Add MUTABLE_GLOBALS to feature_matrix

This is needed by dynamic linking since GOT entries are all imported as
mutable globals.

The net effect of this is that you cannot actually target the oldest
version of safari that we support (12) and with dynamically linked
programs.  Specifying `-sLEGACY_VM_SUPPORT` will give you safari 13.1
instead of 12 if you also using `-sMAIN_MODULE`.

Author: sbc100

src/lib/libdylink.js

@@ -276,12 +276,10 @@ var LibraryDylink = {
         continue;
       }
 #endif
-      if (typeof value?.value != 'undefined') {
-        // a breaking change in the wasm spec, globals are now objects
-        // https://github.com/WebAssembly/mutable-global/issues/1
+      // Detect wasm global exports. These represent data addresses
+      // which are relative to `memoryBase`
+      if (typeof value.value != 'undefined') {
         value = value.value;
-      }
-      if (typeof value == {{{ POINTER_JS_TYPE }}}) {
         value += {{{ to64('memoryBase') }}};
       }
       relocated[e] = value;

test/codesize/test_codesize_hello_dylink.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 26931,
-  "a.out.js.gz": 11472,
+  "a.out.js": 26908,
+  "a.out.js.gz": 11463,
   "a.out.nodebug.wasm": 18567,
   "a.out.nodebug.wasm.gz": 9199,
-  "total": 45498,
-  "total_gz": 20671,
+  "total": 45475,
+  "total_gz": 20662,
   "sent": [
     "__heap_base",
     "__indirect_function_table",

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
-  "a.out.js": 245841,
+  "a.out.js": 245818,
   "a.out.nodebug.wasm": 597746,
-  "total": 843587,
+  "total": 843564,
   "sent": [
     "IMG_Init",
     "IMG_Load",

test/test_other.py

@@ -2015,6 +2015,9 @@ def test_exclude_file(self):
   def test_dylink_strict(self):
     self.do_run_in_out_file_test('hello_world.c', cflags=['-sSTRICT', '-sMAIN_MODULE=1'])
 
+  def test_dylink_legacy(self):
+    self.do_run_in_out_file_test('hello_world.c', cflags=['-sLEGACY_GL_EMULATION', '-sMAIN_MODULE=2'])
+
   def test_dylink_exceptions_and_assertions(self):
     # Linking side modules using the STL and exceptions should not abort with
     # "function in Table but not functionsInTableMap" when using ASSERTIONS=2

tools/feature_matrix.py

@@ -31,6 +31,7 @@
 
 
 class Feature(IntEnum):
+  MUTABLE_GLOBALS = auto()
   NON_TRAPPING_FPTOINT = auto()
   SIGN_EXT = auto()
   BULK_MEMORY = auto()
@@ -48,6 +49,12 @@ class Feature(IntEnum):
 enable_override_features = set()
 
 min_browser_versions = {
+  Feature.MUTABLE_GLOBALS: {
+    'chrome': 74,
+    'firefox': 61,
+    'safari': 130100,
+    'node': 120000,
+  },
   Feature.NON_TRAPPING_FPTOINT: {
     'chrome': 75,
     'firefox': 65,
@@ -213,6 +220,8 @@ def apply_min_browser_versions():
     enable_feature(Feature.BULK_MEMORY, 'pthreads')
   elif settings.WASM_WORKERS or settings.SHARED_MEMORY:
     enable_feature(Feature.BULK_MEMORY, 'shared-mem')
+  if settings.RELOCATABLE:
+    enable_feature(Feature.MUTABLE_GLOBALS, 'dynamic linking')
   if settings.MEMORY64 == 1:
     enable_feature(Feature.MEMORY64, 'MEMORY64')
   if settings.EXPORT_ES6 and settings.PTHREADS: