diff --git a/auto_update_tests.py b/auto_update_tests.py
index 7a14f6521aa..98c1c246c31 100755
--- a/auto_update_tests.py
+++ b/auto_update_tests.py
@@ -21,6 +21,8 @@
             cmd += ['-O0'] # test that -O0 does nothing
         else:
           cmd += ['-O']
+        if 'debugInfo' in asm:
+          cmd += ['-g']
         if precise and opts:
           # test mem init importing
           open('a.mem', 'wb').write(asm)
diff --git a/check.py b/check.py
index 7be44e63b54..e31ad0f0a2c 100755
--- a/check.py
+++ b/check.py
@@ -107,6 +107,8 @@
             cmd += ['-O0'] # test that -O0 does nothing
         else:
           cmd += ['-O']
+        if 'debugInfo' in asm:
+          cmd += ['-g']
         if precise and opts:
           # test mem init importing
           open('a.mem', 'wb').write(asm)
diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index d23e811ca20..712019d7a65 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -34,6 +34,7 @@
 #include "ast_utils.h"
 #include "wasm-builder.h"
 #include "wasm-emscripten.h"
+#include "wasm-printing.h"
 #include "wasm-validator.h"
 #include "wasm-module-building.h"
 
@@ -109,7 +110,8 @@ Name I32_CTTZ("i32_cttz"),
      FTCALL("ftCall_"),
      MFTCALL("mftCall_"),
      MAX_("max"),
-     MIN_("min");
+     MIN_("min"),
+     EMSCRIPTEN_DEBUGINFO("emscripten_debuginfo");
 
 // Utilities
 
@@ -160,6 +162,12 @@ struct Asm2WasmPreProcessor {
   std::vector<std::string> debugInfoFileNames;
   std::unordered_map<std::string, Index> debugInfoFileIndices;
 
+  char* allocatedCopy = nullptr;
+
+  ~Asm2WasmPreProcessor() {
+    if (allocatedCopy) free(allocatedCopy);
+  }
+
   char* process(char* input) {
     // emcc --separate-asm modules can look like
     //
@@ -222,10 +230,10 @@ struct Asm2WasmPreProcessor {
       // and is usually decently accurate with them.
       auto size = strlen(input);
       auto upperBound = Index(size * 1.25) + 100;
-      char* copy = (char*)malloc(upperBound);
+      char* copy = allocatedCopy = (char*)malloc(upperBound);
       char* end = copy + upperBound;
       char* out = copy;
-      std::string DEBUGINFO_INTRINSIC = "emscripten_debuginfo";
+      std::string DEBUGINFO_INTRINSIC = EMSCRIPTEN_DEBUGINFO.str;
       auto DEBUGINFO_INTRINSIC_SIZE = DEBUGINFO_INTRINSIC.size();
       bool seenUseAsm = false;
       while (input[0]) {
@@ -313,7 +321,7 @@ class Asm2WasmBuilder {
   // function table
   std::map<IString, int> functionTableStarts; // each asm function table gets a range in the one wasm table, starting at a location
 
-  bool memoryGrowth;
+  Asm2WasmPreProcessor& preprocessor;
   bool debug;
   bool imprecise;
   PassOptions passOptions;
@@ -419,11 +427,11 @@ class Asm2WasmBuilder {
   }
 
 public:
- Asm2WasmBuilder(Module& wasm, bool memoryGrowth, bool debug, bool imprecise, PassOptions passOptions, bool runOptimizationPasses, bool wasmOnly)
+ Asm2WasmBuilder(Module& wasm, Asm2WasmPreProcessor& preprocessor, bool debug, bool imprecise, PassOptions passOptions, bool runOptimizationPasses, bool wasmOnly)
      : wasm(wasm),
        allocator(wasm.allocator),
        builder(wasm),
-       memoryGrowth(memoryGrowth),
+       preprocessor(preprocessor),
        debug(debug),
        imprecise(imprecise),
        passOptions(passOptions),
@@ -641,6 +649,16 @@ class Asm2WasmBuilder {
   }
 
