syscall: check Fchmodat flags parameter on Linux

As mentioned in #25845, port CL 46474 from golang.org/x/sys/unix to the
syscall package.

Currently Linux' fchmodat(2) syscall implementation doesn't support the
flags parameter (though it might in future versions [1]). Fchmodat in
the syscall package takes the parameter and (wrongly) passes it on to the
syscall which will ignore it.

According to the POSIX.1-2008 manual page [2], AT_SYMLINK_NOFOLLOW is
the only valid value for the flags parameter and EOPNOTSUPP should be
returned in case changing the mode of a symbolic link is not supported
by the underlying system. EINVAL should be returned for any other value
of the flags parameter.

  [1] https://patchwork.kernel.org/patch/9596301/
  [2] http://pubs.opengroup.org/onlinepubs/9699919799/functions/chmod.html

Updates #20130
Updates #25845

Change-Id: I1021dd0e6a4f4cb3557cb1c1b34dd618c378cda6
Reviewed-on: https://go-review.googlesource.com/118658
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 15 insertions, 15 deletions

diff --git a/src/syscall/zsyscall_linux_mipsle.go b/src/syscall/zsyscall_linux_mipsle.go
index c3e8d92035..0b2862d1cb 100644
--- a/src/syscall/zsyscall_linux_mipsle.go
+++ b/src/syscall/zsyscall_linux_mipsle.go
@@ -9,6 +9,21 @@ import "unsafe"
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func fchmodat(dirfd int, path string, mode uint32) (err error) {
+	var _p0 *byte
+	_p0, err = BytePtrFromString(path)
+	if err != nil {
+		return
+	}
+	_, _, e1 := Syscall(SYS_FCHMODAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(mode))
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error) {
 	var _p0 *byte
 	_p0, err = BytePtrFromString(oldpath)
@@ -384,21 +399,6 @@ func Fchmod(fd int, mode uint32) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
-	var _p0 *byte
-	_p0, err = BytePtrFromString(path)
-	if err != nil {
-		return
-	}
-	_, _, e1 := Syscall6(SYS_FCHMODAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(mode), uintptr(flags), 0, 0)
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
 	var _p0 *byte
 	_p0, err = BytePtrFromString(path)