cmd/compile: note escape of parts of closured-capture vars

Missed a case for closure calls (OCALLFUNC && indirect) in
esc.go:esccall.

Cleanup to runtime code for windows to more thoroughly hide
a technical escape.  Also made code pickier about failing
to late non-optional kernel32.dll.

Fixes #14409.

Change-Id: Ie75486a2c8626c4583224e02e4872c2875f7bca5
Reviewed-on: https://go-review.googlesource.com/20102
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/esc.go

@@ -1458,6 +1458,11 @@ func esccall(e *EscState, n *Node, up *Node) {
 			if haspointers(t.Type) {
 				escassignSinkNilWhy(e, n, src, "receiver in indirect call")
 			}
+		} else { // indirect and OCALLFUNC = could be captured variables, too. (#14409)
+			ll := e.nodeEscState(n).Escretval.Slice()
+			for _, llN := range ll {
+				escassignDereference(e, llN, fn, e.stepAssign(nil, llN, fn, "captured by called closure"))
+			}
 		}
 		return
 	}

src/runtime/os1_windows.go

@@ -110,23 +110,28 @@ func asmstdcall(fn unsafe.Pointer)
 
 var asmstdcallAddr unsafe.Pointer
 
-func loadOptionalSyscalls() {
-	var buf [50]byte // large enough for longest string
-	strtoptr := func(s string) uintptr {
-		buf[copy(buf[:], s)] = 0 // nil-terminated for OS
-		return uintptr(noescape(unsafe.Pointer(&buf[0])))
-	}
-	l := stdcall1(_LoadLibraryA, strtoptr("kernel32.dll"))
-	findfunc := func(name string) stdFunction {
-		f := stdcall2(_GetProcAddress, l, strtoptr(name))
+func windowsFindfunc(name []byte, lib uintptr) stdFunction {
+	f := stdcall2(_GetProcAddress, lib, uintptr(unsafe.Pointer(&name[0])))
 	return stdFunction(unsafe.Pointer(f))
+}
+
+func loadOptionalSyscalls() {
+	var (
+		kernel32dll                 = []byte("kernel32.dll\000")
+		addVectoredContinueHandler  = []byte("AddVectoredContinueHandler\000")
+		getQueuedCompletionStatusEx = []byte("GetQueuedCompletionStatusEx\000")
+		addDllDirectory             = []byte("AddDllDirectory\000")
+		loadLibraryExW              = []byte("LoadLibraryExW\000")
+	)
+
+	k32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&kernel32dll[0])))
+	if k32 == 0 {
+		throw("kernel32.dll not found")
 	}
-	if l != 0 {
-		_AddDllDirectory = findfunc("AddDllDirectory")
-		_AddVectoredContinueHandler = findfunc("AddVectoredContinueHandler")
-		_GetQueuedCompletionStatusEx = findfunc("GetQueuedCompletionStatusEx")
-		_LoadLibraryExW = findfunc("LoadLibraryExW")
-	}
+	_AddDllDirectory = windowsFindfunc(addDllDirectory, k32)
+	_AddVectoredContinueHandler = windowsFindfunc(addVectoredContinueHandler, k32)
+	_GetQueuedCompletionStatusEx = windowsFindfunc(getQueuedCompletionStatusEx, k32)
+	_LoadLibraryExW = windowsFindfunc(loadLibraryExW, k32)
 }
 
 //go:nosplit

test/escape_closure.go

@@ -145,3 +145,29 @@ func ClosureCallArgs15() {
 		// BAD: p should not escape here
 	}(&p) // ERROR "&p escapes to heap" "\(func literal\)\(&p\) escapes to heap"
 }
+
+func ClosureLeak1(s string) string { // ERROR "ClosureLeak1 s does not escape"
+	t := s + "YYYY"         // ERROR "escapes to heap"
+	return ClosureLeak1a(t) // ERROR "ClosureLeak1 ... argument does not escape"
+}
+
+// See #14409 -- returning part of captured var leaks it.
+func ClosureLeak1a(a ...string) string { // ERROR "leaking param: a to result ~r1 level=1"
+	return func() string { // ERROR "ClosureLeak1a func literal does not escape"
+		return a[0]
+	}()
+}
+
+func ClosureLeak2(s string) string { // ERROR "ClosureLeak2 s does not escape"
+	t := s + "YYYY"       // ERROR "escapes to heap"
+	c := ClosureLeak2a(t) // ERROR "ClosureLeak2 ... argument does not escape"
+	return c
+}
+func ClosureLeak2a(a ...string) string { // ERROR "leaking param: a to result ~r1 level=1"
+	return ClosureLeak2b(func() string { // ERROR "ClosureLeak2a func literal does not escape"
+		return a[0]
+	})
+}
+func ClosureLeak2b(f func() string) string { // ERROR "leaking param: f to result ~r1 level=1"
+	return f()
+}