   Function* processFunction(Ref ast);
+
+public:
+  CallImport* isDebugInfo(Expression* curr) {
+    if (auto* call = curr->dynCast<CallImport>()) {
+      if (call->target == EMSCRIPTEN_DEBUGINFO) {
+        return call;
+      }
+    }
+    return nullptr;
+  }
 };
 
 void Asm2WasmBuilder::processAsm(Ref ast) {
@@ -1090,6 +1108,43 @@ void Asm2WasmBuilder::processAsm(Ref ast) {
     }
   };
 
+  // apply debug info, reducing intrinsic calls into annotations on the ast nodes
+  struct ApplyDebugInfo : public WalkerPass<PostWalker<ApplyDebugInfo, UnifiedExpressionVisitor<ApplyDebugInfo>>> {
+    bool isFunctionParallel() override { return true; }
+
+    Pass* create() override { return new ApplyDebugInfo(parent); }
+
+    Asm2WasmBuilder* parent;
+
+    ApplyDebugInfo(Asm2WasmBuilder* parent) : parent(parent) {
+      name = "apply-debug-info";
+    }
+
+    Expression* lastExpression = nullptr;
+
+    void visitExpression(Expression* curr) {
+      if (auto* call = parent->isDebugInfo(curr)) {
+        // this is a debuginfo node. turn it into an annotation on the last stack
+        auto* last = lastExpression;
+        lastExpression = nullptr;
+        auto& annotations = getFunction()->annotations;
+        if (last) {
+          auto fileIndex = call->operands[0]->cast<Const>()->value.geti32();
+          auto lineNumber = call->operands[1]->cast<Const>()->value.geti32();
+          annotations[last] = parent->preprocessor.debugInfoFileNames[fileIndex] + ":" + std::to_string(lineNumber);
+        }
+        // eliminate the debug info call
+        ExpressionManipulator::nop(curr);
+        return;
+      }
+      // ignore const nodes, as they may be the children of the debug info calls, and they
+      // don't really need debug info anyhow
+      if (!curr->is<Const>()) {
+        lastExpression = curr;
+      }
+    }
+  };
+
   PassRunner passRunner(&wasm);
   if (debug) {
     passRunner.setDebug(true);
@@ -1106,13 +1161,17 @@ void Asm2WasmBuilder::processAsm(Ref ast) {
     passRunner.add("optimize-instructions");
     passRunner.add("post-emscripten");
   }
+  if (preprocessor.debugInfo) {
+    passRunner.add<ApplyDebugInfo>(this);
+    passRunner.add("vacuum"); // FIXME maybe just remove the nops that were debuginfo nodes, if not optimizing?
+  }
   // make sure to not emit unreachable code at all, even in -O0, as wasm rules for it are complex
   // and changing.
   passRunner.add("dce");
   passRunner.run();
 
   // apply memory growth, if relevant
-  if (memoryGrowth) {
+  if (preprocessor.memoryGrowth) {
     emscripten::generateMemoryGrowthFunction(wasm);
     wasm.memory.max = Memory::kMaxSize;
   }
@@ -2349,6 +2408,27 @@ Function* Asm2WasmBuilder::processFunction(Ref ast) {
   };
   // body
   function->body = processStatements(body, start);
+  // debug info cleanup: we add debug info calls after each instruction; as
+  // a result,
+  //   return 0; //@line file.cpp
+  // will have code after the return. if the function body is a block,
+  // it will be forced to the return type of the function, and then
+  // the unreachable type of the return makes things work, which we break
+  // if we add a none debug intrinsic call afterwards. so we need to fix
+  // that up.
+  if (preprocessor.debugInfo) {
+    if (function->result != none) {
+      if (auto* block = function->body->dynCast<Block>()) {
+        if (block->list.size() > 0) {
+          if (isDebugInfo(block->list.back())) {
+            // add an unreachable. both the debug info and it could be dce'd,
+            // but it makes us validate properly.
+            block->list.push_back(builder.makeUnreachable());
+          }
+        }
+      }
+    }
+  }
   // cleanups/checks
   assert(breakStack.size() == 0 && continueStack.size() == 0);
   assert(parentLabel.isNull());
diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 3c847809ff7..e5ff03fae9f 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -45,6 +45,19 @@ struct PrintSExpression : public Visitor<PrintSExpression> {
     }
   }
 
