syscall: Reimplement linux syscalls in terms of their *at replacements.

Updates #9974

This proposal tackles the body of syscalls which have been replaced,
and are now deprecated in linux. This is needed for the arm64 port as
arm64 is the first linux architecture to remove the "legacy" forms of
these syscalls.

The *AT variants were added in kernel 2.6.16, so well before our 2.6.23
cutoff (hey, it'll even work on RHEL5).

Discussion: https://groups.google.com/forum/#!topic/golang-dev/zpeFtN2z5Fc

Change-Id: I473a7c9a295d6f776fcdc75dcce06cbe9e3564ee
Reviewed-on: https://go-review.googlesource.com/5837Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/syscall_linux.go

@@ -17,10 +17,38 @@ import "unsafe"
  * Wrapped
  */
 
-//sys	open(path string, mode int, perm uint32) (fd int, err error)
+func Access(path string, mode uint32) (err error) {
+	return Faccessat(_AT_FDCWD, path, mode, 0)
+}
+
+func Chmod(path string, mode uint32) (err error) {
+	return Fchmodat(_AT_FDCWD, path, mode, 0)
+}
+
+func Chown(path string, uid int, gid int) (err error) {
+	return Fchownat(_AT_FDCWD, path, uid, gid, 0)
+}
+
+func Creat(path string, mode uint32) (fd int, err error) {
+	return Open(path, O_CREAT|O_WRONLY|O_TRUNC, mode)
+}
+
+//sys	linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error)
+
+func Link(oldpath string, newpath string) (err error) {
+	return linkat(_AT_FDCWD, oldpath, _AT_FDCWD, newpath, 0)
+}
+
+func Mkdir(path string, mode uint32) (err error) {
+	return Mkdirat(_AT_FDCWD, path, mode)
+}
+
+func Mknod(path string, mode uint32, dev int) (err error) {
+	return Mknodat(_AT_FDCWD, path, mode, dev)
+}
 
 func Open(path string, mode int, perm uint32) (fd int, err error) {
-	return open(path, mode|O_LARGEFILE, perm)
+	return openat(_AT_FDCWD, path, mode|O_LARGEFILE, perm)
 }
 
 //sys	openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
@@ -29,6 +57,36 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 	return openat(dirfd, path, flags|O_LARGEFILE, mode)
 }
 
+//sys	readlinkat(dirfd int, path string, buf []byte) (n int, err error)
+
+func Readlink(path string, buf []byte) (n int, err error) {
+	return readlinkat(_AT_FDCWD, path, buf)
+}
+
+func Rename(oldpath string, newpath string) (err error) {
+	return Renameat(_AT_FDCWD, oldpath, _AT_FDCWD, newpath)
+}
+
+func Rmdir(path string) error {
+	return unlinkat(_AT_FDCWD, path, _AT_REMOVEDIR)
+}
+
+//sys	symlinkat(oldpath string, newdirfd int, newpath string) (err error)
+
+func Symlink(oldpath string, newpath string) (err error) {
+	return symlinkat(oldpath, _AT_FDCWD, newpath)
+}
+
+func Unlink(path string) error {
+	return unlinkat(_AT_FDCWD, path, 0)
+}
+
+//sys	unlinkat(dirfd int, path string, flags int) (err error)
+
+func Unlinkat(dirfd int, path string) error {
+	return unlinkat(dirfd, path, 0)
+}
+
 //sys	utimes(path string, times *[2]Timeval) (err error)
 
