryWriter::writeSourceMapUrl() {
+  if (debug) std::cerr << "== writeSourceMapUrl" << std::endl;
+  auto start = startSection(BinaryConsts::Section::User);
+  writeInlineString(BinaryConsts::UserSections::SourceMapUrl);
+  writeInlineString(sourceMapUrl.c_str());
+  finishSection(start);
+}
+
 void WasmBinaryWriter::writeSymbolMap() {
   std::ofstream file(symbolMap);
   for (auto& import : wasm->imports) {
@@ -433,6 +450,50 @@ void WasmBinaryWriter::writeSymbolMap() {
   file.close();
 }
 
+void WasmBinaryWriter::writeSourceMapProlog() {
+  lastDebugLocation = { 0, /* lineNumber = */ 1, 0 };
+  lastBytecodeOffset = 0;
+  *sourceMap << "{\"version\":3,\"sources\":[";
+  for (size_t i = 0; i < wasm->debugInfoFileNames.size(); i++) {
+    if (i > 0) *sourceMap << ",";
+    // TODO respect JSON string encoding, e.g. quotes and control chars.
+    *sourceMap << "\"" << wasm->debugInfoFileNames[i] << "\"";
+  }
+  *sourceMap << "],\"names\":[],\"mappings\":\"";
+}
+
+void WasmBinaryWriter::writeSourceMapEpilog() {
+  *sourceMap << "\"}";
+}
+
+static void writeBase64VLQ(std::ostream& out, int32_t n) {
+  uint32_t value = n >= 0 ? n << 1 : ((-n) << 1) | 1;
+  while (1) {
+    uint32_t digit = value & 0x1F;
+    value >>= 5;
+    if (!value) {
+      // last VLQ digit -- base64 codes 'A'..'Z', 'a'..'f'
+      out << char(digit < 26 ? 'A' + digit : 'a' + digit - 26);
+      break;
+    }
+    // more VLG digit will follow -- add continuation bit (0x20),
+    // base64 codes 'g'..'z', '0'..'9', '+', '/'
+    out << char(digit < 20 ? 'g' + digit : digit < 30 ? '0' + digit - 20 : digit == 30 ? '+' : '/');
+  }
+}
+
+void WasmBinaryWriter::writeDebugLocation(size_t offset, const Function::DebugLocation& loc) {
+  if (lastBytecodeOffset > 0) {
+    *sourceMap << ",";
+  }
+  writeBase64VLQ(*sourceMap, int32_t(offset - lastBytecodeOffset));
+  writeBase64VLQ(*sourceMap, int32_t(loc.fileIndex - lastDebugLocation.fileIndex));
+  writeBase64VLQ(*sourceMap, int32_t(loc.lineNumber - lastDebugLocation.lineNumber));
+  writeBase64VLQ(*sourceMap, int32_t(loc.columnNumber - lastDebugLocation.columnNumber));
+  lastDebugLocation = loc;
+  lastBytecodeOffset = offset;
+}
+
 void WasmBinaryWriter::writeInlineString(const char* name) {
   int32_t size = strlen(name);
   o << U32LEB(size);
@@ -937,6 +998,7 @@ static Name RETURN_BREAK("binaryen|break-to-return");
 void WasmBinaryBuilder::read() {
 
   readHeader();
+  readSourceMapHeader();
 
   // read sections until the end
   while (more()) {
@@ -1342,6 +1404,7 @@ void WasmBinaryBuilder::readFunctions() {
       // process the function body
       if (debug) std::cerr << "processing function: " << i << std::endl;
       nextLabel = 0;
+      useDebugLocation = false;
       breaksToReturn = false;
       // process body
       assert(breakStack.empty());
@@ -1389,6 +1452,136 @@ void WasmBinaryBuilder::readExports() {
   }
 }
 
+static int32_t readBase64VLQ(std::istream& in) {
+  uint32_t value = 0;
+  uint32_t shift = 0;
+  while (1) {
+    char ch = in.get();
+    if (ch == EOF)
+      throw MapParseException("unexpected EOF in the middle of VLQ");
+    if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch < 'g')) {
+      // last number digit
+      uint32_t digit = ch < 'a' ? ch - 'A' : ch - 'a' + 26;
+      value |= digit << shift;
+      break;
+    }
+    if (!(ch >= 'g' && ch <= 'z') && !(ch >= '0' && ch <= '9') &&
+        ch != '+' && ch != '/') {
+      throw MapParseException("invalid VLQ digit");
+    }
+    uint32_t digit = ch > '9' ? ch - 'g' : (ch >= '0' ? ch - '0' + 20 : (ch == '+' ? 30 : 31));
+    value |= digit << shift;
+    shift += 5;
+  }
+  return value & 1 ? -int32_t(value >> 1) : int32_t(value >> 1);
+}
+
+void WasmBinaryBuilder::readSourceMapHeader() {
+  if (!sourceMap) return;
+
+  auto maybeReadChar = [&](char expected) {
+    if (sourceMap->peek() != expected) return false;
+    sourceMap->get();
+    return true;
+  };
+  auto mustReadChar = [&](char expected) {
+    if (sourceMap->get() != expected) {
+      throw MapParseException("Unexpected char");
+    }
+  };
+  auto findField = [&](const char* name, size_t len) {
+    bool matching = false;
+    size_t pos;
+    while (1) {
+      int ch = sourceMap->get();
+      if (ch == EOF) return false;
+      if (ch == '\"') {
+        matching = true;
+        pos = 0;
+      } else if (matching && name[pos] == ch) {
+        ++pos;
+        if (pos == len) {
+          if (maybeReadChar('\"')) break; // found field
+        }
+      } else {
+        matching = false;
