Enable EM_ASM in side modules (#18228)

The only way I could find to make work was to use `eval`.  Sadly even
using `new Function` didn't work since it evaluates the code not in the
containing (module) scope but in the global scope.

Depends on WebAssembly/binaryen#5274

Fixes: #18199

Author: sbc100

emcc.py

@@ -607,6 +607,8 @@ def get_binaryen_passes():
     passes += ['--signext-lowering']
   if optimizing:
     passes += ['--post-emscripten']
+    if settings.SIDE_MODULE:
+      passes += ['--pass-arg=post-emscripten-side-module']
   if optimizing:
     passes += [building.opt_level_to_str(settings.OPT_LEVEL, settings.SHRINK_LEVEL)]
   # when optimizing, use the fact that low memory is never used (1024 is a

emscripten.py

@@ -337,8 +337,6 @@ def emscript(in_wasm, out_wasm, outfile_js, memfile):
           diagnostics.warning('em-js-i64', 'using 64-bit arguments in EM_JS function without WASM_BIGINT is not yet fully supported: `%s` (%s, %s)', em_js_func, c_sig, signature.params)
 
   if settings.SIDE_MODULE:
-    if metadata.asmConsts:
-      exit_with_error('EM_ASM is not supported in side modules')
     if metadata.emJsFuncs:
       exit_with_error('EM_JS is not supported in side modules')
     logger.debug('emscript: skipping remaining js glue generation')

site/source/docs/compiling/Dynamic-Linking.rst

@@ -212,6 +212,10 @@ Limitations
    startup
    `[doc] <https://emscripten.org/docs/porting/files/packaging_files.html#preloading-files>`__
    `[discuss] <https://groups.google.com/forum/#!topic/emscripten-discuss/cE3hUV3fDSw>`__.
+- ``EM_ASM`` code defined within side modules depends on ``eval`` support are
+  is therefore incompatible with ``-sDYNAMIC_EXECUTION=0``.
+- ``EM_JS`` functions defined in side modules are not yet supported.
+
 
 Pthreads support
 ----------------

src/library_dylink.js

@@ -89,6 +89,8 @@ var LibraryDylink = {
       '_emscripten_tls_init',
       '__wasm_init_tls',
       '__wasm_call_ctors',
+      '__start_em_asm',
+      '__stop_em_asm',
     ].includes(symName)
 #if SPLIT_MODULE
         // Exports synthesized by wasm-split should be prefixed with '%'
@@ -657,6 +659,39 @@ var LibraryDylink = {
         }
 #endif
 
+#if MAIN_MODULE
+        function addEmAsm(addr, body) {
+          var args = [];
+          var arity = 0;
+          for (; arity < 16; arity++) {
+            if (body.indexOf('$' + arity) != -1) {
+              args.push('$' + arity);
+            } else {
+              break;
+            }
+          }
+          args = args.join(',');
+          var func = '(' + args +' ) => { ' + body + '};'
+#if DYLINK_DEBUG
+          dbg('adding new EM_ASM constant at: ' + ptrToString(start));
+#endif
+          {{{ makeEval('ASM_CONSTS[start] = eval(func)') }}};
+        }
+
+        // Add any EM_ASM function that exist in the side module
+        if ('__start_em_asm' in moduleExports) {
+          var start = moduleExports['__start_em_asm'];
+          var stop = moduleExports['__stop_em_asm'];
+          {{{ from64('start') }}}
+          {{{ from64('stop') }}}
+          while (start < stop) {
+            var jsString = UTF8ToString(start);
+            addEmAsm(start, jsString);
+            start = HEAPU8.indexOf(0, start) + 1;
+          }
+        }
+#endif
+
         // initialize the module
 #if USE_PTHREADS
         // Only one thread (currently The main thread) should call

src/settings.js

@@ -1251,12 +1251,13 @@ var BENCHMARK = false;
 // [link]
 var EXPORT_NAME = 'Module';
 
