[dylink] Fix multiple loading of the same library with RTLD_LOCAL (#20210)

When a library is loaded for a second time we were only handling the
RTLD_GLOBAL case.

Fixes: #20203

Author: sbc100

src/library_dylink.js

@@ -959,15 +959,18 @@ var LibraryDylink = {
     var dso = LDSO.loadedLibsByName[libName];
     if (dso) {
       // the library is being loaded or has been loaded already.
-      //
-      // however it could be previously loaded only locally and if we get
-      // load request with global=true we have to make it globally visible now.
-      if (flags.global && !dso.global) {
-        dso.global = true;
-        if (dso.exports !== 'loading') {
-          // ^^^ if module is 'loading' - symbols merging will be eventually done by the loader.
-          mergeLibSymbols(dso.exports, libName)
+#if ASSERTIONS
+      assert(dso.exports !== 'loading', `Attempt to load '${libName}' twice before the first load completed`);
+#endif
+      if (!flags.global) {
+        if (localScope) {
+          Object.assign(localScope, dso.exports);
         }
+      } else if (!dso.global) {
+        // The library was previously loaded only locally but not
+        // we have a request with global=true.
+        dso.global = true;
+        mergeLibSymbols(dso.exports, libName)
       }
       // same for "nodelete"
       if (flags.nodelete && dso.refcount !== Infinity) {

test/test_core.py

@@ -4102,29 +4102,46 @@ def test_dlfcn_asyncify(self):
 
   @needs_dylink
   def test_dlfcn_rtld_local(self):
+    # Create two shared libraries that both depend on a third.
+    #  liba.so -> libsub.so
+    #  libb.so -> libsub.so
     create_file('liba.c', r'''
       #include <stdio.h>
 
-      void func_b();
+      void func_sub();
 
       void func_a() {
         printf("func_a\n");
         // Call a function from a dependent DSO. This symbol should
         // be available here even though liba itself is loaded with RTLD_LOCAL.
-        func_b();
+        func_sub();
       }
       ''')
 
     create_file('libb.c', r'''
       #include <stdio.h>
 
+      void func_sub();
+
       void func_b() {
         printf("func_b\n");
+        // Call a function from a dependent DSO. This symbol should
+        // be available here even though liba itself is loaded with RTLD_LOCAL.
+        func_sub();
+      }
+    ''')
+
+    create_file('libsub.c', r'''
+      #include <stdio.h>
+
+      void func_sub() {
+        printf("func_sub\n");
       }
     ''')
 
-    self.build_dlfcn_lib('libb.c', outfile='libb.so')
-    self.build_dlfcn_lib('liba.c', outfile='liba.so', emcc_args=['libb.so'])
+    self.build_dlfcn_lib('libsub.c', outfile='libsub.so')
+    self.build_dlfcn_lib('libb.c', outfile='libb.so', emcc_args=['libsub.so'])
+    self.build_dlfcn_lib('liba.c', outfile='liba.so', emcc_args=['libsub.so'])
 
     self.prep_dlfcn_main(['liba.so', 'libb.so', '-L.'])
     create_file('main.c', r'''
@@ -4133,28 +4150,41 @@ def test_dlfcn_rtld_local(self):
       #include <stdio.h>
 
       int main() {
+        void* handle;
+        void (*f)();
+
         printf("main\n");
-        void* handle = dlopen("liba.so", RTLD_NOW|RTLD_LOCAL);
+        // Call a function from libb
+        handle = dlopen("liba.so", RTLD_NOW|RTLD_LOCAL);
         assert(handle);
 
-        void (*f)();
         f = dlsym(handle, "func_a");
         assert(f);
         f();
 
-        // Verify that symbols from liba.so and libb.so are not globally
+        // Same for libb
+        handle = dlopen("libb.so", RTLD_NOW|RTLD_LOCAL);
+        assert(handle);
+
+        f = dlsym(handle, "func_b");
+        assert(f);
+        f();
+
+        // Verify that symbols from all three libraries are not globally
         // visible.
-        void* func_a = dlsym(RTLD_DEFAULT, "func_a");
-        assert(func_a == NULL);
-        void* func_b = dlsym(RTLD_DEFAULT, "func_b");
-        assert(func_b == NULL);
+        f = dlsym(RTLD_DEFAULT, "func_a");
+        assert(f == NULL);
+        f = dlsym(RTLD_DEFAULT, "func_b");
+        assert(f == NULL);
+        f = dlsym(RTLD_DEFAULT, "func_sub");
+        assert(f == NULL);
 
         printf("done\n");
         return 0;
       }
       ''')
 
-    self.do_runf('main.c', 'main\nfunc_a\nfunc_b\ndone\n')
+    self.do_runf('main.c', 'main\nfunc_a\nfunc_sub\nfunc_b\nfunc_sub\ndone\n')
 
   def dylink_test(self, main, side, expected=None, header=None, force_c=False,
                   main_module=2, **kwargs):

test/test_other.py

@@ -8339,8 +8339,7 @@ def test_side_module_naming(self):
       self.assertTrue(building.is_wasm_dylib(target))
 
       create_file('main.c', '')
-      self.run_process([EMCC, '-sMAIN_MODULE=2', 'main.c', '-Werror', target])
-      self.run_js('a.out.js')
+      self.do_runf('main.c', emcc_args=['-sMAIN_MODULE=2', 'main.c', '-Werror', target])
 
   def test_side_module_missing(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-sSIDE_MODULE', '-o', 'libside1.wasm'])