unix: fix errors in syscalls when using -linkshared on ppc64x

When using -linkshared, the external linker on ppc64x cannot
always handle the direct branch to syscall.Syscall and similar
similar functions when the offset is too far. Instead it should
be done as a BL which can then be called through a procedure
linkage table entry.

This change removes functions Syscall, Syscall6,
RawSyscall, RawSyscall6 from asm_linux_ppc64x.s and instead
creates Go functions which call their corresponding
functions in the syscall package. As Go functions, they can be
inlined with the help of CL 147361.

Fixes golang/go#16662

Change-Id: Ibd2b6ec15b0781c3d7db25e249a3ffc9e1c2884b
Reviewed-on: https://go-review.googlesource.com/c/146518
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/asm_linux_ppc64x.s

@@ -15,12 +15,6 @@
 // Just jump to package syscall's implementation for all these functions.
 // The runtime may know about them.
 
-TEXT ·Syscall(SB),NOSPLIT,$0-56
-	BR	syscall·Syscall(SB)
-
-TEXT ·Syscall6(SB),NOSPLIT,$0-80
-	BR	syscall·Syscall6(SB)
-
 TEXT ·SyscallNoError(SB),NOSPLIT,$0-48
 	BL	runtime·entersyscall(SB)
 	MOVD	a1+8(FP), R3
@@ -36,12 +30,6 @@ TEXT ·SyscallNoError(SB),NOSPLIT,$0-48
 	BL	runtime·exitsyscall(SB)
 	RET
 
-TEXT ·RawSyscall(SB),NOSPLIT,$0-56
-	BR	syscall·RawSyscall(SB)
-
-TEXT ·RawSyscall6(SB),NOSPLIT,$0-80
-	BR	syscall·RawSyscall6(SB)
-
 TEXT ·RawSyscallNoError(SB),NOSPLIT,$0-48
 	MOVD	a1+8(FP), R3
 	MOVD	a2+16(FP), R4

unix/syscall_unix_gc.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build darwin dragonfly freebsd linux netbsd openbsd solaris
-// +build !gccgo
+// +build !gccgo,!ppc64le,!ppc64
 
 package unix
 

unix/syscall_unix_gc_ppc64x.go

@@ -0,0 +1,24 @@
+// Copyright 2018 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 linux
+// +build ppc64le ppc64
+// +build !gccgo
+
+package unix
+
+import "syscall"
+
+func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	return syscall.Syscall(trap, a1, a2, a3)
+}
+func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	return syscall.Syscall6(trap, a1, a2, a3, a4, a5, a6)
+}
+func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	return syscall.RawSyscall(trap, a1, a2, a3)
+}
+func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno) {
+	return syscall.RawSyscall6(trap, a1, a2, a3, a4, a5, a6)
+}