syscall: split implementation of Dup2 per linux GOOS

Updates #9974

This proposal moves the definition of Dup2 from the generic syscall_linux.go
to the GOOS specific variants. This is in preparation for the arm64 port.

For all existing platforms Dup2 is not affected. When arm64 is added we'll use
either a forwarding method to Dup3 or

	//sysnb        Dup2(oldfd int, newfd int) (err error) = SYS_DUP3

Because mksycall.pl does not sort symbols before generating the output file
the diff includes some unavoidable code moves as Dup2 is processed latter in
the run.

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

Change-Id: Icdedf55bb29e749c4230e1ee371bf9d0bd0cfb38
Reviewed-on: https://go-review.googlesource.com/5835Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>

src/syscall/syscall_linux.go

@@ -766,7 +766,6 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
 //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	Dup2(oldfd int, newfd int) (err error)
 //sysnb	Dup3(oldfd int, newfd int, flags int) (err error)
 //sysnb	EpollCreate(size int) (fd int, err error)
 //sysnb	EpollCreate1(flag int) (fd int, err error)

src/syscall/syscall_linux_386.go

@@ -57,6 +57,7 @@ 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
 //sys	Ftruncate(fd int, length int64) (err error) = SYS_FTRUNCATE64

src/syscall/syscall_linux_amd64.go

@@ -5,6 +5,7 @@
 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)
 //sys	Fstatfs(fd int, buf *Statfs_t) (err error)

src/syscall/syscall_linux_arm.go

@@ -79,6 +79,7 @@ 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
 //sysnb	Getegid() (egid int) = SYS_GETEGID32

src/syscall/syscall_linux_ppc64x.go

@@ -8,6 +8,7 @@
 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)
 //sys	Fstatfs(fd int, buf *Statfs_t) (err error)

src/syscall/zsyscall_linux_386.go

@@ -294,16 +294,6 @@ func Dup(oldfd int) (fd int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Dup2(oldfd int, newfd int) (err error) {
-	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
-	if e1 != 0 {
-		err = e1
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Dup3(oldfd int, newfd int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_DUP3, uintptr(oldfd), uintptr(newfd), uintptr(flags))
 	if e1 != 0 {
@@ -1412,6 +1402,16 @@ func Chown(path string, uid int, gid int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchown(fd int, uid int, gid int) (err error) {
 	_, _, e1 := Syscall(SYS_FCHOWN32, uintptr(fd), uintptr(uid), uintptr(gid))
 	if e1 != 0 {

src/syscall/zsyscall_linux_amd64.go

@@ -294,16 +294,6 @@ func Dup(oldfd int) (fd int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Dup2(oldfd int, newfd int) (err error) {
-	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
-	if e1 != 0 {
-		err = e1
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Dup3(oldfd int, newfd int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_DUP3, uintptr(oldfd), uintptr(newfd), uintptr(flags))
 	if e1 != 0 {
@@ -1392,6 +1382,16 @@ func Chown(path string, uid int, gid int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchown(fd int, uid int, gid int) (err error) {
 	_, _, e1 := Syscall(SYS_FCHOWN, uintptr(fd), uintptr(uid), uintptr(gid))
 	if e1 != 0 {

src/syscall/zsyscall_linux_arm.go

@@ -294,16 +294,6 @@ func Dup(oldfd int) (fd int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Dup2(oldfd int, newfd int) (err error) {
-	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
-	if e1 != 0 {
-		err = e1
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Dup3(oldfd int, newfd int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_DUP3, uintptr(oldfd), uintptr(newfd), uintptr(flags))
 	if e1 != 0 {
@@ -1581,6 +1571,16 @@ func Chown(path string, uid int, gid int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchown(fd int, uid int, gid int) (err error) {
 	_, _, e1 := Syscall(SYS_FCHOWN32, uintptr(fd), uintptr(uid), uintptr(gid))
 	if e1 != 0 {

src/syscall/zsyscall_linux_ppc64.go

@@ -294,16 +294,6 @@ func Dup(oldfd int) (fd int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Dup2(oldfd int, newfd int) (err error) {
-	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
-	if e1 != 0 {
-		err = e1
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Dup3(oldfd int, newfd int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_DUP3, uintptr(oldfd), uintptr(newfd), uintptr(flags))
 	if e1 != 0 {
@@ -1392,6 +1382,16 @@ func Chown(path string, uid int, gid int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchown(fd int, uid int, gid int) (err error) {
 	_, _, e1 := Syscall(SYS_FCHOWN, uintptr(fd), uintptr(uid), uintptr(gid))
 	if e1 != 0 {

src/syscall/zsyscall_linux_ppc64le.go

@@ -294,16 +294,6 @@ func Dup(oldfd int) (fd int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Dup2(oldfd int, newfd int) (err error) {
-	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
-	if e1 != 0 {
-		err = e1
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Dup3(oldfd int, newfd int, flags int) (err error) {
 	_, _, e1 := RawSyscall(SYS_DUP3, uintptr(oldfd), uintptr(newfd), uintptr(flags))
 	if e1 != 0 {
@@ -1392,6 +1382,16 @@ func Chown(path string, uid int, gid int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func Dup2(oldfd int, newfd int) (err error) {
+	_, _, e1 := RawSyscall(SYS_DUP2, uintptr(oldfd), uintptr(newfd), 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchown(fd int, uid int, gid int) (err error) {
 	_, _, e1 := Syscall(SYS_FCHOWN, uintptr(fd), uintptr(uid), uintptr(gid))
 	if e1 != 0 {