syscall: replace lstat, lchown, stat to please Android O

Implement Lstat with fstatat and Lchown with Fchownat on
linux/amd64, linux/arm and linux/386. Furthermore, implement Stat
with fstatat on linux/arm and linux/386. Linux/arm64 already had
similar replacements.

The fstatat and fchownat system calls were added in kernel 2.6.16,
which is before the Go minimum, 2.6.23.

The three syscalls then match the android bionic implementation
and avoids the Android O seccomp filter.

Fixes #27797

Change-Id: I07fd5506955d454a1a660fef5af0e1ac1ecb0959
Reviewed-on: https://go-review.googlesource.com/136795
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/syscall_linux_386.go

@@ -62,8 +62,6 @@ func Pipe2(p []int, flags int) (err error) {
 //sysnb	InotifyInit() (fd int, err error)
 //sys	Ioperm(from int, num int, on int) (err error)
 //sys	Iopl(level int) (err error)
-//sys	Lchown(path string, uid int, gid int) (err error) = SYS_LCHOWN32
-//sys	Lstat(path string, stat *Stat_t) (err error) = SYS_LSTAT64
 //sys	Pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
 //sys	Pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
 //sys	sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) = SYS_SENDFILE64
@@ -74,7 +72,6 @@ func Pipe2(p []int, flags int) (err error) {
 //sysnb	Setresuid(ruid int, euid int, suid int) (err error) = SYS_SETRESUID32
 //sysnb	Setreuid(ruid int, euid int) (err error) = SYS_SETREUID32
 //sys	Splice(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error)
-//sys	Stat(path string, stat *Stat_t) (err error) = SYS_STAT64
 //sys	SyncFileRange(fd int, off int64, n int64, flags int) (err error)
 //sys	Truncate(path string, length int64) (err error) = SYS_TRUNCATE64
 //sysnb	getgroups(n int, list *_Gid_t) (nn int, err error) = SYS_GETGROUPS32
@@ -84,6 +81,18 @@ func Pipe2(p []int, flags int) (err error) {
 //sys	mmap2(addr uintptr, length uintptr, prot int, flags int, fd int, pageOffset uintptr) (xaddr uintptr, err error)
 //sys	EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error)
 
+func Stat(path string, stat *Stat_t) (err error) {
+	return fstatat(_AT_FDCWD, path, stat, 0)
+}
+
+func Lchown(path string, uid int, gid int) (err error) {
+	return Fchownat(_AT_FDCWD, path, uid, gid, _AT_SYMLINK_NOFOLLOW)
+}
+
+func Lstat(path string, stat *Stat_t) (err error) {
+	return fstatat(_AT_FDCWD, path, stat, _AT_SYMLINK_NOFOLLOW)
+}
+
 func mmap(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error) {
 	page := uintptr(offset / 4096)
 	if offset != int64(page)*4096 {

src/syscall/syscall_linux_amd64.go

@@ -22,9 +22,7 @@ const (
 //sysnb	InotifyInit() (fd int, err error)
 //sys	Ioperm(from int, num int, on int) (err error)
 //sys	Iopl(level int) (err error)
-//sys	Lchown(path string, uid int, gid int) (err error)
 //sys	Listen(s int, n int) (err error)
-//sys	Lstat(path string, stat *Stat_t) (err error)
 //sys	Pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
 //sys	Pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
 //sys	Seek(fd int, offset int64, whence int) (off int64, err error) = SYS_LSEEK
@@ -66,6 +64,14 @@ func Stat(path string, stat *Stat_t) (err error) {
 	return fstatat(_AT_FDCWD, path, stat, 0)
 }
 
+func Lchown(path string, uid int, gid int) (err error) {
+	return Fchownat(_AT_FDCWD, path, uid, gid, _AT_SYMLINK_NOFOLLOW)
+}
+
+func Lstat(path string, stat *Stat_t) (err error) {
+	return fstatat(_AT_FDCWD, path, stat, _AT_SYMLINK_NOFOLLOW)
+}
+
 //go:noescape
 func gettimeofday(tv *Timeval) (err Errno)
 

src/syscall/syscall_linux_arm.go

@@ -83,9 +83,7 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 //sysnb	Getgid() (gid int) = SYS_GETGID32
 //sysnb	Getuid() (uid int) = SYS_GETUID32
 //sysnb	InotifyInit() (fd int, err error)
-//sys	Lchown(path string, uid int, gid int) (err error) = SYS_LCHOWN32
 //sys	Listen(s int, n int) (err error)
-//sys	Lstat(path string, stat *Stat_t) (err error) = SYS_LSTAT64
 //sys	sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) = SYS_SENDFILE64
 //sys	Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *Timeval) (n int, err error) = SYS__NEWSELECT
 //sys	Setfsgid(gid int) (err error) = SYS_SETFSGID32
@@ -96,7 +94,6 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 //sysnb	Setreuid(ruid int, euid int) (err error) = SYS_SETREUID32
 //sys	Shutdown(fd int, how int) (err error)
 //sys	Splice(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error)
-//sys	Stat(path string, stat *Stat_t) (err error) = SYS_STAT64
 
 // Vsyscalls on amd64.
 //sysnb	Gettimeofday(tv *Timeval) (err error)
@@ -110,6 +107,18 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 //sys	mmap2(addr uintptr, length uintptr, prot int, flags int, fd int, pageOffset uintptr) (xaddr uintptr, err error)
 //sys	EpollWait(epfd int, events []EpollEvent, msec int) (n int, err error)
 
+func Stat(path string, stat *Stat_t) (err error) {
+	return fstatat(_AT_FDCWD, path, stat, 0)
+}
+
+func Lchown(path string, uid int, gid int) (err error) {
+	return Fchownat(_AT_FDCWD, path, uid, gid, _AT_SYMLINK_NOFOLLOW)
+}
+
+func Lstat(path string, stat *Stat_t) (err error) {
+	return fstatat(_AT_FDCWD, path, stat, _AT_SYMLINK_NOFOLLOW)
+}
+
 func Fstatfs(fd int, buf *Statfs_t) (err error) {
 	_, _, e := Syscall(SYS_FSTATFS64, uintptr(fd), unsafe.Sizeof(*buf), uintptr(unsafe.Pointer(buf)))
 	if e != 0 {