runtime: handle kindString in cgoCheckArg

It's awkward to get a string value in cgoCheckArg, but SWIG testing
revealed that it is possible.  The new handling of extra files in the
ptr.go test emulates what SWIG does with an exported function that
returns a string.

Change-Id: I453717f867b8a49499576c28550e7c93053a0cf8
Reviewed-on: https://go-review.googlesource.com/19020
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/errors/ptr.go

@@ -27,10 +27,16 @@ type ptrTest struct {
 	imports   []string // a list of imports
 	support   string   // supporting functions
 	body      string   // the body of the main function
+	extra     []extra  // extra files
 	fail      bool     // whether the test should fail
 	expensive bool     // whether the test requires the expensive check
 }
 
+type extra struct {
+	name     string
+	contents string
+}
+
 var ptrTests = []ptrTest{
 	{
 		// Passing a pointer to a struct that contains a Go pointer.
@@ -237,6 +243,43 @@ var ptrTests = []ptrTest{
                           func GoFn() *byte { return (*byte)(C.malloc(1)) }`,
 		body: `C.GoFn()`,
 	},
+	{
+		// Passing a Go string is fine.
+		name: "pass-string",
+		c: `#include <stddef.h>
+                    typedef struct { const char *p; ptrdiff_t n; } gostring;
+                    gostring f(gostring s) { return s; }`,
+		imports: []string{"unsafe"},
+		body:    `s := "a"; r := C.f(*(*C.gostring)(unsafe.Pointer(&s))); if *(*string)(unsafe.Pointer(&r)) != s { panic(r) }`,
+	},
+	{
+		// Passing a slice of Go strings fails.
+		name:    "pass-string-slice",
+		c:       `void f(void *p) {}`,
+		imports: []string{"strings", "unsafe"},
+		support: `type S struct { a [1]string }`,
+		body:    `s := S{a:[1]string{strings.Repeat("a", 2)}}; C.f(unsafe.Pointer(&s.a[0]))`,
+		fail:    true,
+	},
+	{
+		// Exported functions may not return strings.
+		name:    "ret-string",
+		c:       `extern void f();`,
+		imports: []string{"strings"},
+		support: `//export GoStr
+                          func GoStr() string { return strings.Repeat("a", 2) }`,
+		body: `C.f()`,
+		extra: []extra{
+			{
+				"call.c",
+				`#include <stddef.h>
+                                 typedef struct { const char *p; ptrdiff_t n; } gostring;
+                                 extern gostring GoStr();
+                                 void f() { GoStr(); }`,
+			},
+		},
+		fail: true,
+	},
 }
 
 func main() {
@@ -244,12 +287,17 @@ func main() {
 }
 
 func doTests() int {
-	dir, err := ioutil.TempDir("", "cgoerrors")
+	gopath, err := ioutil.TempDir("", "cgoerrors")
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		return 2
 	}
-	defer os.RemoveAll(dir)
+	defer os.RemoveAll(gopath)
+
+	if err := os.MkdirAll(filepath.Join(gopath, "src"), 0777); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return 2
+	}
 
 	workers := runtime.NumCPU() + 1
 
@@ -259,7 +307,7 @@ func doTests() int {
 	for i := 0; i < workers; i++ {
 		wg.Add(1)
 		go func() {
-			worker(dir, c, errs)
+			worker(gopath, c, errs)
 			wg.Done()
 		}()
 	}
@@ -281,10 +329,10 @@ func doTests() int {
 	return tot
 }
 
-func worker(dir string, c, errs chan int) {
+func worker(gopath string, c, errs chan int) {
 	e := 0
 	for i := range c {
-		if !doOne(dir, i) {
+		if !doOne(gopath, i) {
 			e++
 		}
 	}
@@ -293,9 +341,15 @@ func worker(dir string, c, errs chan int) {
 	}
 }
 
-func doOne(dir string, i int) bool {
+func doOne(gopath string, i int) bool {
 	t := &ptrTests[i]
 
