Remove wasm offset converter (#24963)

The v8 bug that made this necessary was fixed in 2019:
https://crbug.com/v8/9172

From running some tests I confirmed the node v12 and newer work fine
without the offset converter. Older node versions such as v10 will show
a warning about the legacy backtrace format and will not see symbol
names in their backtraces (when using ASAN etc).

Fixes: #24587

Author: sbc100

ChangeLog.md

@@ -20,6 +20,9 @@ See docs/process.md for more on how version tagging works.
 
 4.0.14 (in development)
 -----------------------
+- The wasm offset converter was removed along with the `WASM_OFFSET_CONVERTER`
+  setting. This feature only existed to work around an old v8 bug that was fixed
+  back in 2019. (#24963)
 
 4.0.13 - 08/14/25
 -----------------

eslint.config.mjs

@@ -43,7 +43,6 @@ export default [{
     'src/webGLClient.js',
     'src/webGLWorker.js',
     'src/*_shell_read.js',
-    'src/wasm_offset_converter.js',
     'src/threadprofiler.js',
     'src/cpuprofiler.js',
     'src/memoryprofiler.js',

site/source/docs/tools_reference/settings_reference.rst

@@ -3053,18 +3053,6 @@ future release.
 
 Default value: -1
 
-.. _use_offset_converter:
-
-USE_OFFSET_CONVERTER
-====================
-
-Whether we should use the offset converter.  This is needed for older
-versions of v8 (<7.7) that does not give the hex module offset into wasm
-binary in stack traces, as well as for avoiding using source map entries
-across function boundaries.
-
-Default value: false
-
 .. _load_source_map:
 
 LOAD_SOURCE_MAP

src/lib/libpthread.js

@@ -355,9 +355,6 @@ var LibraryPThread = {
 #if LOAD_SOURCE_MAP
         wasmSourceMap,
 #endif
-#if USE_OFFSET_CONVERTER
-        wasmOffsetConverter,
-#endif
 #if MAIN_MODULE
         dynamicLibraries,
         // Share all modules that have been loaded so far.  New workers

src/lib/libstack_trace.js

@@ -104,19 +104,14 @@ var LibraryStackTrace = {
     var match;
 
     if (match = /\bwasm-function\[\d+\]:(0x[0-9a-f]+)/.exec(frame)) {
-      // some engines give the binary offset directly, so we use that as return address
+      // Wasm engines give the binary offset directly, so we use that as return address
       return +match[1];
-    } else if (match = /\bwasm-function\[(\d+)\]:(\d+)/.exec(frame)) {
-      // Older versions of v8 give function index and offset in the function,
-      // so we try using the offset converter. If that doesn't work,
-      // we pack index and offset into a "return address"
-#if !USE_OFFSET_CONVERTER
-      abort('Legacy backtrace format detected but -sUSE_OFFSET_CONVERTER not present.')
-#else
 #if ASSERTIONS
-      assert(wasmOffsetConverter, 'wasmOffsetConverter global not found');
-#endif
-      return wasmOffsetConverter.convert(+match[1], +match[2]);
+    } else if (match = /\bwasm-function\[(\d+)\]:(\d+)/.exec(frame)) {
+      // Older versions of v8 (e.g node v10) give function index and offset in
+      // the function.  That format is not supported since it does not provide
+      // the information we need to map the frame to a global program counter.
+      warnOnce('legacy backtrace format detected, this version of v8 is no longer supported by the emscripten backtrace mechanism')
 #endif
     } else if (match = /:(\d+):\d+(?:\)|$)/.exec(frame)) {
       // If we are in js, we can use the js line number as the "return address".
@@ -205,12 +200,12 @@ var LibraryStackTrace = {
   $saveInUnwindCache__deps: ['$UNWIND_CACHE', '$convertFrameToPC'],
   $saveInUnwindCache__internal: true,
   $saveInUnwindCache: (callstack) => {
-    callstack.forEach((frame) => {
-      var pc = convertFrameToPC(frame);
+    for (var line of callstack) {
+      var pc = convertFrameToPC(line);
       if (pc) {
-        UNWIND_CACHE[pc] = frame;
+        UNWIND_CACHE[pc] = line;
       }
-    });
+    }
   },
 
