syscall, internal/poll: fall back to accept on linux-arm

Our minimum Linux version is 2.6.32, and the accept4 system call was
introduced in 2.6.28, so we use accept4 everywhere. Unfortunately,
it turns out that the accept4 system call was only added to
linux-arm in 2.6.36, so for linux-arm only we need to try the accept4
system call and then fall back to accept if it doesn't work.

The code we use on linux-arm is the code we used in Go 1.17.
On non-arm platforms we continue using the simpler code introduced
in Go 1.18.

Adding accept4 to the ARM Linux kernel was:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=21d93e2e29722d7832f61cc56d73fb953ee6578e

Fixes #57333

Change-Id: I6680cb54dd4d3514a6887dda8906e6708c64459d
Reviewed-on: https://go-review.googlesource.com/c/go/+/457995
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

4 files changed, 71 insertions, 16 deletions

diff --git a/src/syscall/syscall_linux.go b/src/syscall/syscall_linux.go
index bdee570dda..30fa641627 100644
--- a/src/syscall/syscall_linux.go
+++ b/src/syscall/syscall_linux.go
@@ -643,21 +643,6 @@ func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {
 	return nil, EAFNOSUPPORT
 }
 
-func Accept(fd int) (nfd int, sa Sockaddr, err error) {
-	var rsa RawSockaddrAny
-	var len _Socklen = SizeofSockaddrAny
-	nfd, err = accept4(fd, &rsa, &len, 0)
-	if err != nil {
-		return
-	}
-	sa, err = anyToSockaddr(&rsa)
-	if err != nil {
-		Close(nfd)
-		nfd = 0
-	}
-	return
-}
-
 func Accept4(fd int, flags int) (nfd int, sa Sockaddr, err error) {
 	var rsa RawSockaddrAny
 	var len _Socklen = SizeofSockaddrAny
diff --git a/src/syscall/syscall_linux_accept.go b/src/syscall/syscall_linux_accept.go
new file mode 100644
index 0000000000..66c0f84cb8
--- /dev/null
+++ b/src/syscall/syscall_linux_accept.go
@@ -0,0 +1,34 @@
+// 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.
+
+// We require Linux kernel version 2.6.32. The accept4 system call was
+// added in version 2.6.28, so in general we can use accept4.
+// Unfortunately, for ARM only, accept4 was added in version 2.6.36.
+// Handle that case here, by using a copy of the Accept function that
+// we used in Go 1.17.
+
+//go:build linux && arm
+
+package syscall
+
+//sys	accept(s int, rsa *RawSockaddrAny, addrlen *_Socklen) (fd int, err error)
+
+func Accept(fd int) (nfd int, sa Sockaddr, err error) {
+	var rsa RawSockaddrAny
+	var len _Socklen = SizeofSockaddrAny
+	// Try accept4 first for Android and newer kernels.
+	nfd, err = accept4(fd, &rsa, &len, 0)
+	if err == ENOSYS {
+		nfd, err = accept(fd, &rsa, &len)
+	}
+	if err != nil {
+		return
+	}
+	sa, err = anyToSockaddr(&rsa)
+	if err != nil {
+		Close(nfd)
+		nfd = 0
+	}
+	return
+}
diff --git a/src/syscall/syscall_linux_accept4.go b/src/syscall/syscall_linux_accept4.go
new file mode 100644
index 0000000000..74898672c0
--- /dev/null
+++ b/src/syscall/syscall_linux_accept4.go
@@ -0,0 +1,25 @@
+// 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.
+
+// This file provides the Accept function used on all systems
+// other than arm. See syscall_linux_accept.go for why.
+
+//go:build linux && !arm
+
+package syscall
+
+func Accept(fd int) (nfd int, sa Sockaddr, err error) {
+	var rsa RawSockaddrAny
+	var len _Socklen = SizeofSockaddrAny
+	nfd, err = accept4(fd, &rsa, &len, 0)
+	if err != nil {
+		return
+	}
+	sa, err = anyToSockaddr(&rsa)
+	if err != nil {
+		Close(nfd)
+		nfd = 0
+	}
+	return
+}
diff --git a/src/syscall/zsyscall_linux_arm.go b/src/syscall/zsyscall_linux_arm.go
index db5ec60448..69f811a0ec 100644
--- a/src/syscall/zsyscall_linux_arm.go
+++ b/src/syscall/zsyscall_linux_arm.go
@@ -1,4 +1,4 @@
-// mksyscall.pl -l32 -arm -tags linux,arm syscall_linux.go syscall_linux_arm.go
+// mksyscall.pl -l32 -arm -tags linux,arm syscall_linux.go syscall_linux_arm.go syscall_linux_accept.go
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build linux && arm
@@ -1601,3 +1601,14 @@ func setrlimit(resource int, rlim *rlimit32) (err error) {
 	}
 	return
 }
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
+func accept(s int, rsa *RawSockaddrAny, addrlen *_Socklen) (fd int, err error) {
+	r0, _, e1 := Syscall(SYS_ACCEPT, uintptr(s), uintptr(unsafe.Pointer(rsa)), uintptr(unsafe.Pointer(addrlen)))
+	fd = int(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}