+      }
+    }
+    mustReadChar(':');
+    return true;
+  };
+  auto readString = [&](std::string& str) {
+    std::vector<char> vec;
+    mustReadChar('\"');
+    if (!maybeReadChar('\"')) {
+      while (1) {
+        int ch = sourceMap->get();
+        if (ch == EOF) {
+          throw MapParseException("unexpected EOF in the middle of string");
+        }
+        if (ch == '\"') break;
+        vec.push_back(ch);
+      }
+    }
+    str = std::string(vec.begin(), vec.end());
+  };
+
+  if (!findField("sources", strlen("sources"))) {
+    throw MapParseException("cannot find the sources field in map");
+  }
+  mustReadChar('[');
+  if (!maybeReadChar(']')) {
+    do {
+      std::string file;
+      readString(file);
+      Index index = wasm.debugInfoFileNames.size();
+      wasm.debugInfoFileNames.push_back(file);
+      debugInfoFileIndices[file] = index;
+    } while (maybeReadChar(','));
+    mustReadChar(']');
+  }
+
+  if (!findField("mappings", strlen("mappings"))) {
+    throw MapParseException("cannot find the mappings field in map");
+  }
+  mustReadChar('\"');
+  if (maybeReadChar('\"')) { // empty mappings
+    nextDebugLocation.first = 0;
+    return;
+  }
+  // read first debug location
+  uint32_t position = readBase64VLQ(*sourceMap);
+  uint32_t fileIndex = readBase64VLQ(*sourceMap);
+  uint32_t lineNumber = readBase64VLQ(*sourceMap) + 1; // adjust zero-based line number
+  uint32_t columnNumber = readBase64VLQ(*sourceMap);
+  nextDebugLocation = { position, { fileIndex, lineNumber, columnNumber } };
+}
+
+void WasmBinaryBuilder::readNextDebugLocation() {
+  if (!sourceMap) return;
+
+  char ch;
+  *sourceMap >> ch;
+  if (ch == '\"') { // end of records
+    nextDebugLocation.first = 0;
+    return;
+  }
+  if (ch != ',') {
+    throw MapParseException("Unexpected delimiter");
+  }
+
+  int32_t positionDelta = readBase64VLQ(*sourceMap);
+  uint32_t position = nextDebugLocation.first + positionDelta;
+  int32_t fileIndexDelta = readBase64VLQ(*sourceMap);
+  uint32_t fileIndex = nextDebugLocation.second.fileIndex + fileIndexDelta;
+  int32_t lineNumberDelta = readBase64VLQ(*sourceMap);
+  uint32_t lineNumber = nextDebugLocation.second.lineNumber + lineNumberDelta;
+  int32_t columnNumberDelta = readBase64VLQ(*sourceMap);
+  uint32_t columnNumber = nextDebugLocation.second.columnNumber + columnNumberDelta;
+
+  nextDebugLocation = { position, { fileIndex, lineNumber, columnNumber } };
+}
+
 Expression* WasmBinaryBuilder::readExpression() {
   assert(depth == 0);
   processExpressions();
@@ -1627,6 +1820,16 @@ BinaryConsts::ASTNodes WasmBinaryBuilder::readExpression(Expression*& curr) {
     throw ParseException("Reached function end without seeing End opcode");
   }
   if (debug) std::cerr << "zz recurse into " << ++depth << " at " << pos << std::endl;
+  if (nextDebugLocation.first) {
+    while (nextDebugLocation.first && nextDebugLocation.first <= pos) {
+      if (nextDebugLocation.first < pos) {
+        std::cerr << "skipping debug location info for " << nextDebugLocation.first << std::endl;
+      }
+      debugLocation = nextDebugLocation.second;
+      useDebugLocation = currFunction; // using only for function expressions
+      readNextDebugLocation();
+    }
+  }
   uint8_t code = getInt8();
   if (debug) std::cerr << "readExpression seeing " << (int)code << std::endl;
   switch (code) {
@@ -1661,6 +1864,9 @@ BinaryConsts::ASTNodes WasmBinaryBuilder::readExpression(Expression*& curr) {
       throw ParseException("bad node code " + std::to_string(code));
     }
   }
+  if (useDebugLocation && curr) {
+    currFunction->debugLocations[curr] = debugLocation;
+  }
   if (debug) std::cerr << "zz recurse from " << depth-- << " at " << pos << std::endl;
   return BinaryConsts::ASTNodes(code);
 }
diff --git a/src/wasm/wasm-io.cpp b/src/wasm/wasm-io.cpp
index c3192efbf91..ebc9af8deba 100644
--- a/src/wasm/wasm-io.cpp
+++ b/src/wasm/wasm-io.cpp
@@ -72,11 +72,21 @@ void ModuleWriter::writeBinary(Module& wasm, std::string filename) {
   if (debug) std::cerr << "writing binary to " << filename << "\n";
   BufferWithRandomAccess buffer(debug);
   WasmBinaryWriter writer(&wasm, buffer, debug);
-  writer.setDebugInfo(debugInfo);
+  // if debug info is used, then we want to emit the names section
+  writer.setNamesSection(debugInfo);
+  std::unique_ptr<std::ofstream> sourceMapStream;
+  if (sourceMapFilename.size()) {
+    sourceMapStream = make_unique<std::ofstream>();
+    sourceMapStream->open(sourceMapFilename);
+    writer.setSourceMap(sourceMapStream.get(), sourceMapUrl);