+  void visit(Expression* curr) {
+    if (currFunction) {
+      // show an annotation, if there is one
+      auto& annotations = currFunction->annotations;
+      auto iter = annotations.find(curr);
+      if (iter != annotations.end()) {
+        o << ";; " << iter->second << '\n';
+        doIndent(o, indent);
+      }
+    }
+    Visitor<PrintSExpression>::visit(curr);
+  }
+
   void setMinify(bool minify_) {
     minify = minify_;
     maybeSpace = minify ? "" : " ";
diff --git a/src/tools/asm2wasm.cpp b/src/tools/asm2wasm.cpp
index 3517a3ec5cf..e23b3f39342 100644
--- a/src/tools/asm2wasm.cpp
+++ b/src/tools/asm2wasm.cpp
@@ -84,7 +84,7 @@ int main(int argc, const char *argv[]) {
            [&wasmOnly](Options *o, const std::string &) {
              wasmOnly = true;
            })
-      .add("--debuginfo", "-g", "Emit names section and debug info",
+      .add("--debuginfo", "-g", "Emit names section and debug info (you must emit text, -S, for this to work)",
            Options::Arguments::Zero,
            [&](Options *o, const std::string &arguments) { debugInfo = true; })
       .add("--symbolmap", "-s", "Emit a symbol map (indexes => names)",
@@ -99,6 +99,16 @@ int main(int argc, const char *argv[]) {
                       });
   options.parse(argc, argv);
 
+  // finalize arguments
+  if (options.extra["output"].size() == 0) {
+    // when no output file is specified, we emit text to stdout
+    emitBinary = false;
+  }
+  if (emitBinary) {
+    // wasm binaries can't contain debug info yet
+    debugInfo = false;
+  }
+
   const auto &tm_it = options.extra.find("total memory");
   size_t totalMemory =
       tm_it == options.extra.end() ? 16 * 1024 * 1024 : atoi(tm_it->second.c_str());
@@ -121,7 +131,7 @@ int main(int argc, const char *argv[]) {
   if (options.debug) std::cerr << "wasming..." << std::endl;
   Module wasm;
   wasm.memory.initial = wasm.memory.max = totalMemory / Memory::kPageSize;
-  Asm2WasmBuilder asm2wasm(wasm, pre.memoryGrowth, options.debug, imprecise, passOptions, runOptimizationPasses, wasmOnly);
+  Asm2WasmBuilder asm2wasm(wasm, pre, options.debug, imprecise, passOptions, runOptimizationPasses, wasmOnly);
   asm2wasm.processAsm(asmjs);
 
   // import mem init file, if provided
diff --git a/src/wasm.h b/src/wasm.h
index 75d6a174c52..31dafb84bcc 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -1385,6 +1385,9 @@ class Function {
   std::vector<Name> localNames;
   std::map<Name, Index> localIndices;
 
+  // node annotations, printed alongside the node in the text format
+  std::unordered_map<Expression*, std::string> annotations;
+
   Function() : result(none) {}
 
