cgen, dl: add windows dll support, fix (#20447)

examples/dynamic_library_loader/modules/library/library.v

@@ -10,7 +10,9 @@ module library
 // `library__add_1`, if not for the export: tag).
 @[export: 'add_1']
 pub fn add_1(x int, y int) int {
-	return my_private_function(x + y)
+	num := my_private_function(x + y)
+	println('hello from ${@FN} , num = ${num}')
+	return num
 }
 
 // this function is not exported and will not be visible to external programs.

examples/dynamic_library_loader/use_test.v

@@ -1,7 +1,5 @@
 module main
 
-// vtest flaky: true
-// vtest retry: 3
 import os
 import dl
 
@@ -31,6 +29,7 @@ fn test_can_compile_main_program() {
 	assert os.is_file(library_file_path)
 	result := v_compile('run use_shared_library.v')
 	// dump(result)
+	assert result.output.contains('hello from add_1 , num = 4')
 	assert result.output.contains('res: 4')
 	os.rm(library_file_path) or {}
 }

vlib/dl/dl_windows.c.v

@@ -13,14 +13,32 @@ fn C.GetProcAddress(handle voidptr, procname &u8) voidptr
 
 fn C.FreeLibrary(handle voidptr) bool
 
+type FN_vinit_caller = fn ()
+
+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

@@ -5914,8 +5914,9 @@ fn (mut g Gen) write_init_function() {
 		g.writeln('\tv__trace_calls__on_call(_SLIT("_vinit"));')
 	}
 
-	if g.use_segfault_handler {
+	if g.use_segfault_handler && !g.pref.is_shared {
 		// 11 is SIGSEGV. It is hardcoded here, to avoid FreeBSD compilation errors for trivial examples.
+		// shared object does not need this
 		g.writeln('#if __STDC_HOSTED__ == 1\n\tsignal(11, v_segmentation_fault_handler);\n#endif')
 	}
 	if g.pref.is_bare {
@@ -5930,7 +5931,10 @@ fn (mut g Gen) write_init_function() {
 	// calling module init functions too, just in case they do fail...
 	g.write('\tas_cast_type_indexes = ')
 	g.writeln(g.as_cast_name_table())
-	g.writeln('\tbuiltin_init();')
+	if !g.pref.is_shared {
+		// shared object does not need this
+		g.writeln('\tbuiltin_init();')
+	}
 
 	if g.nr_closures > 0 {
 		g.writeln('\t_closure_mtx_init();')
@@ -6022,19 +6026,30 @@ fn (mut g Gen) write_init_function() {
 		println(g.out.after(fn_vcleanup_start_pos))
 	}
 
-	needs_constructor := g.pref.is_shared && g.pref.os != .windows
-	if needs_constructor {
+	if g.pref.is_shared {
 		// shared libraries need a way to call _vinit/2. For that purpose,
 		// provide a constructor/destructor pair, ensuring that all constants
 		// are initialized just once, and that they will be freed too.
 		// Note: os.args in this case will be [].
-		g.writeln('__attribute__ ((constructor))')
+		if g.pref.os == .windows {
+			g.writeln('// workaround for windows, export _vinit_caller, let dl.open() call it')
+			g.writeln('// NOTE: This is hardcoded in vlib/dl/dl_windows.c.v!')
+			g.writeln('VV_EXPORTED_SYMBOL void _vinit_caller();')
+		} else {
+			g.writeln('__attribute__ ((constructor))')
+		}
 		g.writeln('void _vinit_caller() {')
 		g.writeln('\tstatic bool once = false; if (once) {return;} once = true;')
 		g.writeln('\t_vinit(0,0);')
 		g.writeln('}')
 
-		g.writeln('__attribute__ ((destructor))')
+		if g.pref.os == .windows {
+			g.writeln('// workaround for windows, export _vcleanup_caller, let dl.close() call it')
+			g.writeln('// NOTE: This is hardcoded in vlib/dl/dl_windows.c.v!')
+			g.writeln('VV_EXPORTED_SYMBOL void _vcleanup_caller();')
+		} else {
+			g.writeln('__attribute__ ((destructor))')
+		}
 		g.writeln('void _vcleanup_caller() {')
 		g.writeln('\tstatic bool once = false; if (once) {return;} once = true;')
 		g.writeln('\t_vcleanup();')