+  }
   if (symbolMap.size() > 0) writer.setSymbolMap(symbolMap);
   writer.write();
   Output output(filename, Flags::Binary, debug ? Flags::Debug : Flags::Release);
   buffer.writeTo(output);
+  if (sourceMapStream) {
+    sourceMapStream->close();
+  }
 }
 
 void ModuleWriter::write(Module& wasm, std::string filename) {
@@ -88,4 +98,3 @@ void ModuleWriter::write(Module& wasm, std::string filename) {
 }
 
 }
-
diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index 9b053d5b8ce..1842237a579 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -71,9 +71,10 @@ Element* Element::setString(IString str__, bool dollared__, bool quoted__) {
   return this;
 }
 
-Element* Element::setMetadata(size_t line_, size_t col_) {
+Element* Element::setMetadata(size_t line_, size_t col_, SourceLocation* loc_) {
   line = line_;
   col = col_;
+  loc = loc_;
   return this;
 }
 
@@ -93,7 +94,7 @@ void Element::dump() {
 }
 
 
-SExpressionParser::SExpressionParser(char* input) : input(input) {
+SExpressionParser::SExpressionParser(char* input) : input(input), loc(nullptr) {
   root = nullptr;
   line = 1;
   lineStart = input;
@@ -104,6 +105,7 @@ SExpressionParser::SExpressionParser(char* input) : input(input) {
 
 Element* SExpressionParser::parse() {
   std::vector<Element *> stack;
+  std::vector<SourceLocation*> stackLocs;
   Element *curr = allocator.alloc<Element>();
   while (1) {
     skipWhitespace();
@@ -111,7 +113,9 @@ Element* SExpressionParser::parse() {
     if (input[0] == '(') {
       input++;
       stack.push_back(curr);
-      curr = allocator.alloc<Element>()->setMetadata(line, input - lineStart - 1);
+      curr = allocator.alloc<Element>()->setMetadata(line, input - lineStart - 1, loc);
+      stackLocs.push_back(loc);
+      assert(stack.size() == stackLocs.size());
     } else if (input[0] == ')') {
       input++;
       auto last = curr;
@@ -119,7 +123,10 @@ Element* SExpressionParser::parse() {
         throw ParseException("s-expr stack empty");
       }
       curr = stack.back();
+      assert(stack.size() == stackLocs.size());
       stack.pop_back();
+      loc = stackLocs.back();
+      stackLocs.pop_back();
       curr->list().push_back(last);
     } else {
       curr->list().push_back(parseString());
@@ -129,6 +136,29 @@ Element* SExpressionParser::parse() {
   return curr;
 }
 
+void SExpressionParser::parseDebugLocation() {
+  // Extracting debug location (if valid)
+  char* debugLoc = input + 3; // skipping ";;@"
+  while (debugLoc[0] && debugLoc[0] == ' ') debugLoc++;
+  char* debugLocEnd = debugLoc;
+  while (debugLocEnd[0] && debugLocEnd[0] != '\n') debugLocEnd++;
+  char* pos = debugLoc;
+  while (pos < debugLocEnd && pos[0] != ':') pos++;
+  if (pos >= debugLocEnd) {
+    return; // no line number
+  }
+  std::string name(debugLoc, pos);
+  char* lineStart = ++pos;
+  while (pos < debugLocEnd && pos[0] != ':') pos++;
+  std::string lineStr(lineStart, pos);
+  if (pos >= debugLocEnd) {
+    return; // no column number
+  }
+  std::string colStr(++pos, debugLocEnd);
+  void* buf = allocator.allocSpace(sizeof(SourceLocation));
+  loc = new (buf) SourceLocation(IString(name.c_str(), false), atoi(lineStr.c_str()), atoi(colStr.c_str()));
+}
+
 void SExpressionParser::skipWhitespace() {
   while (1) {
     while (isspace(input[0])) {
@@ -139,6 +169,9 @@ void SExpressionParser::skipWhitespace() {
       input++;
     }
     if (input[0] == ';' && input[1] == ';') {
+      if (input[2] == '@') {
+        parseDebugLocation();
+      }
       while (input[0] && input[0] != '\n') input++;
       line++;
       lineStart = ++input;
@@ -198,13 +231,13 @@ Element* SExpressionParser::parseString() {
       input++;
     }
     input++;
-    return allocator.alloc<Element>()->setString(IString(str.c_str(), false), dollared, true)->setMetadata(line, start - lineStart);
+    return allocator.alloc<Element>()->setString(IString(str.c_str(), false), dollared, true)->setMetadata(line, start - lineStart, loc);
   }
   while (input[0] && !isspace(input[0]) && input[0] != ')' && input[0] != '(' && input[0] != ';') input++;
   if (start == input) throw ParseException("expected string", line, input - lineStart);
   char temp = input[0];
   input[0] = 0;
-  auto ret = allocator.alloc<Element>()->setString(IString(start, false), dollared, false)->setMetadata(line, start - lineStart);
+  auto ret = allocator.alloc<Element>()->setString(IString(start, false), dollared, false)->setMetadata(line, start - lineStart, loc);
   input[0] = temp;
   return ret;
