runtime: use runtime.sysargs to parse auxv on linux/arm

Make auxv parsing in linux/arm less of a special case.

* rename setup_auxv to sysargs
* exclude linux/arm from vdso_none.go
* move runtime.checkarm after runtime.sysargs so arm specific
  values are properly initialised

Change-Id: I1ca7f5844ad5a162337ff061a83933fc9a2b5ff6
Reviewed-on: https://go-review.googlesource.com/2681Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/asm_arm.s

@@ -59,7 +59,6 @@ nocgo:
 	MOVW	R0, g_stackguard0(g)
 	MOVW	R0, g_stackguard1(g)
 
-	BL	runtime·checkgoarm(SB)
 	BL	runtime·check(SB)
 
 	// saved argc, argv
@@ -68,6 +67,7 @@ nocgo:
 	MOVW	64(R13), R1
 	MOVW	R1, 8(R13)
 	BL	runtime·args(SB)
+	BL	runtime·checkgoarm(SB)
 	BL	runtime·osinit(SB)
 	BL	runtime·schedinit(SB)
 

src/runtime/os_linux_arm.go

@@ -34,8 +34,7 @@ func checkgoarm() {
 	}
 }
 
-//go:nosplit
-func setup_auxv(argc int32, argv **byte) {
+func sysargs(argc int32, argv **byte) {
 	// skip over argv, envv to get to auxv
 	n := argc + 1
 	for argv_index(argv, n) != nil {

src/runtime/rt0_linux_arm.s

@@ -53,9 +53,6 @@ TEXT _rt0_arm_linux1(SB),NOSPLIT,$-4
 	// SWI	$0 // restore signal handler
 	// ADD	$32, R13
 
-	SUB	$4, R13 // fake a stack frame for runtime·setup_auxv
-	BL	runtime·setup_auxv(SB)
-	ADD	$4, R13
 	B	runtime·rt0_go(SB)
 
 TEXT bad_abi<>(SB),NOSPLIT,$-4

src/runtime/vdso_none.go

@@ -4,6 +4,7 @@
 
 // +build !linux !amd64
 // +build !linux !386
+// +build !linux !arm
 
 package runtime