syscall: use the nsec system call instead of /dev/bintime on Plan 9

Also remove arch-specific Go files in the Plan 9 syscall package

LGTM=0intro
R=0intro, dave
CC=ality, golang-codereviews, jas, mischief, rsc
https://golang.org/cl/112720043

src/pkg/syscall/syscall_plan9.go

@@ -295,30 +295,25 @@ func NsecToTimeval(nsec int64) (tv Timeval) {
 	return
 }
 
-func DecodeBintime(b []byte) (nsec int64, err error) {
-	if len(b) != 8 {
-		return -1, NewError("bad /dev/bintime format")
+func nsec() int64 {
+	var scratch int64
+
+	r0, _, _ := Syscall(SYS_NSEC, uintptr(unsafe.Pointer(&scratch)), 0, 0)
+	// TODO(aram): remove hack after I fix _nsec in the pc64 kernel.
+	if r0 == 0 {
+		return scratch
 	}
-	nsec = int64(b[0])<<56 |
-		int64(b[1])<<48 |
-		int64(b[2])<<40 |
-		int64(b[3])<<32 |
-		int64(b[4])<<24 |
-		int64(b[5])<<16 |
-		int64(b[6])<<8 |
-		int64(b[7])
-	return
+	return int64(r0)
 }
 
 func Gettimeofday(tv *Timeval) error {
-	nsec, e := nanotime()
-	if e != nil {
-		return e
-	}
+	nsec := nsec()
 	*tv = NsecToTimeval(nsec)
-	return e
+	return nil
 }
 
+func Getpagesize() int { return 0x1000 }
+
 func Getegid() (egid int) { return -1 }
 func Geteuid() (euid int) { return -1 }
 func Getgid() (gid int)   { return -1 }

src/pkg/syscall/syscall_plan9_386.go

-// 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.
-
-package syscall
-
-func Getpagesize() int { return 0x1000 }
-
-func nanotime() (nsec int64, err error) {
-	// TODO(paulzhol):
-	// avoid reopening a file descriptor for /dev/bintime on each call,
-	// use lower-level calls to avoid allocation.
-
-	var b [8]byte
-	nsec = -1
-
-	fd, err := Open("/dev/bintime", O_RDONLY)
-	if err != nil {
-		return
-	}
-	defer Close(fd)
-
-	if _, err = Pread(fd, b[:], 0); err != nil {
-		return
-	}
-
-	if nsec, err = DecodeBintime(b[:]); err != nil {
-		return -1, err
-	}
-
-	return
-}

src/pkg/syscall/syscall_plan9_amd64.go

-// 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.
-
-package syscall
-
-func Getpagesize() int { return 0x200000 }
-
-// Used by Gettimeofday, which expects
-// an error return value.
-func nanotime() (int64, error) {
-	r1, _, _ := RawSyscall(SYS_NANOTIME, 0, 0, 0)
-	return int64(r1), nil
-}

src/pkg/syscall/zsysnum_plan9_386.go

@@ -44,4 +44,6 @@ const (
 	SYS_AWAIT       = 47
 	SYS_PREAD       = 50
 	SYS_PWRITE      = 51
+	SYS_TSEMACQUIRE = 52
+	SYS_NSEC        = 53
 )

src/pkg/syscall/zsysnum_plan9_amd64.go

@@ -44,5 +44,6 @@ const (
 	SYS_AWAIT       = 47
 	SYS_PREAD       = 50
 	SYS_PWRITE      = 51
-	SYS_NANOTIME   = 60
+	SYS_TSEMACQUIRE = 52
+	SYS_NSEC        = 53
 )