 }
@@ -583,6 +616,23 @@ WasmType SExpressionWasmBuilder::stringToWasmType(const char* str, bool allowErr
 }
 
 Expression* SExpressionWasmBuilder::parseExpression(Element& s) {
+  Expression* result = makeExpression(s);
+  if (s.loc) {
+    IString file = s.loc->filename;
+    auto& debugInfoFileNames = wasm.debugInfoFileNames;
+    auto iter = debugInfoFileIndices.find(file);
+    if (iter == debugInfoFileIndices.end()) {
+      Index index = debugInfoFileNames.size();
+      debugInfoFileNames.push_back(file.c_str());
+      debugInfoFileIndices[file] = index;
+    }
+    uint32_t fileIndex = debugInfoFileIndices[file];
+    currFunction->debugLocations[result] = {fileIndex, s.loc->line, s.loc->column};
+  }
+  return result;
+}
+
+Expression* SExpressionWasmBuilder::makeExpression(Element& s) {
   IString id = s[0]->str();
   const char *str = id.str;
   const char *dot = strchr(str, '.');
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index 834d9e28f54..d2bf4e75cad 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -28,6 +28,7 @@ Name WASM("wasm"),
 namespace BinaryConsts {
 namespace UserSections {
 const char* Name = "name";
+const char* SourceMapUrl = "sourceMappingURL";
 }
 }
 
diff --git a/test/debugInfo.fromasm b/test/debugInfo.fromasm
index 84fb4aece99..7aa584c4371 100644
--- a/test/debugInfo.fromasm
+++ b/test/debugInfo.fromasm
@@ -11,21 +11,21 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $0 i32) (param $1 i32) (result i32)
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (i32.add
    (get_local $1)
    (get_local $1)
   )
  )
  (func $ret (param $0 i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $0
    (i32.shl
     (get_local $0)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (i32.add
    (get_local $0)
    (i32.const 1)
@@ -42,21 +42,21 @@
   )
  )
  (func $opts (param $0 i32) (param $1 i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $0
    (i32.add
     (get_local $0)
     (get_local $1)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $1
    (i32.shr_s
     (get_local $1)
     (get_local $0)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (i32.add
    (call $i32s-rem
     (get_local $0)
@@ -71,7 +71,7 @@
   (local $3 i32)
   (local $4 i32)
   (if
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (i32.gt_s
     (get_local $0)
     (i32.const 0)
@@ -91,21 +91,21 @@
     (set_local $1
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $1)
     )
    )
   )
   (loop $while-in
-   ;; fib.c:4
+   ;;@ fib.c:4:0
    (set_local $1
     (i32.add
      (get_local $3)
      (get_local $4)
     )
    )
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (set_local $2
     (i32.add
      (get_local $2)
@@ -113,7 +113,6 @@
     )
    )
    (if
-    ;; fib.c:3
     (i32.ne
      (get_local $2)
      (get_local $0)
@@ -129,7 +128,7 @@
     )
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (get_local $1)
  )
  (func $switch_reach (param $0 i32) (result i32)
@@ -189,7 +188,7 @@
     (get_local $0)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (get_local $1)
  )
 )
diff --git a/test/debugInfo.fromasm.clamp b/test/debugInfo.fromasm.clamp
index 84fb4aece99..7aa584c4371 100644
--- a/test/debugInfo.fromasm.clamp
+++ b/test/debugInfo.fromasm.clamp
@@ -11,21 +11,21 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $0 i32) (param $1 i32) (result i32)
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (i32.add
    (get_local $1)
    (get_local $1)
   )
  )
  (func $ret (param $0 i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $0
    (i32.shl
     (get_local $0)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (i32.add
    (get_local $0)
    (i32.const 1)
@@ -42,21 +42,21 @@
   )
  )
  (func $opts (param $0 i32) (param $1 i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $0
    (i32.add
     (get_local $0)
     (get_local $1)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $1
    (i32.shr_s
     (get_local $1)
     (get_local $0)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (i32.add
    (call $i32s-rem
     (get_local $0)
@@ -71,7 +71,7 @@
   (local $3 i32)
   (local $4 i32)
   (if
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (i32.gt_s
     (get_local $0)
     (i32.const 0)
@@ -91,21 +91,21 @@
     (set_local $1
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $1)
     )
    )
   )
   (loop $while-in
-   ;; fib.c:4
+   ;;@ fib.c:4:0
    (set_local $1
     (i32.add
      (get_local $3)
      (get_local $4)
     )
    )
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (set_local $2