 func Utimes(path string, tv []Timeval) (err error) {
@@ -757,14 +815,11 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 /*
  * Direct access
  */
-//sys	Access(path string, mode uint32) (err error)
 //sys	Acct(path string) (err error)
 //sys	Adjtimex(buf *Timex) (state int, err error)
 //sys	Chdir(path string) (err error)
-//sys	Chmod(path string, mode uint32) (err error)
 //sys	Chroot(path string) (err error)
 //sys	Close(fd int) (err error)
-//sys	Creat(path string, mode uint32) (fd int, err error)
 //sysnb	Dup(oldfd int) (fd int, err error)
 //sysnb	Dup3(oldfd int, newfd int, flags int) (err error)
 //sysnb	EpollCreate(size int) (fd int, err error)
@@ -797,22 +852,16 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 //sysnb	InotifyRmWatch(fd int, watchdesc uint32) (success int, err error)
 //sysnb	Kill(pid int, sig Signal) (err error)
 //sys	Klogctl(typ int, buf []byte) (n int, err error) = SYS_SYSLOG
-//sys	Link(oldpath string, newpath string) (err error)
 //sys	Listxattr(path string, dest []byte) (sz int, err error)
-//sys	Mkdir(path string, mode uint32) (err error)
 //sys	Mkdirat(dirfd int, path string, mode uint32) (err error)
-//sys	Mknod(path string, mode uint32, dev int) (err error)
 //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
 //sys	Pause() (err error)
 //sys	PivotRoot(newroot string, putold string) (err error) = SYS_PIVOT_ROOT
 //sysnb prlimit(pid int, resource int, old *Rlimit, newlimit *Rlimit) (err error) = SYS_PRLIMIT64
 //sys	read(fd int, p []byte) (n int, err error)
-//sys	Readlink(path string, buf []byte) (n int, err error)
 //sys	Removexattr(path string, attr string) (err error)
-//sys	Rename(oldpath string, newpath string) (err error)
 //sys	Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error)
-//sys	Rmdir(path string) (err error)
 //sys	Setdomainname(p []byte) (err error)
 //sys	Sethostname(p []byte) (err error)
 //sysnb	Setpgid(pid int, pgid int) (err error)
@@ -834,7 +883,6 @@ func Setgid(uid int) (err error) {
 
 //sys	Setpriority(which int, who int, prio int) (err error)
 //sys	Setxattr(path string, attr string, data []byte, flags int) (err error)
-//sys	Symlink(oldpath string, newpath string) (err error)
 //sys	Sync()
 //sysnb	Sysinfo(info *Sysinfo_t) (err error)
 //sys	Tee(rfd int, wfd int, len int, flags int) (n int64, err error)
@@ -842,8 +890,6 @@ func Setgid(uid int) (err error) {
 //sysnb	Times(tms *Tms) (ticks uintptr, err error)
 //sysnb	Umask(mask int) (oldmask int)
 //sysnb	Uname(buf *Utsname) (err error)
-//sys	Unlink(path string) (err error)
-//sys	Unlinkat(dirfd int, path string) (err error)
 //sys	Unmount(target string, flags int) (err error) = SYS_UMOUNT2
 //sys	Unshare(flags int) (err error)
 //sys	Ustat(dev int, ubuf *Ustat_t) (err error)

src/syscall/syscall_linux_386.go

@@ -56,7 +56,6 @@ func Pipe2(p []int, flags int) (err error) {
 
 // 64-bit file system and 32-bit uid calls
 // (386 default is 32-bit file system and 16-bit uid).
-//sys	Chown(path string, uid int, gid int) (err error) = SYS_CHOWN32
 //sysnb	Dup2(oldfd int, newfd int) (err error)
 //sys	Fchown(fd int, uid int, gid int) (err error) = SYS_FCHOWN32
 //sys	Fstat(fd int, stat *Stat_t) (err error) = SYS_FSTAT64

src/syscall/syscall_linux_amd64.go

@@ -4,7 +4,6 @@
 
 package syscall
 
-//sys	Chown(path string, uid int, gid int) (err error)
 //sysnb	Dup2(oldfd int, newfd int) (err error)
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fstat(fd int, stat *Stat_t) (err error)

src/syscall/syscall_linux_arm.go

@@ -78,7 +78,6 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 
 // 64-bit file system and 32-bit uid calls
 // (16-bit uid calls are not always supported in newer kernels)
-//sys	Chown(path string, uid int, gid int) (err error) = SYS_CHOWN32
 //sysnb	Dup2(oldfd int, newfd int) (err error)
 //sys	Fchown(fd int, uid int, gid int) (err error) = SYS_FCHOWN32
 //sys	Fstat(fd int, stat *Stat_t) (err error) = SYS_FSTAT64

src/syscall/syscall_linux_ppc64x.go

@@ -7,7 +7,6 @@
 
 package syscall
 
-//sys	Chown(path string, uid int, gid int) (err error)
 //sysnb	Dup2(oldfd int, newfd int) (err error)
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fstat(fd int, stat *Stat_t) (err error)