   size_t getNumParams() {
diff --git a/test/debugInfo.asm.js b/test/debugInfo.asm.js
new file mode 100644
index 00000000000..929d7980452
--- /dev/null
+++ b/test/debugInfo.asm.js
@@ -0,0 +1,26 @@
+function () {
+  "use asm";
+  function add(x, y) {
+    x = x | 0;
+    y = y | 0;
+    x = x; //@line 5 "tests/hello_world.c"
+    y = y; //@line 6 "tests/hello_world.c"
+    x = y; //@line 314159 "tests/other_file.cpp"
+    return x + y | 0;
+  }
+  function ret(x) {
+    x = x | 0;
+    x = x << 1; //@line 50 "return.cpp"
+    return x + 1 | 0; //@line 100 "return.cpp"
+  }
+  function opts(x, y) {
+    x = x | 0;
+    y = y | 0;
+    x = (x + y) | 0; //@line 1 "even-opted.cpp"
+    y = y >> x; //@line 2 "even-opted.cpp"
+    x = (x | 0) % (y | 0); //@line 3 "even-opted.cpp"
+    return x + y | 0;
+  }
+  return { add: add, ret: ret, opts: opts };
+}
+
diff --git a/test/debugInfo.fromasm b/test/debugInfo.fromasm
new file mode 100644
index 00000000000..07ae6fb44ff
--- /dev/null
+++ b/test/debugInfo.fromasm
@@ -0,0 +1,54 @@
+(module
+  (type $FUNCSIG$iii (func (param i32 i32) (result i32)))
+  (type $FUNCSIG$vii (func (param i32 i32)))
+  (import "env" "emscripten_debuginfo" (func $emscripten_debuginfo (param i32 i32)))
+  (import "asm2wasm" "i32s-rem" (func $i32s-rem (param i32 i32) (result i32)))
+  (import "env" "memory" (memory $0 256 256))
+  (import "env" "table" (table 0 0 anyfunc))
+  (import "env" "memoryBase" (global $memoryBase i32))
+  (import "env" "tableBase" (global $tableBase i32))
+  (data (get_global $memoryBase) "debugInfo.asm.js")
+  (export "add" (func $add))
+  (export "ret" (func $ret))
+  (export "opts" (func $opts))
+  (func $add (param $0 i32) (param $1 i32) (result i32)
+    (i32.add
+      (get_local $1)
+      (get_local $1)
+    )
+  )
+  (func $ret (param $0 i32) (result i32)
+    (i32.add
+      (i32.shl
+        (get_local $0)
+        (i32.const 1)
+      )
+      (i32.const 1)
+    )
+  )
+  (func $opts (param $0 i32) (param $1 i32) (result i32)
+    ;; even-opted.cpp:2
+    (set_local $1
+      (i32.shr_s
+        (get_local $1)
+        (tee_local $0
+          (i32.add
+            (get_local $0)
+            (get_local $1)
+          )
+        )
+      )
+    )
+    ;; even-opted.cpp:3
+    (set_local $0
+      (call $i32s-rem
+        (get_local $0)
+        (get_local $1)
+      )
+    )
+    (i32.add
+      (get_local $0)
+      (get_local $1)
+    )
+  )
+)
diff --git a/test/debugInfo.fromasm.imprecise b/test/debugInfo.fromasm.imprecise
new file mode 100644
index 00000000000..ad881983cc1
--- /dev/null
+++ b/test/debugInfo.fromasm.imprecise
@@ -0,0 +1,47 @@
+(module
+  (type $FUNCSIG$vii (func (param i32 i32)))
+  (import "env" "emscripten_debuginfo" (func $emscripten_debuginfo (param i32 i32)))
+  (import "env" "memory" (memory $0 256 256))
+  (import "env" "table" (table 0 0 anyfunc))
+  (import "env" "memoryBase" (global $memoryBase i32))
+  (import "env" "tableBase" (global $tableBase i32))
+  (export "add" (func $add))
+  (export "ret" (func $ret))
+  (export "opts" (func $opts))
+  (func $add (param $0 i32) (param $1 i32) (result i32)
+    (i32.add
+      (get_local $1)
+      (get_local $1)
+    )
+  )
+  (func $ret (param $0 i32) (result i32)
+    (i32.add
+      (i32.shl
+        (get_local $0)
+        (i32.const 1)
+      )
+      (i32.const 1)
+    )
+  )
+  (func $opts (param $0 i32) (param $1 i32) (result i32)
+    ;; even-opted.cpp:2
+    (set_local $1
+      (i32.shr_s
+        (get_local $1)
+        (tee_local $0
+          (i32.add
+            (get_local $0)
+            (get_local $1)
+          )
+        )
+      )
+    )
+    (i32.add
+      (i32.rem_s
+        (get_local $0)
+        (get_local $1)
+      )
+      (get_local $1)
+    )
+  )
+)
diff --git a/test/debugInfo.fromasm.imprecise.no-opts b/test/debugInfo.fromasm.imprecise.no-opts
new file mode 100644
index 00000000000..8433e161c26
--- /dev/null
+++ b/test/debugInfo.fromasm.imprecise.no-opts
@@ -0,0 +1,76 @@
+(module
+  (type $FUNCSIG$vii (func (param i32 i32)))
