6 files changed, 79 insertions, 42 deletions
diff --git a/pkg/tcpip/link/rawfile/BUILD b/pkg/tcpip/link/rawfile/BUILD
index 11ba31ca4..088eb8a21 100644
--- a/pkg/tcpip/link/rawfile/BUILD
+++ b/pkg/tcpip/link/rawfile/BUILD
@@ -7,8 +7,9 @@ go_library(
     srcs = [
         "blockingpoll_amd64.s",
         "blockingpoll_arm64.s",
+        "blockingpoll_noyield_unsafe.go",
         "blockingpoll_unsafe.go",
-        "blockingpoll_stub_unsafe.go",
+        "blockingpoll_yield_unsafe.go",
         "errors.go",
         "rawfile_unsafe.go",
     ],
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_arm64.s b/pkg/tcpip/link/rawfile/blockingpoll_arm64.s
index 0bc873a01..b62888b93 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_arm64.s
+++ b/pkg/tcpip/link/rawfile/blockingpoll_arm64.s
@@ -1,4 +1,4 @@
-// Copyright 2019 The gVisor Authors.
+// Copyright 2018 The gVisor Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_stub_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_noyield_unsafe.go
index 621ab8d29..621ab8d29 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_stub_unsafe.go
+++ b/pkg/tcpip/link/rawfile/blockingpoll_noyield_unsafe.go
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
index eeca47d78..84dc0e918 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
+++ b/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
@@ -12,49 +12,20 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build linux,amd64 linux,arm64
-// +build go1.12
-// +build !go1.14
-
-// Check go:linkname function signatures when updating Go version.
+// +build linux,!amd64
 
 package rawfile
 
 import (
 	"syscall"
-	_ "unsafe" // for go:linkname
+	"unsafe"
 )
 
-//go:noescape
-func BlockingPoll(fds *PollEvent, nfds int, timeout *syscall.Timespec) (int, syscall.Errno)
-
-// Use go:linkname to call into the runtime. As of Go 1.12 this has to
-// be done from Go code so that we make an ABIInternal call to an
-// ABIInternal function; see https://golang.org/issue/27539.
-
-// We need to call both entersyscallblock and exitsyscall this way so
-// that the runtime's check on the stack pointer lines up.
-
-// Note that calling an unexported function in the runtime package is
-// unsafe and this hack is likely to break in future Go releases.
-
-//go:linkname entersyscallblock runtime.entersyscallblock
-func entersyscallblock()
-
-//go:linkname exitsyscall runtime.exitsyscall
-func exitsyscall()
-
-// These forwarding functions must be nosplit because 1) we must
-// disallow preemption between entersyscallblock and exitsyscall, and
-// 2) we have an untyped assembly frame on the stack which can not be
-// grown or moved.
-
-//go:nosplit
-func callEntersyscallblock() {
-	entersyscallblock()
-}
+// BlockingPoll is just a stub function that forwards to the ppoll() system call
+// on non-amd64 platforms.
+func BlockingPoll(fds *PollEvent, nfds int, timeout *syscall.Timespec) (int, syscall.Errno) {
+	n, _, e := syscall.Syscall6(syscall.SYS_PPOLL, uintptr(unsafe.Pointer(fds)),
+		uintptr(nfds), uintptr(unsafe.Pointer(timeout)), 0, 0, 0)
 
-//go:nosplit
-func callExitsyscall() {
-	exitsyscall()
+	return int(n), e
 }
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go
new file mode 100644
index 000000000..dda3b10a6
--- /dev/null
+++ b/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go
@@ -0,0 +1,66 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build linux,amd64 linux,arm64
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
+package rawfile
+
+import (
+	"syscall"
+	_ "unsafe" // for go:linkname
+)
+
+// BlockingPoll on amd64/arm64 makes the ppoll() syscall while calling the
+// version of entersyscall that relinquishes the P so that other Gs can
+// run. This is meant to be called in cases when the syscall is expected to
+// block. On non amd64/arm64 platforms it just forwards to the ppoll() system
+// call.
+//
+//go:noescape
+func BlockingPoll(fds *PollEvent, nfds int, timeout *syscall.Timespec) (int, syscall.Errno)
+
+// Use go:linkname to call into the runtime. As of Go 1.12 this has to
+// be done from Go code so that we make an ABIInternal call to an
+// ABIInternal function; see https://golang.org/issue/27539.
+
+// We need to call both entersyscallblock and exitsyscall this way so
+// that the runtime's check on the stack pointer lines up.
+
+// Note that calling an unexported function in the runtime package is
+// unsafe and this hack is likely to break in future Go releases.
+
+//go:linkname entersyscallblock runtime.entersyscallblock
+func entersyscallblock()
+
+//go:linkname exitsyscall runtime.exitsyscall
+func exitsyscall()
+
+// These forwarding functions must be nosplit because 1) we must
+// disallow preemption between entersyscallblock and exitsyscall, and
+// 2) we have an untyped assembly frame on the stack which can not be
+// grown or moved.
+
+//go:nosplit
+func callEntersyscallblock() {
+	entersyscallblock()
+}
+
+//go:nosplit
+func callExitsyscall() {
+	exitsyscall()
+}
diff --git a/pkg/tcpip/link/sniffer/sniffer.go b/pkg/tcpip/link/sniffer/sniffer.go
index fc584c6a4..36c8c46fc 100644
--- a/pkg/tcpip/link/sniffer/sniffer.go
+++ b/pkg/tcpip/link/sniffer/sniffer.go
@@ -360,10 +360,9 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, b buffer.Vie
 		if fragmentOffset == 0 && len(udp) >= header.UDPMinimumSize {
 			srcPort = udp.SourcePort()
 			dstPort = udp.DestinationPort()
+			details = fmt.Sprintf("xsum: 0x%x", udp.Checksum())
+			size -= header.UDPMinimumSize
 		}
-		size -= header.UDPMinimumSize
-
-		details = fmt.Sprintf("xsum: 0x%x", udp.Checksum())
 
 	case header.TCPProtocolNumber:
 		transName = "tcp"