{net,os/user,plugin}: eliminate unnecessary C round-trips

We're making two extra round-trips to C to malloc and free strings
that originate in Go and don't escape. Skip those round-trips by
allocating null-terminated slices in Go memory instead.

Change-Id: I9e4c5ad999a7924ba50b82293c52073ec75518be
Reviewed-on: https://go-review.googlesource.com/56530
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/cgo_unix.go

@@ -12,7 +12,6 @@ package net
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netdb.h>
-#include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 */
@@ -95,15 +94,14 @@ func cgoLookupPort(ctx context.Context, network, service string) (port int, err
 }
 
 func cgoLookupServicePort(hints *C.struct_addrinfo, network, service string) (port int, err error) {
-	s := C.CString(service)
-	// Lowercase the service name in the C-allocated memory.
-	for i := 0; i < len(service); i++ {
-		bp := (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(s)) + uintptr(i)))
-		*bp = lowerASCII(*bp)
+	cservice := make([]byte, len(service)+1)
+	copy(cservice, service)
+	// Lowercase the C service name.
+	for i, b := range cservice[:len(service)] {
+		cservice[i] = lowerASCII(b)
 	}
 	var res *C.struct_addrinfo
-	defer C.free(unsafe.Pointer(s))
-	gerrno, err := C.getaddrinfo(nil, s, hints, &res)
+	gerrno, err := C.getaddrinfo(nil, (*C.char)(unsafe.Pointer(&cservice[0])), hints, &res)
 	if gerrno != 0 {
 		switch gerrno {
 		case C.EAI_SYSTEM:
@@ -145,10 +143,10 @@ func cgoLookupIPCNAME(name string) (addrs []IPAddr, cname string, err error) {
 	hints.ai_flags = cgoAddrInfoFlags
 	hints.ai_socktype = C.SOCK_STREAM
 
-	h := C.CString(name)
-	defer C.free(unsafe.Pointer(h))
+	h := make([]byte, len(name)+1)
+	copy(h, name)
 	var res *C.struct_addrinfo
-	gerrno, err := C.getaddrinfo(h, nil, &hints, &res)
+	gerrno, err := C.getaddrinfo((*C.char)(unsafe.Pointer(&h[0])), nil, &hints, &res)
 	if gerrno != 0 {
 		switch gerrno {
 		case C.EAI_SYSTEM:

src/os/user/cgo_lookup_unix.go

@@ -52,8 +52,8 @@ func current() (*User, error) {
 func lookupUser(username string) (*User, error) {
 	var pwd C.struct_passwd
 	var result *C.struct_passwd
-	nameC := C.CString(username)
-	defer C.free(unsafe.Pointer(nameC))
+	nameC := make([]byte, len(username)+1)
+	copy(nameC, username)
 
 	buf := alloc(userBuffer)
 	defer buf.free()
@@ -63,7 +63,7 @@ func lookupUser(username string) (*User, error) {
 		// passing a size_t to getpwnam_r, because for unknown
 		// reasons passing a size_t to getpwnam_r doesn't work on
 		// Solaris.
-		return syscall.Errno(C.mygetpwnam_r(nameC,
+		return syscall.Errno(C.mygetpwnam_r((*C.char)(unsafe.Pointer(&nameC[0])),
 			&pwd,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),
@@ -140,11 +140,11 @@ func lookupGroup(groupname string) (*Group, error) {
 
 	buf := alloc(groupBuffer)
 	defer buf.free()
-	cname := C.CString(groupname)
-	defer C.free(unsafe.Pointer(cname))
+	cname := make([]byte, len(groupname)+1)
+	copy(cname, groupname)
 
 	err := retryWithBuffer(buf, func() syscall.Errno {
-		return syscall.Errno(C.mygetgrnam_r(cname,
+		return syscall.Errno(C.mygetgrnam_r((*C.char)(unsafe.Pointer(&cname[0])),
 			&grp,
 			(*C.char)(buf.ptr),
 			C.size_t(buf.size),

src/os/user/listgroups_unix.go

@@ -15,7 +15,6 @@ import (
 /*
 #include <unistd.h>
 #include <sys/types.h>
-#include <stdlib.h>
 */
 import "C"
 
