finalize: Strip "em_js" named data segment.

If we find a data segment with the name "em_js", strip it from the
binary.  Even in debug mode the names given to data segments by clang
will always start with ".data." or ".rodata" so there is no risk of
normal data ending up in a section with this name.

See: emscripten-core/emscripten#13443

Author: sbc100

src/wasm/wasm-emscripten.cpp

@@ -413,6 +413,12 @@ EmJsWalker fixEmJsFuncsAndReturnWalker(Module& wasm) {
     wasm.removeExport(exp.name);
     wasm.removeFunction(exp.value);
   }
+  for (auto iter = wasm.memory.segments.begin(); iter != wasm.memory.segments.end(); iter++) {
+    if (iter->name == "em_js") {
+      wasm.memory.segments.erase(iter);
+      break;
+    }
+  }
   return walker;
 }
 

test/lit/wasm-emscripten-finalize/em_js.wat

@@ -6,17 +6,27 @@
 ;; Both functions should be stripped from the binary
 ;; CHECK-NOT:  (func
 
+;; The data section names "em_js" should be stripped.
+;; CHECK-NOT: (i32.const 512) "JS string in named section\00")
+
+;; Other data sections should not be stripped
+;; CHECK: (data (i32.const 1024) "some JS string data\00")
+;; CHECK: (data (i32.const 2048) "more JS string data\00")
+
 ;;      CHECK:  "emJsFuncs": {
-;; CHECK-NEXT:    "bar": "more JS string dara",
-;; CHECK-NEXT:    "foo": "some JS string"
+;; CHECK-NEXT:    "bar": "more JS string data",
+;; CHECK-NEXT:    "baz": "JS string in named section"
+;; CHECK-NEXT:    "foo": "some JS string data"
 ;; CHECK-NEXT:  },
 
 (module
  (memory 1 1)
- (data (i32.const 1024) "some JS string\00")
- (data (i32.const 2048) "more JS string dara\00")
+ (data $em_js (i32.const 512) "JS string in named section\00")
+ (data (i32.const 1024) "some JS string data\00")
+ (data (i32.const 2048) "more JS string data\00")
  (export "__em_js__foo" (func $__em_js__foo))
  (export "__em_js__bar" (func $bar))
+ (export "__em_js__baz" (func $__em_js__baz))
  ;; Name matches export name
  (func $__em_js__foo (result i32)
   (i32.const 1024)
@@ -25,4 +35,8 @@
  (func $bar (result i32)
   (i32.const 2048)
  )
+ ;; Data in "em_js" named section
+ (func $__em_js__baz (result i32)
+  (i32.const 512)
+ )
 )