     (i32.add
      (get_local $2)
@@ -113,7 +113,6 @@
     )
    )
    (if
-    ;; fib.c:3
     (i32.ne
      (get_local $2)
      (get_local $0)
@@ -129,7 +128,7 @@
     )
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (get_local $1)
  )
  (func $switch_reach (param $0 i32) (result i32)
@@ -189,7 +188,7 @@
     (get_local $0)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (get_local $1)
  )
 )
diff --git a/test/debugInfo.fromasm.clamp.map b/test/debugInfo.fromasm.clamp.map
new file mode 100644
index 00000000000..5680294cda5
--- /dev/null
+++ b/test/debugInfo.fromasm.clamp.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"yLC8ylTA,cC7vlTA,OAkDA,mCCnGA,OACA,OACA,qBCAA,wBAKA,MAJA,OADA,0BAKA,iGCsi1DA"}
\ No newline at end of file
diff --git a/test/debugInfo.fromasm.clamp.no-opts b/test/debugInfo.fromasm.clamp.no-opts
index 9e3050695ed..054226a3a3c 100644
--- a/test/debugInfo.fromasm.clamp.no-opts
+++ b/test/debugInfo.fromasm.clamp.no-opts
@@ -11,15 +11,15 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $x i32) (param $y i32) (result i32)
-  ;; tests/hello_world.c:5
+  ;;@ tests/hello_world.c:5:0
   (set_local $x
    (get_local $x)
   )
-  ;; tests/hello_world.c:6
+  ;;@ tests/hello_world.c:6:0
   (set_local $y
    (get_local $y)
   )
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (set_local $x
    (get_local $y)
   )
@@ -31,14 +31,14 @@
   )
  )
  (func $ret (param $x i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $x
    (i32.shl
     (get_local $x)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (return
    (i32.add
     (get_local $x)
@@ -59,21 +59,21 @@
   )
  )
  (func $opts (param $x i32) (param $y i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $x
    (i32.add
     (get_local $x)
     (get_local $y)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $y
    (i32.shr_s
     (get_local $y)
     (get_local $x)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (set_local $x
    (call $i32s-rem
     (get_local $x)
@@ -102,7 +102,7 @@
   (set_local $sp
    (get_global $STACKTOP)
   )
-  ;; fib.c:3
+  ;;@ fib.c:3:0
   (set_local $$1
    (i32.gt_s
     (get_local $$0)
@@ -126,7 +126,7 @@
     (set_local $$$0$lcssa
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $$$0$lcssa)
     )
@@ -134,21 +134,20 @@
   )
   (loop $while-in
    (block $while-out
-    ;; fib.c:4
+    ;;@ fib.c:4:0
     (set_local $$2
      (i32.add
       (get_local $$$019)
       (get_local $$$01518)
      )
     )
-    ;; fib.c:3
+    ;;@ fib.c:3:0
     (set_local $$3
      (i32.add
       (get_local $$$01617)
       (i32.const 1)
      )
     )
-    ;; fib.c:3
     (set_local $$exitcond
      (i32.eq
       (get_local $$3)
@@ -181,7 +180,7 @@
     (br $while-in)
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (return
    (get_local $$$0$lcssa)
   )
@@ -278,7 +277,7 @@
     (get_local $$p)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (return
    (get_local $$rc$0)
   )
diff --git a/test/debugInfo.fromasm.clamp.no-opts.map b/test/debugInfo.fromasm.clamp.no-opts.map
new file mode 100644
index 00000000000..82a92c68b2e
--- /dev/null
+++ b/test/debugInfo.fromasm.clamp.no-opts.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"uMAIA,IACA,ICyylTA,sBC7vlTA,OAkDA,uCCnGA,OACA,OACA,gCCAA,4BAKA,QAJA,OADA,8CAKA,kJCsi1DA"}
\ No newline at end of file
diff --git a/test/debugInfo.fromasm.imprecise b/test/debugInfo.fromasm.imprecise
index 4919d624dab..638911cfc1c 100644
--- a/test/debugInfo.fromasm.imprecise
+++ b/test/debugInfo.fromasm.imprecise
@@ -10,42 +10,42 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $0 i32) (param $1 i32) (result i32)
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (i32.add
    (get_local $1)
    (get_local $1)
   )
  )
  (func $ret (param $0 i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $0
    (i32.shl
     (get_local $0)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (i32.add
    (get_local $0)
    (i32.const 1)
   )
  )
  (func $opts (param $0 i32) (param $1 i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $0
    (i32.add
     (get_local $0)
     (get_local $1)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $1
    (i32.shr_s
     (get_local $1)
     (get_local $0)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (i32.add
    (i32.rem_s
     (get_local $0)
@@ -60,7 +60,7 @@
   (local $3 i32)
   (local $4 i32)
   (if
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (i32.gt_s
     (get_local $0)
     (i32.const 0)
@@ -80,21 +80,21 @@
     (set_local $1
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $1)
