Make netstack (//pkg/tcpip) buildable for 32 bit

Doing so involved breaking dependencies between //pkg/tcpip and the rest
of gVisor, which are discouraged anyways.

Tested on the Go branch via:
  gvisor.dev/gvisor/pkg/tcpip/...

Addresses #1446.

PiperOrigin-RevId: 363081778

4 files changed, 27 insertions, 30 deletions

diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index e17e2085c..2bb1be5d6 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -492,7 +492,7 @@ func (e *endpoint) sendBatch(batchFD int, batch []*stack.PacketBuffer) (int, tcp
 
 		var mmsgHdr rawfile.MMsgHdr
 		mmsgHdr.Msg.Iov = &iovecs[0]
-		mmsgHdr.Msg.Iovlen = uint64(len(iovecs))
+		mmsgHdr.Msg.SetIovlen((len(iovecs)))
 		mmsgHdrs = append(mmsgHdrs, mmsgHdr)
 	}
 
diff --git a/pkg/tcpip/link/fdbased/packet_dispatchers.go b/pkg/tcpip/link/fdbased/packet_dispatchers.go
index 46df87f44..a7adf822b 100644
--- a/pkg/tcpip/link/fdbased/packet_dispatchers.go
+++ b/pkg/tcpip/link/fdbased/packet_dispatchers.go
@@ -68,10 +68,8 @@ func (b *iovecBuffer) nextIovecs() []unix.Iovec {
 		// The kernel adds virtioNetHdr before each packet, but
 		// we don't use it, so so we allocate a buffer for it,
 		// add it in iovecs but don't add it in a view.
-		b.iovecs[0] = unix.Iovec{
-			Base: &vnetHdr[0],
-			Len:  uint64(virtioNetHdrSize),
-		}
+		b.iovecs[0] = unix.Iovec{Base: &vnetHdr[0]}
+		b.iovecs[0].SetLen(virtioNetHdrSize)
 		vnetHdrOff++
 	}
 	for i := range b.views {
@@ -80,10 +78,8 @@ func (b *iovecBuffer) nextIovecs() []unix.Iovec {
 		}
 		v := buffer.NewView(b.sizes[i])
 		b.views[i] = v
-		b.iovecs[i+vnetHdrOff] = unix.Iovec{
-			Base: &v[0],
-			Len:  uint64(len(v)),
-		}
+		b.iovecs[i+vnetHdrOff] = unix.Iovec{Base: &v[0]}
+		b.iovecs[i+vnetHdrOff].SetLen(len(v))
 	}
 	return b.iovecs
 }
@@ -235,7 +231,7 @@ func (d *recvMMsgDispatcher) dispatch() (bool, tcpip.Error) {
 		iovLen := len(iovecs)
 		d.msgHdrs[k].Len = 0
 		d.msgHdrs[k].Msg.Iov = &iovecs[0]
-		d.msgHdrs[k].Msg.Iovlen = uint64(iovLen)
+		d.msgHdrs[k].Msg.SetIovlen(iovLen)
 	}
 
 	nMsgs, err := rawfile.BlockingRecvMMsg(d.fd, d.msgHdrs)
diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index c1678c4f4..80fb343c5 100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
@@ -17,7 +17,6 @@ package tun
 import (
 	"fmt"
 
-	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -49,7 +48,14 @@ type Device struct {
 	mu           sync.RWMutex `state:"nosave"`
 	endpoint     *tunEndpoint
 	notifyHandle *channel.NotificationHandle
-	flags        uint16
+	flags        Flags
+}
+
+// Flags set properties of a Device
+type Flags struct {
+	TUN          bool
+	TAP          bool
+	NoPacketInfo bool
 }
 
 // beforeSave is invoked by stateify.
@@ -77,7 +83,7 @@ func (d *Device) Release(ctx context.Context) {
 }
 
 // SetIff services TUNSETIFF ioctl(2) request.
-func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
+func (d *Device) SetIff(s *stack.Stack, name string, flags Flags) error {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
@@ -85,21 +91,18 @@ func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
 		return syserror.EINVAL
 	}
 
