cmd/dist: reactivate vfp detection on linux/arm

Fixes #9732
Fixes #9819

Rather than detecting vfp support via catching SIGILL signals,
parse the contents of /proc/cpuinfo.

As the GOARM values for NaCl and freebsd are hard coded, this parsing
logic only needs to support linux/arm.

This change also fixes the nacl/arm build which is broken because the
first stage of nacltest.bash is executed with GOARM=5, embedding that
into 5g.

The second stage of nacltest.bash correctly detects GOARM=7, but this is
ignored as we pass --no-clean at that point, and thus do not replace
the compiler.

Lastyly, include a fix to error message in nacltest.bash

Change-Id: I13f306ff07a99b44b493fade72ac00d0d5097e1c
Reviewed-on: https://go-review.googlesource.com/3981Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/dist/util.go

@@ -471,24 +471,38 @@ func xgetgoarm() string {
 		// FreeBSD has broken VFP support.
 		return "5"
 	}
-	if xtryexecfunc(useVFPv3) {
+	if goos != "linux" {
+		// All other arm platforms that we support
+		// require ARMv7.
 		return "7"
 	}
-	if xtryexecfunc(useVFPv1) {
-		return "6"
+	cpuinfo := readfile("/proc/cpuinfo")
+	goarm := "5"
+	for _, line := range splitlines(cpuinfo) {
+		line := strings.SplitN(line, ":", 2)
+		if len(line) < 2 {
+			continue
+		}
+		if strings.TrimSpace(line[0]) != "Features" {
+			continue
+		}
+		features := splitfields(line[1])
+		sort.Strings(features) // so vfpv3 sorts after vfp
+
+		// Infer GOARM value from the vfp features available
+		// on this host. Values of GOARM detected are:
+		// 5: no vfp support was found
+		// 6: vfp (v1) support was detected, but no higher
+		// 7: vfpv3 support was detected.
+		// This matches the assertions in runtime.checkarm.
+		for _, f := range features {
+			switch f {
+			case "vfp":
+				goarm = "6"
+			case "vfpv3":
+				goarm = "7"
+			}
+		}
 	}
-	return "5"
+	return goarm
 }
-
-func xtryexecfunc(f func()) bool {
-	// TODO(rsc): Implement.
-	// The C cmd/dist used this to test whether certain assembly
-	// sequences could be executed properly. It used signals and
-	// timers and sigsetjmp, which is basically not possible in Go.
-	// We probably have to invoke ourselves as a subprocess instead,
-	// to contain the fault/timeout.
-	return false
-}
-
-func useVFPv1()
-func useVFPv3()

src/cmd/dist/vfp_arm.s

-// Copyright 2015 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.
-
-#include "textflag.h"
-
-// try to run "vmov.f64 d0, d0" instruction
-TEXT ·useVFPv1(SB),NOSPLIT,$0
-	WORD $0xeeb00b40	// vmov.f64 d0, d0
-	RET
-
-// try to run VFPv3-only "vmov.f64 d0, #112" instruction
-TEXT ·useVFPv3(SB),NOSPLIT,$0
-	WORD $0xeeb70b00	// vmov.f64 d0, #112
-	RET

src/cmd/dist/vfp_default.s

-// Copyright 2015 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 !arm
-
-#include "textflag.h"
-
-TEXT ·useVFPv1(SB),NOSPLIT,$0
-	RET
-
-TEXT ·useVFPv3(SB),NOSPLIT,$0
-	RET
-

src/nacltest.bash

@@ -62,7 +62,7 @@ fi
 # Run host build to get toolchain for running zip generator.
 unset GOOS GOARCH
 if [ ! -f make.bash ]; then
-	echo 'nacl.bash must be run from $GOROOT/src' 1>&2
+	echo 'nacltest.bash must be run from $GOROOT/src' 1>&2
 	exit 1
 fi
 GOOS=$GOHOSTOS GOARCH=$GOHOSTARCH ./make.bash