     )
    )
   )
   (loop $while-in
-   ;; fib.c:4
+   ;;@ fib.c:4:0
    (set_local $1
     (i32.add
      (get_local $3)
      (get_local $4)
     )
    )
-   ;; fib.c:3
+   ;;@ fib.c:3:0
    (set_local $2
     (i32.add
      (get_local $2)
@@ -102,7 +102,6 @@
     )
    )
    (if
-    ;; fib.c:3
     (i32.ne
      (get_local $2)
      (get_local $0)
@@ -118,7 +117,7 @@
     )
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (get_local $1)
  )
  (func $switch_reach (param $0 i32) (result i32)
@@ -178,7 +177,7 @@
     (get_local $0)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (get_local $1)
  )
 )
diff --git a/test/debugInfo.fromasm.imprecise.map b/test/debugInfo.fromasm.imprecise.map
new file mode 100644
index 00000000000..60f44708269
--- /dev/null
+++ b/test/debugInfo.fromasm.imprecise.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"wLC8ylTA,cC7vlTA,OAkDA,eCnGA,OACA,OACA,oBCAA,wBAKA,MAJA,OADA,0BAKA,iGCsi1DA"}
\ No newline at end of file
diff --git a/test/debugInfo.fromasm.imprecise.no-opts b/test/debugInfo.fromasm.imprecise.no-opts
index 4bea2c35520..1ec751ef4d0 100644
--- a/test/debugInfo.fromasm.imprecise.no-opts
+++ b/test/debugInfo.fromasm.imprecise.no-opts
@@ -11,15 +11,15 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $x i32) (param $y i32) (result i32)
-  ;; tests/hello_world.c:5
+  ;;@ tests/hello_world.c:5:0
   (set_local $x
    (get_local $x)
   )
-  ;; tests/hello_world.c:6
+  ;;@ tests/hello_world.c:6:0
   (set_local $y
    (get_local $y)
   )
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (set_local $x
    (get_local $y)
   )
@@ -31,14 +31,14 @@
   )
  )
  (func $ret (param $x i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $x
    (i32.shl
     (get_local $x)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (return
    (i32.add
     (get_local $x)
@@ -47,21 +47,21 @@
   )
  )
  (func $opts (param $x i32) (param $y i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $x
    (i32.add
     (get_local $x)
     (get_local $y)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $y
    (i32.shr_s
     (get_local $y)
     (get_local $x)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (set_local $x
    (i32.rem_s
     (get_local $x)
@@ -90,7 +90,7 @@
   (set_local $sp
    (get_global $STACKTOP)
   )
-  ;; fib.c:3
+  ;;@ fib.c:3:0
   (set_local $$1
    (i32.gt_s
     (get_local $$0)
@@ -114,7 +114,7 @@
     (set_local $$$0$lcssa
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $$$0$lcssa)
     )
@@ -122,21 +122,20 @@
   )
   (loop $while-in
    (block $while-out
-    ;; fib.c:4
+    ;;@ fib.c:4:0
     (set_local $$2
      (i32.add
       (get_local $$$019)
       (get_local $$$01518)
      )
     )
-    ;; fib.c:3
+    ;;@ fib.c:3:0
     (set_local $$3
      (i32.add
       (get_local $$$01617)
       (i32.const 1)
      )
     )
-    ;; fib.c:3
     (set_local $$exitcond
      (i32.eq
       (get_local $$3)
@@ -169,7 +168,7 @@
     (br $while-in)
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (return
    (get_local $$$0$lcssa)
   )
@@ -266,7 +265,7 @@
     (get_local $$p)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (return
    (get_local $$rc$0)
   )
diff --git a/test/debugInfo.fromasm.imprecise.no-opts.map b/test/debugInfo.fromasm.imprecise.no-opts.map
new file mode 100644
index 00000000000..2fcda4e2331
--- /dev/null
+++ b/test/debugInfo.fromasm.imprecise.no-opts.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"sMAIA,IACA,ICyylTA,sBC7vlTA,OAkDA,kBCnGA,OACA,OACA,+BCAA,4BAKA,QAJA,OADA,8CAKA,kJCsi1DA"}
\ No newline at end of file
diff --git a/test/debugInfo.fromasm.map b/test/debugInfo.fromasm.map
new file mode 100644
index 00000000000..5680294cda5
--- /dev/null
+++ b/test/debugInfo.fromasm.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"yLC8ylTA,cC7vlTA,OAkDA,mCCnGA,OACA,OACA,qBCAA,wBAKA,MAJA,OADA,0BAKA,iGCsi1DA"}
\ No newline at end of file
diff --git a/test/debugInfo.fromasm.no-opts b/test/debugInfo.fromasm.no-opts
index 9e3050695ed..054226a3a3c 100644
--- a/test/debugInfo.fromasm.no-opts
+++ b/test/debugInfo.fromasm.no-opts
@@ -11,15 +11,15 @@
  (export "fib" (func $fib))
  (export "switch_reach" (func $switch_reach))
  (func $add (param $x i32) (param $y i32) (result i32)
-  ;; tests/hello_world.c:5
+  ;;@ tests/hello_world.c:5:0
   (set_local $x
    (get_local $x)
   )
-  ;; tests/hello_world.c:6
+  ;;@ tests/hello_world.c:6:0
   (set_local $y
    (get_local $y)
   )
-  ;; tests/other_file.cpp:314159
+  ;;@ tests/other_file.cpp:314159:0
   (set_local $x
    (get_local $y)
   )