-	// Input validations.
-	isTun := flags&linux.IFF_TUN != 0
-	isTap := flags&linux.IFF_TAP != 0
-	supportedFlags := uint16(linux.IFF_TUN | linux.IFF_TAP | linux.IFF_NO_PI)
-	if isTap && isTun || !isTap && !isTun || flags&^supportedFlags != 0 {
+	// Input validation.
+	if flags.TAP && flags.TUN || !flags.TAP && !flags.TUN {
 		return syserror.EINVAL
 	}
 
 	prefix := "tun"
-	if isTap {
+	if flags.TAP {
 		prefix = "tap"
 	}
 
 	linkCaps := stack.CapabilityNone
-	if isTap {
+	if flags.TAP {
 		linkCaps |= stack.CapabilityResolutionRequired
 	}
 
@@ -177,7 +180,7 @@ func (d *Device) Write(data []byte) (int64, error) {
 
 	// Packet information.
 	var pktInfoHdr PacketInfoHeader
-	if !d.hasFlags(linux.IFF_NO_PI) {
+	if !d.flags.NoPacketInfo {
 		if len(data) < PacketInfoHeaderSize {
 			// Ignore bad packet.
 			return dataLen, nil
@@ -188,7 +191,7 @@ func (d *Device) Write(data []byte) (int64, error) {
 
 	// Ethernet header (TAP only).
 	var ethHdr header.Ethernet
-	if d.hasFlags(linux.IFF_TAP) {
+	if d.flags.TAP {
 		if len(data) < header.EthernetMinimumSize {
 			// Ignore bad packet.
 			return dataLen, nil
@@ -253,7 +256,7 @@ func (d *Device) encodePkt(info *channel.PacketInfo) (buffer.View, bool) {
 	var vv buffer.VectorisedView
 
 	// Packet information.
-	if !d.hasFlags(linux.IFF_NO_PI) {
+	if !d.flags.NoPacketInfo {
 		hdr := make(PacketInfoHeader, PacketInfoHeaderSize)
 		hdr.Encode(&PacketInfoFields{
 			Protocol: info.Proto,
@@ -269,7 +272,7 @@ func (d *Device) encodePkt(info *channel.PacketInfo) (buffer.View, bool) {
 	}
 
 	// Ethernet header (TAP only).
-	if d.hasFlags(linux.IFF_TAP) {
+	if d.flags.TAP {
 		// Add ethernet header if not provided.
 		if info.Pkt.LinkHeader().View().IsEmpty() {
 			d.endpoint.AddHeader(info.Route.LocalLinkAddress, info.Route.RemoteLinkAddress, info.Proto, info.Pkt)
@@ -298,16 +301,12 @@ func (d *Device) Name() string {
 }
 
 // Flags returns the flags set for d. Zero value if unset.
-func (d *Device) Flags() uint16 {
+func (d *Device) Flags() Flags {
 	d.mu.RLock()
 	defer d.mu.RUnlock()
 	return d.flags
 }
 
-func (d *Device) hasFlags(flags uint16) bool {
-	return d.flags&flags == flags
-}
-
 // Readiness implements watier.Waitable.Readiness.
 func (d *Device) Readiness(mask waiter.EventMask) waiter.EventMask {
 	if mask&waiter.EventIn != 0 {
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 18817029d..faca35892 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -323,7 +323,9 @@ func newSender(ep *endpoint, iss, irs seqnum.Value, sndWnd seqnum.Size, mss uint
 // their initial values.
 func (s *sender) initCongestionControl(congestionControlName tcpip.CongestionControlOption) congestionControl {
 	s.sndCwnd = InitialCwnd
-	s.sndSsthresh = math.MaxInt64
+	// Set sndSsthresh to the maximum int value, which depends on the
+	// platform.
+	s.sndSsthresh = int(^uint(0) >> 1)
 
 	switch congestionControlName {
 	case ccCubic: