Remove linux.EpollEvent.Fd.

glibc defines struct epoll_event in such a way that epoll_event.data.fd exists.
However, the kernel's definition of struct epoll_event makes epoll_event.data
an opaque uint64, so naming half of it "fd" just introduces confusion. Remove
the Fd field, and make Data a [2]int32 to compensate.

Also add required padding to linux.EpollEvent on ARM64.

PiperOrigin-RevId: 295250424

4 files changed, 51 insertions, 7 deletions

diff --git a/pkg/abi/linux/BUILD b/pkg/abi/linux/BUILD
index b7015367b..a89f34d4b 100644
--- a/pkg/abi/linux/BUILD
+++ b/pkg/abi/linux/BUILD
@@ -17,6 +17,8 @@ go_library(
         "dev.go",
         "elf.go",
         "epoll.go",
+        "epoll_amd64.go",
+        "epoll_arm64.go",
         "errors.go",
         "eventfd.go",
         "exec.go",
diff --git a/pkg/abi/linux/epoll.go b/pkg/abi/linux/epoll.go
index 0e881aa3c..6e4de69da 100644
--- a/pkg/abi/linux/epoll.go
+++ b/pkg/abi/linux/epoll.go
@@ -14,13 +14,6 @@
 
 package linux
 
-// EpollEvent is equivalent to struct epoll_event from epoll(2).
-type EpollEvent struct {
-	Events uint32
-	Fd     int32
-	Data   int32
-}
-
 // Event masks.
 const (
 	EPOLLIN     = 0x1
diff --git a/pkg/abi/linux/epoll_amd64.go b/pkg/abi/linux/epoll_amd64.go
new file mode 100644
index 000000000..57041491c
--- /dev/null
+++ b/pkg/abi/linux/epoll_amd64.go
@@ -0,0 +1,25 @@
+// Copyright 2019 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.
+
+package linux
+
+// EpollEvent is equivalent to struct epoll_event from epoll(2).
+type EpollEvent struct {
+	Events uint32
+	// Linux makes struct epoll_event::data a __u64. We represent it as
+	// [2]int32 because, on amd64, Linux also makes struct epoll_event
+	// __attribute__((packed)), such that there is no padding between Events
+	// and Data.
+	Data [2]int32
+}
diff --git a/pkg/abi/linux/epoll_arm64.go b/pkg/abi/linux/epoll_arm64.go
new file mode 100644
index 000000000..62ef5821e
--- /dev/null
+++ b/pkg/abi/linux/epoll_arm64.go
@@ -0,0 +1,24 @@
+// Copyright 2020 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.
+
+package linux
+
+// EpollEvent is equivalent to struct epoll_event from epoll(2).
+type EpollEvent struct {
+	Events uint32
+	// Linux makes struct epoll_event a __u64, necessitating 4 bytes of padding
+	// here.
+	_    int32
+	Data [2]int32
+}