@@ -31,14 +31,14 @@
   )
  )
  (func $ret (param $x i32) (result i32)
-  ;; return.cpp:50
+  ;;@ return.cpp:50:0
   (set_local $x
    (i32.shl
     (get_local $x)
     (i32.const 1)
    )
   )
-  ;; return.cpp:100
+  ;;@ return.cpp:100:0
   (return
    (i32.add
     (get_local $x)
@@ -59,21 +59,21 @@
   )
  )
  (func $opts (param $x i32) (param $y i32) (result i32)
-  ;; even-opted.cpp:1
+  ;;@ even-opted.cpp:1:0
   (set_local $x
    (i32.add
     (get_local $x)
     (get_local $y)
    )
   )
-  ;; even-opted.cpp:2
+  ;;@ even-opted.cpp:2:0
   (set_local $y
    (i32.shr_s
     (get_local $y)
     (get_local $x)
    )
   )
-  ;; even-opted.cpp:3
+  ;;@ even-opted.cpp:3:0
   (set_local $x
    (call $i32s-rem
     (get_local $x)
@@ -102,7 +102,7 @@
   (set_local $sp
    (get_global $STACKTOP)
   )
-  ;; fib.c:3
+  ;;@ fib.c:3:0
   (set_local $$1
    (i32.gt_s
     (get_local $$0)
@@ -126,7 +126,7 @@
     (set_local $$$0$lcssa
      (i32.const 1)
     )
-    ;; fib.c:8
+    ;;@ fib.c:8:0
     (return
      (get_local $$$0$lcssa)
     )
@@ -134,21 +134,20 @@
   )
   (loop $while-in
    (block $while-out
-    ;; fib.c:4
+    ;;@ fib.c:4:0
     (set_local $$2
      (i32.add
       (get_local $$$019)
       (get_local $$$01518)
      )
     )
-    ;; fib.c:3
+    ;;@ fib.c:3:0
     (set_local $$3
      (i32.add
       (get_local $$$01617)
       (i32.const 1)
      )
     )
-    ;; fib.c:3
     (set_local $$exitcond
      (i32.eq
       (get_local $$3)
@@ -181,7 +180,7 @@
     (br $while-in)
    )
   )
-  ;; fib.c:8
+  ;;@ fib.c:8:0
   (return
    (get_local $$$0$lcssa)
   )
@@ -278,7 +277,7 @@
     (get_local $$p)
    )
   )
-  ;; /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950
+  ;;@ /tmp/emscripten_test_binaryen2_28hnAe/src.c:59950:0
   (return
    (get_local $$rc$0)
   )
diff --git a/test/debugInfo.fromasm.no-opts.map b/test/debugInfo.fromasm.no-opts.map
new file mode 100644
index 00000000000..82a92c68b2e
--- /dev/null
+++ b/test/debugInfo.fromasm.no-opts.map
@@ -0,0 +1 @@
+{"version":3,"sources":["tests/hello_world.c","tests/other_file.cpp","return.cpp","even-opted.cpp","fib.c","/tmp/emscripten_test_binaryen2_28hnAe/src.c"],"names":[],"mappings":"uMAIA,IACA,ICyylTA,sBC7vlTA,OAkDA,uCCnGA,OACA,OACA,gCCAA,4BAKA,QAJA,OADA,8CAKA,kJCsi1DA"}
\ No newline at end of file
diff --git a/test/dot_s/debug.wast b/test/dot_s/debug.wast
index aa4f34d9e71..0cc0ae20c9e 100644
--- a/test/dot_s/debug.wast
+++ b/test/dot_s/debug.wast
@@ -18,18 +18,21 @@
   )
   (block $label$0
    (loop $label$1
+    ;;@ fib.c:3:17
     (set_local $2
      (i32.add
       (get_local $2)
       (i32.const 1)
      )
     )
+    ;;@ fib.c:3:3
     (br_if $label$0
      (i32.ge_s
       (get_local $2)
       (get_local $0)
      )
     )
+    ;;@ fib.c:4:11
     (set_local $1
      (i32.add
       (get_local $4)
@@ -45,6 +48,7 @@
     (br $label$1)
    )
   )
+  ;;@ fib.c:6:3
   (return
    (get_local $4)
   )
diff --git a/test/fib-dbg.wasm b/test/fib-dbg.wasm
new file mode 100644
index 00000000000..8e56773f2c2
Binary files /dev/null and b/test/fib-dbg.wasm differ
diff --git a/test/fib-dbg.wasm.fromBinary b/test/fib-dbg.wasm.fromBinary
new file mode 100644
index 00000000000..3f940fa8ad6
--- /dev/null
+++ b/test/fib-dbg.wasm.fromBinary
@@ -0,0 +1,228 @@
+(module
+ (type $0 (func (param i32 i32)))
+ (type $1 (func (param i32) (result i32)))
+ (type $2 (func (result i32)))
+ (type $3 (func (param i32)))
+ (type $4 (func))
+ (import "env" "DYNAMICTOP_PTR" (global $import$0 i32))
+ (import "env" "tempDoublePtr" (global $import$1 i32))
+ (import "env" "ABORT" (global $import$2 i32))
+ (import "env" "STACKTOP" (global $import$3 i32))
+ (import "env" "STACK_MAX" (global $import$4 i32))
+ (import "env" "gb" (global $import$5 i32))
+ (import "env" "fb" (global $import$6 i32))
+ (import "global" "NaN" (global $import$7 f64))
+ (import "global" "Infinity" (global $import$8 f64))
+ (import "env" "memory" (memory $0 256 256))
+ (import "env" "table" (table 0 0 anyfunc))
+ (import "env" "memoryBase" (global $import$11 i32))
+ (import "env" "tableBase" (global $import$12 i32))
+ (global $global$0 (mut i32) (get_global $import$0))
+ (global $global$1 (mut i32) (get_global $import$1))
+ (global $global$2 (mut i32) (get_global $import$2))
+ (global $global$3 (mut i32) (get_global $import$3))
+ (global $global$4 (mut i32) (get_global $import$4))
+ (global $global$5 (mut i32) (get_global $import$5))
+ (global $global$6 (mut i32) (get_global $import$6))
+ (global $global$7 (mut i32) (i32.const 0))
+ (global $global$8 (mut i32) (i32.const 0))