+  (import "env" "emscripten_debuginfo" (func $emscripten_debuginfo (param i32 i32)))
+  (import "env" "memory" (memory $0 256 256))
+  (import "env" "table" (table 0 0 anyfunc))
+  (import "env" "memoryBase" (global $memoryBase i32))
+  (import "env" "tableBase" (global $tableBase i32))
+  (export "add" (func $add))
+  (export "ret" (func $ret))
+  (export "opts" (func $opts))
+  (func $add (param $x i32) (param $y i32) (result i32)
+    ;; tests/hello_world.c:5
+    (set_local $x
+      (get_local $x)
+    )
+    ;; tests/hello_world.c:6
+    (set_local $y
+      (get_local $y)
+    )
+    ;; tests/other_file.cpp:314159
+    (set_local $x
+      (get_local $y)
+    )
+    (return
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+  )
+  (func $ret (param $x i32) (result i32)
+    ;; return.cpp:50
+    (set_local $x
+      (i32.shl
+        (get_local $x)
+        (i32.const 1)
+      )
+    )
+    ;; return.cpp:100
+    (return
+      (i32.add
+        (get_local $x)
+        (i32.const 1)
+      )
+    )
+  )
+  (func $opts (param $x i32) (param $y i32) (result i32)
+    ;; even-opted.cpp:1
+    (set_local $x
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+    ;; even-opted.cpp:2
+    (set_local $y
+      (i32.shr_s
+        (get_local $y)
+        (get_local $x)
+      )
+    )
+    ;; even-opted.cpp:3
+    (set_local $x
+      (i32.rem_s
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+    (return
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+  )
+)
diff --git a/test/debugInfo.fromasm.no-opts b/test/debugInfo.fromasm.no-opts
new file mode 100644
index 00000000000..78b1a2b071c
--- /dev/null
+++ b/test/debugInfo.fromasm.no-opts
@@ -0,0 +1,78 @@
+(module
+  (type $FUNCSIG$iii (func (param i32 i32) (result i32)))
+  (type $FUNCSIG$vii (func (param i32 i32)))
+  (import "env" "emscripten_debuginfo" (func $emscripten_debuginfo (param i32 i32)))
+  (import "asm2wasm" "i32s-rem" (func $i32s-rem (param i32 i32) (result i32)))
+  (import "env" "memory" (memory $0 256 256))
+  (import "env" "table" (table 0 0 anyfunc))
+  (import "env" "memoryBase" (global $memoryBase i32))
+  (import "env" "tableBase" (global $tableBase i32))
+  (export "add" (func $add))
+  (export "ret" (func $ret))
+  (export "opts" (func $opts))
+  (func $add (param $x i32) (param $y i32) (result i32)
+    ;; tests/hello_world.c:5
+    (set_local $x
+      (get_local $x)
+    )
+    ;; tests/hello_world.c:6
+    (set_local $y
+      (get_local $y)
+    )
+    ;; tests/other_file.cpp:314159
+    (set_local $x
+      (get_local $y)
+    )
+    (return
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+  )
+  (func $ret (param $x i32) (result i32)
+    ;; return.cpp:50
+    (set_local $x
+      (i32.shl
+        (get_local $x)
+        (i32.const 1)
+      )
+    )
+    ;; return.cpp:100
+    (return
+      (i32.add
+        (get_local $x)
+        (i32.const 1)
+      )
+    )
+  )
+  (func $opts (param $x i32) (param $y i32) (result i32)
+    ;; even-opted.cpp:1
+    (set_local $x
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+    ;; even-opted.cpp:2
+    (set_local $y
+      (i32.shr_s
+        (get_local $y)
+        (get_local $x)
+      )
+    )
+    ;; even-opted.cpp:3
+    (set_local $x
+      (call $i32s-rem
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+    (return
+      (i32.add
+        (get_local $x)
+        (get_local $y)
+      )
+    )
+  )
+)
diff --git a/test/passes/dce.txt b/test/passes/dce.txt
index 71b46bd9409..84757294ac2 100644
--- a/test/passes/dce.txt
+++ b/test/passes/dce.txt
@@ -332,4 +332,9 @@
   (func $global (type $1)
     (unreachable)
   )
+  (func $ret (type $2) (result i32)
+    (return
+      (i32.const 0)
+    )
+  )
 )
diff --git a/test/passes/dce.wast b/test/passes/dce.wast
index ad1d1d3c0d7..b7d903e6bf4 100644
--- a/test/passes/dce.wast
+++ b/test/passes/dce.wast
@@ -435,4 +435,10 @@
     (drop (get_global $x))
     (set_global $x (i32.const 1))
   )
+  (func $ret (result i32)
+    (return
+      (i32.const 0)
+    )
+    (nop)
+  )
 )