   // Unwinds the stack from a cached PC value. See emscripten_stack_snapshot for
@@ -242,32 +237,37 @@ var LibraryStackTrace = {
   },
 
   // Look up the function name from our stack frame cache with our PC representation.
-  emscripten_pc_get_function__deps: ['$UNWIND_CACHE', 'free', '$stringToNewUTF8'],
+  emscripten_pc_get_function__deps: ['$UNWIND_CACHE', 'free', '$stringToNewUTF8', 'emscripten_stack_snapshot'],
   // Don't treat allocation of _emscripten_pc_get_function.ret as a leak
   emscripten_pc_get_function__noleakcheck: true,
   emscripten_pc_get_function: (pc) => {
-    var name;
-    if (pc & 0x80000000) {
-      // If this is a JavaScript function, try looking it up in the unwind cache.
-      var frame = UNWIND_CACHE[pc];
-      if (!frame) return 0;
+    var frame = UNWIND_CACHE[pc];
+    if (!frame) return 0;
+    dbg(getCallstack())
 
-      var match;
-      if (match = /^\s+at (.*) \(.*\)$/.exec(frame)) {
-        name = match[1];
-      } else if (match = /^(.+?)@/.exec(frame)) {
-        name = match[1];
-      } else {
-        return 0;
-      }
+    var name;
+    var match;
+    // First try to match foo.wasm.sym files explcitly. e.g.
+    //
+    //   at test_return_address.wasm.main (wasm://wasm/test_return_address.wasm-0012cc2a:wasm-function[26]:0x9f3
+    //
+    // Then match JS symbols which don't include that module name:
+    //
+    //   at invokeEntryPoint (.../test_return_address.js:1500:42)
+    //
+    // Finally match firefox format:
+    //
+    //   Object._main@http://server.com:4324:12'
+    if (match = /^\s+at .*\.wasm\.(.*) \(.*\)$/.exec(frame)) {
+      name = match[1];
+    } else if (match = /^\s+at (.*) \(.*\)$/.exec(frame)) {
+      name = match[1];
+    } else if (match = /^(.+?)@/.exec(frame)) {
+      name = match[1];
     } else {
-#if !USE_OFFSET_CONVERTER
-      abort('Cannot use emscripten_pc_get_function on native functions without -sUSE_OFFSET_CONVERTER');
       return 0;
-#else
-      name = wasmOffsetConverter.getName(pc);
-#endif
     }
+
     _free(_emscripten_pc_get_function.ret ?? 0);
     _emscripten_pc_get_function.ret = stringToNewUTF8(name);
     return _emscripten_pc_get_function.ret;

src/modules.mjs

@@ -452,10 +452,6 @@ function exportRuntimeSymbols() {
     runtimeElements.push('HEAP_DATA_VIEW');
   }
 
-  if (USE_OFFSET_CONVERTER) {
-    runtimeElements.push('WasmOffsetConverter');
-  }
-
   if (LOAD_SOURCE_MAP) {
     runtimeElements.push('WasmSourceMap');
   }

src/postamble_minimal.js

@@ -190,13 +190,6 @@ WebAssembly.instantiate(Module['wasm'], imports).then(/** @suppress {missingProp
   wasmExports = applySignatureConversions(wasmExports);
 #endif
 
-#if USE_OFFSET_CONVERTER
-#if PTHREADS
-  if (!ENVIRONMENT_IS_PTHREAD)
-#endif
-    wasmOffsetConverter = new WasmOffsetConverter(Module['wasm'], output.module);
-#endif
-
 #if !DECLARE_ASM_MODULE_EXPORTS
   exportWasmSymbols(wasmExports);
 #else

