cgen,dl: remove workaround in dl, generate a DllMain() in cgen instead for -shared on windows (#23961)

vlib/dl/dl_windows.c.v

@@ -20,25 +20,11 @@ type FN_vcleanup_caller = fn ()
 // open loads a given module into the address space of the calling process.
 pub fn open(filename string, flags int) voidptr {
 	res := C.LoadLibrary(filename.to_wide())
-	// Because LoadLibrary has no constructor, this is a workaround
-	if !isnil(res) {
-		vinit_caller := FN_vinit_caller(sym(res, '_vinit_caller'))
-		if !isnil(vinit_caller) {
-			vinit_caller()
-		}
-	}
 	return res
 }
 
 // close frees the loaded a given module.
 pub fn close(handle voidptr) bool {
-	// Because FreeLibrary has no destructor, this is a workaround
-	if !isnil(handle) {
-		vcleanup_caller := FN_vcleanup_caller(sym(handle, '_vcleanup_caller'))
-		if !isnil(vcleanup_caller) {
-			vcleanup_caller()
-		}
-	}
 	return C.FreeLibrary(handle)
 }
 

vlib/v/gen/c/cgen.v

@@ -1082,6 +1082,9 @@ pub fn (mut g Gen) finish() {
 	g.handle_embedded_files_finish()
 	if g.pref.is_test {
 		g.gen_c_main_for_tests()
+	} else if (g.pref.is_shared || g.pref.is_liveshared) && g.pref.os == .windows {
+		// create DllMain() for windows .dll
+		g.gen_dll_main()
 	} else {
 		g.gen_c_main()
 	}

vlib/v/gen/c/cmain.v

@@ -392,3 +392,33 @@ pub fn (mut g Gen) gen_c_main_trace_calls_hook() {
 	should_trace_c_main := g.pref.should_trace_fn_name('C.main')
 	g.writeln('\tu8 bottom_of_stack = 0; g_stack_base = &bottom_of_stack; v__trace_calls__on_c_main(${should_trace_c_main});')
 }
+
+// gen_dll_main create DllMain() for windows .dll
+pub fn (mut g Gen) gen_dll_main() {
+	g.writeln('VV_EXPORTED_SYMBOL BOOL DllMain(HINSTANCE hinst,DWORD fdwReason,LPVOID lpvReserved) {
+	switch (fdwReason) {
+		case DLL_PROCESS_ATTACH : {
+#if defined(_VGCBOEHM)
+			GC_set_pages_executable(0);
+			GC_INIT();
+#endif
+			_vinit_caller();
+			break;
+		}
+		case DLL_THREAD_ATTACH : {
+			break;
+		}
+		case DLL_THREAD_DETACH : {
+			break;
+		}
+		case DLL_PROCESS_DETACH : {
+			_vcleanup_caller();
+			break;
+		}
+		default:
+			return false;
+	}
+	return true;
+}
+	')
+}

vlib/v/gen/c/testdata/closure_shared_lib.c.must_have

@@ -1,2 +1 @@
-__closure_init(); // vinit_caller()
+__closure_init(); // vinit_caller()
-__closure_init(); // main()

vlib/v/tests/create_dll/create_win_dll.c.v

@@ -9,23 +9,3 @@ const bar = (foo << 5) + 9
 pub fn test_tatltuae() int {
 	return foo + bar
 }
-
-@[callconv: stdcall]
-@[export: DllMain]
-fn main(hinst voidptr, fdw_reason int, lp_reserved voidptr) bool {
-	match fdw_reason {
-		C.DLL_PROCESS_ATTACH {
-			$if static_boehm ? {
-				C.GC_INIT()
-			}
-			C._vinit(0, 0)
-		}
-		C.DLL_THREAD_ATTACH {}
-		C.DLL_THREAD_DETACH {}
-		C.DLL_PROCESS_DETACH {}
-		else {
-			return false
-		}
-	}
-	return true
-}