types/pad32: delete package

Use Go 1.19's new 64-bit alignment ~hidden feature instead.

Fixes #5356

Change-Id: Ifcbcb115875a7da01df3bc29e9e7feadce5bc956
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/depaware.txt

@@ -64,7 +64,6 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         tailscale.com/types/logger                                   from tailscale.com/cmd/derper+
         tailscale.com/types/netmap                                   from tailscale.com/ipn
         tailscale.com/types/opt                                      from tailscale.com/client/tailscale+
-        tailscale.com/types/pad32                                    from tailscale.com/derp
         tailscale.com/types/persist                                  from tailscale.com/ipn
         tailscale.com/types/preftype                                 from tailscale.com/ipn
         tailscale.com/types/structs                                  from tailscale.com/ipn+

cmd/tailscale/depaware.txt

@@ -87,7 +87,6 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/types/netmap                                   from tailscale.com/ipn
         tailscale.com/types/nettype                                  from tailscale.com/net/netcheck+
         tailscale.com/types/opt                                      from tailscale.com/net/netcheck+
-        tailscale.com/types/pad32                                    from tailscale.com/derp
         tailscale.com/types/persist                                  from tailscale.com/ipn
         tailscale.com/types/preftype                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/types/structs                                  from tailscale.com/ipn+

cmd/tailscaled/depaware.txt

@@ -266,7 +266,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/wgengine/magicsock+
         tailscale.com/types/opt                                      from tailscale.com/control/controlclient+
-        tailscale.com/types/pad32                                    from tailscale.com/derp
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+

derp/derp_server.go

@@ -42,7 +42,6 @@ import (
 	"tailscale.com/metrics"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
-	"tailscale.com/types/pad32"
 	"tailscale.com/version"
 )
 
@@ -89,6 +88,8 @@ const (
 	disableFighters
 )
 
+type align64 [0]atomic.Int64 // for side effect of its 64-bit alignment
+
 // Server is a DERP server.
 type Server struct {
 	// WriteTimeout, if non-zero, specifies how long to wait
@@ -111,14 +112,14 @@ type Server struct {
 	packetsRecvByKind            metrics.LabelMap
 	packetsRecvDisco             *expvar.Int
 	packetsRecvOther             *expvar.Int
-	_                            pad32.Four
+	_                            align64
 	packetsDropped               expvar.Int
 	packetsDroppedReason         metrics.LabelMap
 	packetsDroppedReasonCounters []*expvar.Int // indexed by dropReason
 	packetsDroppedType           metrics.LabelMap
 	packetsDroppedTypeDisco      *expvar.Int
 	packetsDroppedTypeOther      *expvar.Int
-	_                            pad32.Four
+	_                            align64
 	packetsForwardedOut          expvar.Int
 	packetsForwardedIn           expvar.Int
 	peerGoneFrames               expvar.Int // number of peer gone frames sent

net/tstun/wrap.go

@@ -82,7 +82,7 @@ type Wrapper struct {
 
 	// lastActivityAtomic is read/written atomically.
 	// On 32 bit systems, if the fields above change,
-	// you might need to add a pad32.Four field here.
+	// you might need to add an align64 field here.
 	lastActivityAtomic mono.Time // time of last send or receive
 
 	destIPActivity syncs.AtomicValue[map[netip.Addr]func()]

types/pad32/pad32.go

@@ -1,9 +0,0 @@
-// Copyright (c) 2021 Tailscale Inc & 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 pad32 defines padding types that have width on only 32-bit platforms.
-package pad32
-
-// Four is 4 bytes of padding on 32-bit machines, else 0 bytes.
-type Four [4 * (1 - ((^uint(0))>>32)&1)]byte