src/preamble.js

@@ -417,7 +417,7 @@ function receiveSourceMapJSON(sourceMap) {
 }
 #endif
 
-#if (PTHREADS || WASM_WORKERS) && (LOAD_SOURCE_MAP || USE_OFFSET_CONVERTER)
+#if (PTHREADS || WASM_WORKERS) && LOAD_SOURCE_MAP
 // When using postMessage to send an object, it is processed by the structured
 // clone algorithm.  The prototype, and hence methods, on that object is then
 // lost. This function adds back the lost prototype.  This does not work with
@@ -557,9 +557,6 @@ function instantiateSync(file, info) {
   module = new WebAssembly.Module(binary);
 #endif // NODE_CODE_CACHING
   var instance = new WebAssembly.Instance(module, info);
-#if USE_OFFSET_CONVERTER
-  wasmOffsetConverter = new WasmOffsetConverter(binary, module);
-#endif
 #if LOAD_SOURCE_MAP
   receiveSourceMapJSON(getSourceMap());
 #endif
@@ -572,11 +569,6 @@ async function instantiateArrayBuffer(binaryFile, imports) {
   try {
     var binary = await getWasmBinary(binaryFile);
     var instance = await WebAssembly.instantiate(binary, imports);
-#if USE_OFFSET_CONVERTER
-    // wasmOffsetConverter needs to be assigned before calling resolve.
-    // See comments below in instantiateAsync.
-    wasmOffsetConverter = new WasmOffsetConverter(binary, instance.module);
-#endif
     return instance;
   } catch (reason) {
     err(`failed to asynchronously prepare wasm: ${reason}`);
@@ -635,31 +627,7 @@ async function instantiateAsync(binary, binaryFile, imports) {
      ) {
     try {
       var response = fetch(binaryFile, {{{ makeModuleReceiveExpr('fetchSettings', "{ credentials: 'same-origin' }") }}});
-#if USE_OFFSET_CONVERTER
-      // We need the wasm binary for the offset converter. Clone the response
-      // in order to get its arrayBuffer (cloning should be more efficient
-      // than doing another entire request).
-      // (We must clone the response now in order to use it later, as if we
-      // try to clone it asynchronously lower down then we will get a
-      // "response was already consumed" error.)
-      var clonedResponse = (await response).clone();
-#endif
       var instantiationResult = await WebAssembly.instantiateStreaming(response, imports);
-#if USE_OFFSET_CONVERTER
-      // When using the offset converter, we must interpose here. First,
-      // the instantiation result must arrive (if it fails, the error
-      // handling later down will handle it). Once it arrives, we can
-      // initialize the offset converter. And only then is it valid to
-      // call receiveInstantiationResult, as that function will use the
-      // offset converter (in the case of pthreads, it will create the
-      // pthreads and send them the offsets along with the wasm instance).
-      var arrayBufferResult = await clonedResponse.arrayBuffer();
-      try {
-        wasmOffsetConverter = new WasmOffsetConverter(new Uint8Array(arrayBufferResult), instantiationResult.module);
-      } catch (reason) {
-        err(`failed to initialize offset-converter: ${reason}`);
-      }
-#endif
       return instantiationResult;
     } catch (reason) {
       // We expect the most common failure cause to be a bad MIME type for the binary,

src/runtime_common.js

@@ -60,11 +60,6 @@ var wasmSourceMap;
 #include "source_map_support.js"
 #endif
 
-#if USE_OFFSET_CONVERTER
-var wasmOffsetConverter;
-#include "wasm_offset_converter.js"
-#endif
-
 // Memory management
 
 #if !WASM_ESM_INTEGRATION || IMPORTED_MEMORY

src/runtime_pthread.js

@@ -26,7 +26,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
   // Thread-local guard variable for one-time init of the JS state
   var initializedJS = false;
 
-#if LOAD_SOURCE_MAP || USE_OFFSET_CONVERTER
+#if LOAD_SOURCE_MAP
   // When using postMessage to send an object, it is processed by the structured
   // clone algorithm.  The prototype, and hence methods, on that object is then
   // lost. This function adds back the lost prototype.  This does not work with
@@ -112,9 +112,6 @@ if (ENVIRONMENT_IS_PTHREAD) {
 #if LOAD_SOURCE_MAP
         wasmSourceMap = resetPrototype(WasmSourceMap, msgData.wasmSourceMap);
 #endif
-#if USE_OFFSET_CONVERTER
-        wasmOffsetConverter = resetPrototype(WasmOffsetConverter, msgData.wasmOffsetConverter);
-#endif
 
 #if !WASM_ESM_INTEGRATION
 #if MINIMAL_RUNTIME