unix: don't use syscall.ParseDirent

Implement ParseDirent in x/sys/unix instead of calling
syscall.ParseDirent. The latter uses offsets into syscall.Dirent which
might not be matching unix.Dirent depending on Go version. This is e.g.
the case with of FreeBSD whose Dirent structure was updated for Go 1.12.

This fixes TestDirent and TestGetdirentries on freebsd with Go 1.11

Reverts CL 88475

Change-Id: I04318f59c6fbf148c75ce3667255a0c0428288e2
Reviewed-on: https://go-review.googlesource.com/c/sys/+/183897
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>

unix/dirent.go

@@ -6,12 +6,97 @@
 
 package unix
 
-import "syscall"
+import "unsafe"
+
+// readInt returns the size-bytes unsigned integer in native byte order at offset off.
+func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {
+	if len(b) < int(off+size) {
+		return 0, false
+	}
+	if isBigEndian {
+		return readIntBE(b[off:], size), true
+	}
+	return readIntLE(b[off:], size), true
+}
+
+func readIntBE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[1]) | uint64(b[0])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[3]) | uint64(b[2])<<8 | uint64(b[1])<<16 | uint64(b[0])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
+			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
+}
+
+func readIntLE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
+}
 
 // ParseDirent parses up to max directory entries in buf,
 // appending the names to names. It returns the number of
 // bytes consumed from buf, the number of entries added
 // to names, and the new names slice.
 func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	return syscall.ParseDirent(buf, max, names)
+	origlen := len(buf)
+	count = 0
+	for max != 0 && len(buf) > 0 {
+		reclen, ok := direntReclen(buf)
+		if !ok || reclen > uint64(len(buf)) {
+			return origlen, count, names
+		}
+		rec := buf[:reclen]
+		buf = buf[reclen:]
+		ino, ok := direntIno(rec)
+		if !ok {
+			break
+		}
+		if ino == 0 { // File absent in directory.
+			continue
+		}
+		const namoff = uint64(unsafe.Offsetof(Dirent{}.Name))
+		namlen, ok := direntNamlen(rec)
+		if !ok || namoff+namlen > uint64(len(rec)) {
+			break
+		}
+		name := rec[namoff : namoff+namlen]
+		for i, c := range name {
+			if c == 0 {
+				name = name[:i]
+				break
+			}
+		}
+		// Check for useless names before allocating a string.
+		if string(name) == "." || string(name) == ".." {
+			continue
+		}
+		max--
+		count++
+		names = append(names, string(name))
+	}
+	return origlen - len(buf), count, names
 }

unix/syscall_darwin.go

@@ -77,6 +77,18 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
+}
+
 //sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
 func PtraceAttach(pid int) (err error) { return ptrace(PT_ATTACH, pid, 0, 0) }
 func PtraceDetach(pid int) (err error) { return ptrace(PT_DETACH, pid, 0, 0) }

unix/syscall_dragonfly.go

@@ -57,6 +57,22 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	namlen, ok := direntNamlen(buf)
+	if !ok {
+		return 0, false
+	}
+	return (16 + namlen + 1 + 7) &^ 7, true
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
+}
+
 //sysnb pipe() (r int, w int, err error)
 
 func Pipe(p []int) (err error) {

unix/syscall_freebsd.go

@@ -82,6 +82,18 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
+}
+
 func Pipe(p []int) (err error) {
 	return Pipe2(p, 0)
 }

unix/syscall_linux.go

@@ -1413,6 +1413,22 @@ func Reboot(cmd int) (err error) {
 	return reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd, "")
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
+	}
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
+}
+
 //sys	mount(source string, target string, fstype string, flags uintptr, data *byte) (err error)
 
 func Mount(source string, target string, fstype string, flags uintptr, data string) (err error) {

unix/syscall_netbsd.go

@@ -94,6 +94,18 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return mib, nil
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
+}
+
 func SysctlClockinfo(name string) (*Clockinfo, error) {
 	mib, err := sysctlmib(name)
 	if err != nil {

unix/syscall_openbsd.go

@@ -43,6 +43,18 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return nil, EINVAL
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
+}
+
 func SysctlClockinfo(name string) (*Clockinfo, error) {
 	mib, err := sysctlmib(name)
 	if err != nil {

unix/syscall_solaris.go

@@ -35,6 +35,22 @@ type SockaddrDatalink struct {
 	raw    RawSockaddrDatalink
 }
 
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
+	}
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
+}
+
 //sysnb	pipe(p *[2]_C_int) (n int, err error)
 
 func Pipe(p []int) (err error) {