@@ -25,12 +24,12 @@ func listGroups(u *User) ([]string, error) {
 		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
 	}
 	userGID := C.gid_t(ug)
-	nameC := C.CString(u.Username)
-	defer C.free(unsafe.Pointer(nameC))
+	nameC := make([]byte, len(u.Username)+1)
+	copy(nameC, u.Username)
 
 	n := C.int(256)
 	gidsC := make([]C.gid_t, n)
-	rv := getGroupList(nameC, userGID, &gidsC[0], &n)
+	rv := getGroupList((*C.char)(unsafe.Pointer(&nameC[0])), userGID, &gidsC[0], &n)
 	if rv == -1 {
 		// More than initial buffer, but now n contains the correct size.
 		const maxGroups = 2048
@@ -38,7 +37,7 @@ func listGroups(u *User) ([]string, error) {
 			return nil, fmt.Errorf("user: list groups for %s: member of more than %d groups", u.Username, maxGroups)
 		}
 		gidsC = make([]C.gid_t, n)
-		rv := getGroupList(nameC, userGID, &gidsC[0], &n)
+		rv := getGroupList((*C.char)(unsafe.Pointer(&nameC[0])), userGID, &gidsC[0], &n)
 		if rv == -1 {
 			return nil, fmt.Errorf("user: list groups for %s failed (changed groups?)", u.Username)
 		}

src/plugin/plugin_dlopen.go

@@ -81,16 +81,16 @@ func pathToPrefix(s string) string {
 }
 
 func open(name string) (*Plugin, error) {
-	cPath := (*C.char)(C.malloc(C.PATH_MAX + 1))
-	defer C.free(unsafe.Pointer(cPath))
-
-	cRelName := C.CString(name)
-	defer C.free(unsafe.Pointer(cRelName))
-	if C.realpath(cRelName, cPath) == nil {
+	cPath := make([]byte, C.PATH_MAX+1)
+	cRelName := make([]byte, len(name)+1)
+	copy(cRelName, name)
+	if C.realpath(
+		(*C.char)(unsafe.Pointer(&cRelName[0])),
+		(*C.char)(unsafe.Pointer(&cPath[0]))) == nil {
 		return nil, errors.New("plugin.Open(" + name + "): realpath failed")
 	}
 
-	filepath := C.GoString(cPath)
+	filepath := C.GoString((*C.char)(unsafe.Pointer(&cPath[0])))
 
 	pluginsMu.Lock()
 	if p := plugins[filepath]; p != nil {
@@ -99,7 +99,7 @@ func open(name string) (*Plugin, error) {
 		return p, nil
 	}
 	var cErr *C.char
-	h := C.pluginOpen(cPath, &cErr)
+	h := C.pluginOpen((*C.char)(unsafe.Pointer(&cPath[0])), &cErr)
 	if h == 0 {
 		pluginsMu.Unlock()
 		return nil, errors.New("plugin.Open: " + C.GoString(cErr))
@@ -127,9 +127,11 @@ func open(name string) (*Plugin, error) {
 	plugins[filepath] = p
 	pluginsMu.Unlock()
 
-	initStr := C.CString(pluginpath + ".init")
-	initFuncPC := C.pluginLookup(h, initStr, &cErr)
-	C.free(unsafe.Pointer(initStr))
+	initStr := make([]byte, len(pluginpath)+6)
+	copy(initStr, pluginpath)
+	copy(initStr[len(pluginpath):], ".init")
+
+	initFuncPC := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&initStr[0])), &cErr)
 	if initFuncPC != nil {
 		initFuncP := &initFuncPC
 		initFunc := *(*func())(unsafe.Pointer(&initFuncP))
@@ -144,9 +146,12 @@ func open(name string) (*Plugin, error) {
 			delete(syms, symName)
 			symName = symName[1:]
 		}
-		cname := C.CString(pathToPrefix(pluginpath) + "." + symName)
-		p := C.pluginLookup(h, cname, &cErr)
-		C.free(unsafe.Pointer(cname))
+
+		fullName := pathToPrefix(pluginpath) + "." + symName
+		cname := make([]byte, len(fullName)+1)
+		copy(cname, fullName)
+
+		p := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&cname[0])), &cErr)
 		if p == nil {
 			return nil, errors.New("plugin.Open: could not find symbol " + symName + ": " + C.GoString(cErr))
 		}