+	dir := filepath.Join(gopath, "src", fmt.Sprintf("dir%d", i))
+	if err := os.Mkdir(dir, 0777); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return false
+	}
+
 	name := filepath.Join(dir, fmt.Sprintf("t%d.go", i))
 	f, err := os.Create(name)
 	if err != nil {
@@ -330,13 +384,30 @@ func doOne(dir string, i int) bool {
 		return false
 	}
 	if err := f.Close(); err != nil {
-		fmt.Fprintln(os.Stderr, "closing %s: %v\n", name, err)
+		fmt.Fprintf(os.Stderr, "closing %s: %v\n", name, err)
 		return false
 	}
 
+	for _, e := range t.extra {
+		if err := ioutil.WriteFile(filepath.Join(dir, e.name), []byte(e.contents), 0644); err != nil {
+			fmt.Fprintf(os.Stderr, "writing %s: %v\n", e.name, err)
+			return false
+		}
+	}
+
 	ok := true
 
-	cmd := exec.Command("go", "run", name)
+	cmd := exec.Command("go", "build")
+	cmd.Dir = dir
+	cmd.Env = addEnv("GOPATH", gopath)
+	buf, err := cmd.CombinedOutput()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "test %s failed to build: %v\n%s", t.name, err, buf)
+		return false
+	}
+
+	exe := filepath.Join(dir, filepath.Base(dir))
+	cmd = exec.Command(exe)
 	cmd.Dir = dir
 
 	if t.expensive {
@@ -354,7 +425,7 @@ func doOne(dir string, i int) bool {
 			ok = false
 		}
 
-		cmd = exec.Command("go", "run", name)
+		cmd = exec.Command(exe)
 		cmd.Dir = dir
 	}
 
@@ -362,7 +433,7 @@ func doOne(dir string, i int) bool {
 		cmd.Env = cgocheckEnv("2")
 	}
 
-	buf, err := cmd.CombinedOutput()
+	buf, err = cmd.CombinedOutput()
 
 	if t.fail {
 		if err == nil {
@@ -389,7 +460,7 @@ func doOne(dir string, i int) bool {
 
 		if !t.expensive && ok {
 			// Make sure it passes with the expensive checks.
-			cmd := exec.Command("go", "run", name)
+			cmd := exec.Command(exe)
 			cmd.Dir = dir
 			cmd.Env = cgocheckEnv("2")
 			buf, err := cmd.CombinedOutput()
@@ -404,7 +475,7 @@ func doOne(dir string, i int) bool {
 	}
 
 	if t.fail && ok {
-		cmd = exec.Command("go", "run", name)
+		cmd = exec.Command(exe)
 		cmd.Dir = dir
 		cmd.Env = cgocheckEnv("0")
 		buf, err := cmd.CombinedOutput()
@@ -427,9 +498,14 @@ func reportTestOutput(w io.Writer, name string, buf []byte) {
 }
 
 func cgocheckEnv(val string) []string {
-	env := []string{"GODEBUG=cgocheck=" + val}
+	return addEnv("GODEBUG", "cgocheck="+val)
+}
+
+func addEnv(key, val string) []string {
+	env := []string{key + "=" + val}
+	look := key + "="
 	for _, e := range os.Environ() {
-		if !strings.HasPrefix(e, "GODEBUG=") {
+		if !strings.HasPrefix(e, look) {
 			env = append(env, e)
 		}
 	}

src/runtime/cgocall.go

@@ -467,6 +467,14 @@ func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 			cgoCheckArg(st.elem, p, true, false, msg)
 			p = add(p, st.elem.size)
 		}
+	case kindString:
+		ss := (*stringStruct)(p)
+		if !cgoIsGoPointer(ss.str) {
+			return
+		}
+		if !top {
+			panic(errorString(msg))
+		}
 	case kindStruct:
 		st := (*structtype)(unsafe.Pointer(t))
 		if !indir {