-// When set to 0, we do not emit eval() and new Function(), which disables some functionality
-// (causing runtime errors if attempted to be used), but allows the emitted code to be
-// acceptable in places that disallow dynamic code execution (chrome packaged app,
-// privileged firefox app, etc.). Pass this flag when developing an Emscripten application
-// that is targeting a privileged or a certified execution environment, see
-// Firefox Content Security Policy (CSP) webpage for details:
+// When set to 0, we do not emit eval() and new Function(), which disables some
+// functionality (causing runtime errors if attempted to be used), but allows
+// the emitted code to be acceptable in places that disallow dynamic code
+// execution (chrome packaged app, privileged firefox app, etc.). Pass this flag
+// when developing an Emscripten application that is targeting a privileged or a
+// certified execution environment, see Firefox Content Security Policy (CSP)
+// webpage for details:
 // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src
 // in particular the 'unsafe-eval' and 'wasm-unsafe-eval' policies.
 //
@@ -1271,11 +1272,12 @@ var EXPORT_NAME = 'Module';
 // - emscripten_run_script_int(),
 // - emscripten_run_script_string(),
 // - dlopen(),
-// - the functions ccall() and cwrap() are still available, but they are restricted to only
-//   being able to call functions that have been exported in the Module object in advance.
+// - the functions ccall() and cwrap() are still available, but they are
+//   restricted to only being able to call functions that have been exported in
+//   the Module object in advance.
 //
-// When set to -sDYNAMIC_EXECUTION=2 flag is set, attempts to call to eval() are demoted
-// to warnings instead of throwing an exception.
+// When -sDYNAMIC_EXECUTION=2 is set, attempts to call to eval() are demoted to
+// warnings instead of throwing an exception.
 // [link]
 var DYNAMIC_EXECUTION = 1;
 

test/core/test_em_asm_main.c

@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <emscripten.h>
+
+int test_side();
+
+int main() {
+  printf("in main\n");
+  EM_ASM(out("em_asm in main"));
+  return test_side();
+}

test/core/test_em_asm_main.out

@@ -0,0 +1,17 @@
+in main
+em_asm in main
+no args works
+int types:
+         char : 1
+  signed char : 2
+unsigned char : 3
+         short: 4
+  signed short: 5
+unsigned short: 6
+         int  : 7
+  signed int  : 8
+unsigned int  : 9
+         long : 10
+  signed long : 11
+unsigned long : 12
+    terminator: 42

test/core/test_em_asm_side.c

@@ -0,0 +1,28 @@
+#include <emscripten.h>
+#include <stdio.h>
+
+int test_side() {
+  EM_ASM(out("no args works"));
+
+  EM_ASM({
+    console.log("int types:");
+    out("         char : " + $0);
+    out("  signed char : " + $1);
+    out("unsigned char : " + $2);
+    out("         short: " + $3);
+    out("  signed short: " + $4);
+    out("unsigned short: " + $5);
+    out("         int  : " + $6);
+    out("  signed int  : " + $7);
+    out("unsigned int  : " + $8);
+    out("         long : " + $9);
+    out("  signed long : " + $10);
+    out("unsigned long : " + $11);
+    out("    terminator: " + $12);
+  }, (char)1, (signed char)2, (unsigned char)3,
+     (short)4, (signed short)5, (unsigned short)6,
+     (int)7, (signed int)8, (unsigned int)9,
+     (long)10, (signed long)11, (unsigned long)12, 42);
+
+  return 0;
+}

test/test_core.py

@@ -2257,6 +2257,11 @@ def test_em_asm_arguments_side_effects(self):
   def test_em_asm_direct(self):
     self.do_core_test('test_em_asm_direct.c')
 
+  @needs_dylink
+  def test_em_asm_side_module(self):
+    self.build(test_file('core/test_em_asm_side.c'), js_outfile=False, emcc_args=['-sSIDE_MODULE'], output_basename='side')
+    self.do_core_test('test_em_asm_main.c', emcc_args=['-sMAIN_MODULE=2', 'side.wasm'])
+
   @parameterized({
     '': ([], False),
     'pthreads': (['-sUSE_PTHREADS', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME'], False),

test/test_other.py

@@ -11645,10 +11645,6 @@ def test_runtime_keepalive(self):
     self.set_setting('EXIT_RUNTIME')
     self.do_other_test('test_runtime_keepalive.cpp')
 
-  def test_em_asm_side_module(self):
-    err = self.expect_fail([EMCC, '-sSIDE_MODULE', test_file('hello_world_em_asm.c')])
-    self.assertContained('EM_ASM is not supported in side modules', err)
-
   def test_em_js_side_module(self):
     err = self.expect_fail([EMXX, '-sSIDE_MODULE', test_file('core/test_em_js.cpp')])
     self.assertContained('EM_JS is not supported in side modules', err)