go.net/ipv6: simplify syscall shims

This CL replaces syscall duplicates with tiny syscall shims to help
to add new platform support, to improve existing platform support.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/166910043

ipv6/syscall_linux_386.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This code is a duplicate of syscall/syscall_linux_386.go with small
-// modifications.
-
 package ipv6
 
 import (
@@ -12,30 +9,22 @@ import (
 	"unsafe"
 )
 
-// On x86 Linux, all the socket calls go through an extra indirection,
-// I think because the 5-register system call interface can't handle
-// the 6-argument calls like sendto and recvfrom. Instead the
-// arguments to the underlying system call are the number below and a
-// pointer to an array of uintptr. We hide the pointer in the
-// socketcall assembly to avoid allocation on every system call.
-
 const (
-	// See /usr/include/linux/net.h.
-	_SETSOCKOPT = 14
-	_GETSOCKOPT = 15
+	sysGETSOCKOPT = 0xf
+	sysSETSOCKOPT = 0xe
 )
 
-var socketcall func(call int, a0, a1, a2, a3, a4, a5 uintptr) (int, syscall.Errno)
+func socketcall(call int, a0, a1, a2, a3, a4, a5 uintptr) (int, syscall.Errno)
 
-func getsockopt(fd int, level int, name int, v unsafe.Pointer, l *sysSockoptLen) error {
-	if _, errno := socketcall(_GETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(unsafe.Pointer(l)), 0); errno != 0 {
+func getsockopt(fd, level, name int, v unsafe.Pointer, l *sysSockoptLen) error {
+	if _, errno := socketcall(sysGETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(unsafe.Pointer(l)), 0); errno != 0 {
 		return error(errno)
 	}
 	return nil
 }
 
-func setsockopt(fd int, level int, name int, v unsafe.Pointer, l uintptr) error {
-	if _, errno := socketcall(_SETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(l), 0); errno != 0 {
+func setsockopt(fd, level, name int, v unsafe.Pointer, l sysSockoptLen) error {
+	if _, errno := socketcall(sysSETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(l), 0); errno != 0 {
 		return error(errno)
 	}
 	return nil

ipv6/syscall_linux_386.s

-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// This code is a duplicate of syscall/syscall_linux_386.s with small
-// modifications.
-
-#define SYS_SOCKETCALL	102	// from zsysnum_linux_386.go
-
-// func socketcallnosplit7(call int, a0, a1, a2, a3, a4, a5 uintptr) (n int, errno int)
-// Kernel interface gets call sub-number and pointer to a0 for Go 1.1.
-TEXT ·socketcallnosplit7(SB),7,$0
-	CALL	runtime·entersyscall(SB)
-	MOVL	$SYS_SOCKETCALL, AX	// syscall entry
-	MOVL	4(SP), BX		// socket call number
-	LEAL	8(SP), CX		// pointer to call arguments
-	MOVL	$0, DX
-	MOVL	$0, SI
-	MOVL	$0, DI
-	CALL	*runtime·_vdso(SB)
-	CMPL	AX, $0xfffff001
-	JLS	ok1
-	MOVL	$-1, 32(SP)		// n
-	NEGL	AX
-	MOVL	AX, 36(SP)		// errno
-	CALL	runtime·exitsyscall(SB)
-	RET
-ok1:
-	MOVL	AX, 32(SP)		// n
-	MOVL	$0, 36(SP)		// errno
-	CALL	runtime·exitsyscall(SB)
-	RET
-
-// func socketcallnosplit4(call int, a0, a1, a2, a3, a4, a5 uintptr) (n int, errno int)
-// Kernel interface gets call sub-number and pointer to a0 for Go 1.2.
-TEXT ·socketcallnosplit4(SB),4,$0-40
-	CALL	runtime·entersyscall(SB)
-	MOVL	$SYS_SOCKETCALL, AX	// syscall entry
-	MOVL	4(SP), BX		// socket call number
-	LEAL	8(SP), CX		// pointer to call arguments
-	MOVL	$0, DX
-	MOVL	$0, SI
-	MOVL	$0, DI
-	CALL	*runtime·_vdso(SB)
-	CMPL	AX, $0xfffff001
-	JLS	ok2
-	MOVL	$-1, 32(SP)		// n
-	NEGL	AX
-	MOVL	AX, 36(SP)		// errno
-	CALL	runtime·exitsyscall(SB)
-	RET
-ok2:
-	MOVL	AX, 32(SP)		// n
-	MOVL	$0, 36(SP)		// errno
-	CALL	runtime·exitsyscall(SB)
-	RET

ipv6/syscall_nosplit7_linux_386.go

-// Copyright 2013 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build go1.1,!go1.2
-
-package ipv6
-
-import "syscall"
-
-func socketcallnosplit7(call int, a0, a1, a2, a3, a4, a5 uintptr) (int, syscall.Errno)
-
-func init() {
-	socketcall = socketcallnosplit7
-}

ipv6/syscall_unix.go

@@ -11,14 +11,14 @@ import (
 	"unsafe"
 )
 
-func getsockopt(fd int, level, name int, v unsafe.Pointer, l *sysSockoptLen) error {
+func getsockopt(fd, level, name int, v unsafe.Pointer, l *sysSockoptLen) error {
 	if _, _, errno := syscall.Syscall6(syscall.SYS_GETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(unsafe.Pointer(l)), 0); errno != 0 {
 		return error(errno)
 	}
 	return nil
 }
 
-func setsockopt(fd int, level int, name int, v unsafe.Pointer, l uintptr) error {
+func setsockopt(fd, level, name int, v unsafe.Pointer, l sysSockoptLen) error {
 	if _, _, errno := syscall.Syscall6(syscall.SYS_SETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(v), uintptr(l), 0); errno != 0 {
 		return error(errno)
 	}

ipv6/syscall_nosplit4_linux_386.go → ipv6/thunk_linux_386.s

-// Copyright 2013 The Go Authors.  All rights reserved.
+// Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // +build go1.2
 
-package ipv6
-
-import "syscall"
-
-func socketcallnosplit4(call int, a0, a1, a2, a3, a4, a5 uintptr) (int, syscall.Errno)
-
-func init() {
-	socketcall = socketcallnosplit4
-}
+TEXT	·socketcall(SB),4,$0-36
+	JMP	syscall·socketcall(SB)