+ (global $global$9 (mut i32) (i32.const 0))
+ (global $global$10 (mut i32) (i32.const 0))
+ (global $global$11 (mut f64) (get_global $import$7))
+ (global $global$12 (mut f64) (get_global $import$8))
+ (global $global$13 (mut i32) (i32.const 0))
+ (global $global$14 (mut i32) (i32.const 0))
+ (global $global$15 (mut i32) (i32.const 0))
+ (global $global$16 (mut i32) (i32.const 0))
+ (global $global$17 (mut f64) (f64.const 0))
+ (global $global$18 (mut i32) (i32.const 0))
+ (global $global$19 (mut i32) (i32.const 0))
+ (global $global$20 (mut i32) (i32.const 0))
+ (global $global$21 (mut f64) (f64.const 0))
+ (global $global$22 (mut i32) (i32.const 0))
+ (global $global$23 (mut f64) (f64.const 0))
+ (export "setThrew" (func $setThrew))
+ (export "runPostSets" (func $runPostSets))
+ (export "establishStackSpace" (func $establishStackSpace))
+ (export "stackSave" (func $stackSave))
+ (export "stackRestore" (func $stackRestore))
+ (export "_fib" (func $_fib))
+ (export "stackAlloc" (func $stackAlloc))
+ (func $stackAlloc (type $1) (param $var$0 i32) (result i32)
+  (local $var$1 i32)
+  (block $label$0
+   (set_local $var$1
+    (get_global $global$3)
+   )
+   (set_global $global$3
+    (i32.add
+     (get_global $global$3)
+     (get_local $var$0)
+    )
+   )
+   (set_global $global$3
+    (i32.and
+     (i32.add
+      (get_global $global$3)
+      (i32.const 15)
+     )
+     (i32.const -16)
+    )
+   )
+   (return
+    (get_local $var$1)
+   )
+   (unreachable)
+  )
+  (unreachable)
+ )
+ (func $stackSave (type $2) (result i32)
+  (return
+   (get_global $global$3)
+  )
+ )
+ (func $stackRestore (type $3) (param $var$0 i32)
+  (set_global $global$3
+   (get_local $var$0)
+  )
+ )
+ (func $establishStackSpace (type $0) (param $var$0 i32) (param $var$1 i32)
+  (block $label$0
+   (set_global $global$3
+    (get_local $var$0)
+   )
+   (set_global $global$4
+    (get_local $var$1)
+   )
+  )
+ )
+ (func $setThrew (type $0) (param $var$0 i32) (param $var$1 i32)
+  (if
+   (i32.eq
+    (get_global $global$7)
+    (i32.const 0)
+   )
+   (block $label$0
+    (set_global $global$7
+     (get_local $var$0)
+    )
+    (set_global $global$8
+     (get_local $var$1)
+    )
+   )
+  )
+ )
+ (func $_fib (type $1) (param $var$0 i32) (result i32)
+  (local $var$1 i32)
+  (local $var$2 i32)
+  (local $var$3 i32)
+  (local $var$4 i32)
+  (local $var$5 i32)
+  (local $var$6 i32)
+  (local $var$7 i32)
+  (local $var$8 i32)
+  (local $var$9 i32)
+  (local $var$10 i32)
+  (local $var$11 i32)
+  ;;@ fib.c:8:0
+  (block $label$0
+   (set_local $var$11
+    (get_global $global$3)
+   )
+   ;;@ fib.c:3:0
+   (set_local $var$6
+    (i32.gt_s
+     (get_local $var$0)
+     (i32.const 0)
+    )
+   )
+   ;;@ fib.c:8:0
+   (if
+    ;;@ fib.c:3:0
+    (get_local $var$6)
+    (block $label$1
+     (set_local $var$1
+      (i32.const 0)
+     )
+     (set_local $var$5
+      (i32.const 1)
+     )
+     (set_local $var$8
+      (i32.const 0)
+     )
+    )
+    (block $label$2
+     (set_local $var$4
+      (i32.const 1)
+     )
+     ;;@ fib.c:8:0
+     (return
+      (get_local $var$4)
+     )
+    )
+   )
+   ;;@ fib.c:3:0
+   (loop $label$3
+    (block $label$4
+     ;;@ fib.c:4:0
+     (set_local $var$3
+      (i32.add
+       (get_local $var$5)
+       (get_local $var$1)
+      )
+     )
+     ;;@ fib.c:3:0
+     (set_local $var$9
+      (i32.add
+       (get_local $var$8)
+       (i32.const 1)
+      )
+     )
+     (set_local $var$7
+      (i32.eq
+       (get_local $var$9)
+       (get_local $var$0)
+      )
+     )
+     (if
+      (get_local $var$7)
+      (block $label$5
+       (set_local $var$4
+        (get_local $var$3)
+       )
+       (br $label$4)
+      )
+      (block $label$6
+       (set_local $var$2
+        (get_local $var$5)
+       )
+       (set_local $var$5
+        (get_local $var$3)
+       )
+       (set_local $var$8
+        (get_local $var$9)
+       )
+       (set_local $var$1
+        (get_local $var$2)
+       )
+      )
+     )
+     (br $label$3)
+    )
+   )
+   ;;@ fib.c:8:0
+   (return
+    (get_local $var$4)
+   )
+   (unreachable)
+   (unreachable)
+  )
+  (unreachable)
+ )
+ (func $runPostSets (type $4)
+  (local $var$0 i32)
+  (nop)
+ )
+ ;; custom section "sourceMappingURL", size 35
+)
+
diff --git a/test/fib-dbg.wasm.map b/test/fib-dbg.wasm.map
new file mode 100644
index 00000000000..831f55fbd27
--- /dev/null
+++ b/test/fib-dbg.wasm.map
@@ -0,0 +1 @@
+{"version":3,"sources":["fib.c"],"names":[],"mappings":"moBAEA,4BAKA,QAJA,OADA,OAAA,uCAKA"}