Use golang.org/x/sys/execabs

Signed-off-by: Tibor Vass <tibor@docker.com>

vendor/golang.org/x/sys/plan9/syscall.go

@@ -24,16 +24,20 @@
 // holds a value of type syscall.ErrorString.
 package plan9 // import "golang.org/x/sys/plan9"
 
-import "unsafe"
+import (
+	"bytes"
+	"strings"
+	"unsafe"
+
+	"golang.org/x/sys/internal/unsafeheader"
+)
 
 // ByteSliceFromString returns a NUL-terminated slice of bytes
 // containing the text of s. If s contains a NUL byte at any
 // location, it returns (nil, EINVAL).
 func ByteSliceFromString(s string) ([]byte, error) {
-	for i := 0; i < len(s); i++ {
-		if s[i] == 0 {
-			return nil, EINVAL
-		}
+	if strings.IndexByte(s, 0) != -1 {
+		return nil, EINVAL
 	}
 	a := make([]byte, len(s)+1)
 	copy(a, s)
@@ -51,6 +55,41 @@ func BytePtrFromString(s string) (*byte, error) {
 	return &a[0], nil
 }
 
+// ByteSliceToString returns a string form of the text represented by the slice s, with a terminating NUL and any
+// bytes after the NUL removed.
+func ByteSliceToString(s []byte) string {
+	if i := bytes.IndexByte(s, 0); i != -1 {
+		s = s[:i]
+	}
+	return string(s)
+}
+
+// BytePtrToString takes a pointer to a sequence of text and returns the corresponding string.
+// If the pointer is nil, it returns the empty string. It assumes that the text sequence is terminated
+// at a zero byte; if the zero byte is not present, the program may crash.
+func BytePtrToString(p *byte) string {
+	if p == nil {
+		return ""
+	}
+	if *p == 0 {
+		return ""
+	}
+
+	// Find NUL terminator.
+	n := 0
+	for ptr := unsafe.Pointer(p); *(*byte)(ptr) != 0; n++ {
+		ptr = unsafe.Pointer(uintptr(ptr) + 1)
+	}
+
+	var s []byte
+	h := (*unsafeheader.Slice)(unsafe.Pointer(&s))
+	h.Data = unsafe.Pointer(p)
+	h.Len = n
+	h.Cap = n
+
+	return string(s)
+}
+
 // Single-word zero for use when we need a valid pointer to 0 bytes.
 // See mksyscall.pl.
 var _zero uintptr