diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index edda3919..77d1f56f 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -152,7 +152,12 @@ page at http://checkstyle.sourceforge.net/config.html -->
       <property name="severity" value="info" />
     </module>
     <module name="UpperEll" />
+  </module>
 
+  <!-- Excludes android.system polyfill.                  -->
+  <!-- See https://checkstyle.org/config_filefilters.html -->
+  <module name="BeforeExecutionExclusionFileFilter">
+    <property name="fileNamePattern" value=".*[\\/]java[\\/]android[\\/]system[\\/].*$" />
   </module>
 
 </module>
diff --git a/libcore/build.gradle b/libcore/build.gradle
new file mode 100644
index 00000000..9900fd60
--- /dev/null
+++ b/libcore/build.gradle
@@ -0,0 +1 @@
+apply plugin: 'java-library'
diff --git a/libcore/src/main/java/libcore/io/ErrnoException.java b/libcore/src/main/java/libcore/io/ErrnoException.java
new file mode 100644
index 00000000..be89321a
--- /dev/null
+++ b/libcore/src/main/java/libcore/io/ErrnoException.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 libcore.io;
+
+/**
+ * A checked exception thrown when {@link Os} methods fail. This exception contains the native
+ * errno value, for comparison against the constants in {@link OsConstants}, should sophisticated
+ * callers need to adjust their behavior based on the exact failure.
+ */
+public final class ErrnoException extends Exception {
+    private final String functionName;
+    public final int errno;
+
+    public ErrnoException(String functionName, int errno) {
+        throw new AssertionError();
+    }
+}
diff --git a/libcore/src/main/java/libcore/io/Libcore.java b/libcore/src/main/java/libcore/io/Libcore.java
new file mode 100644
index 00000000..0231ecb5
--- /dev/null
+++ b/libcore/src/main/java/libcore/io/Libcore.java
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 libcore.io;
+
+public final class Libcore {
+    private Libcore() {
+    }
+
+    public static Os os = null;
+}
diff --git a/libcore/src/main/java/libcore/io/Os.java b/libcore/src/main/java/libcore/io/Os.java
new file mode 100644
index 00000000..4a9e61a8
--- /dev/null
+++ b/libcore/src/main/java/libcore/io/Os.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 libcore.io;
+
+import java.io.FileDescriptor;
+import java.nio.ByteBuffer;
+
+public interface Os {
+    public String strerror(int errno);
+
+    public int write(FileDescriptor fd, ByteBuffer buffer) throws ErrnoException;
+}
diff --git a/libcore/src/main/java/libcore/io/OsConstants.java b/libcore/src/main/java/libcore/io/OsConstants.java
new file mode 100644
index 00000000..ea0af53b
--- /dev/null
+++ b/libcore/src/main/java/libcore/io/OsConstants.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 libcore.io;
+
+public final class OsConstants {
+    private OsConstants() {
+    }
+
+    public static final int EINTR = placeholder();
+
+    public static String errnoName(int errno) {
+        return null;
+    }
+
+    // A hack to avoid these constants being inlined by javac...
+    private static int placeholder() { return 0; }
+}
diff --git a/server/build.gradle b/server/build.gradle
index 67591e5b..dd7591e2 100644
--- a/server/build.gradle
+++ b/server/build.gradle
@@ -22,6 +22,7 @@ dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
     testImplementation 'junit:junit:4.13.1'
     compileOnly rootProject.fileTree("thirdparty/androidx/annotation/1.3.0/annotation-1.3.0.jar")
+    compileOnly project(':libcore')
 }
 
 apply from: "$project.rootDir/config/android-checkstyle.gradle"
diff --git a/server/build_without_gradle.sh b/server/build_without_gradle.sh
index e41e8e59..e4202e74 100755
--- a/server/build_without_gradle.sh
+++ b/server/build_without_gradle.sh
@@ -54,6 +54,8 @@ classpath="$CLASSES_DIR"
 classpath="$classpath:$ROOT_PROJECT_DIR/thirdparty/androidx/annotation/1.3.0/annotation-1.3.0.jar"
 javac -bootclasspath "$ANDROID_JAR" -cp "$classpath" -d "$CLASSES_DIR" \
     -source 1.8 -target 1.8 \
+    android/system/*.java \
+    $ROOT_PROJECT_DIR/libcore/src/main/java/libcore/io/*.java \
     com/genymobile/scrcpy/*.java \
     com/genymobile/scrcpy/wrappers/*.java
 
@@ -65,6 +67,7 @@ then
     # use dx
     "$ANDROID_HOME/build-tools/$BUILD_TOOLS/dx" --dex \
         --output "$BUILD_DIR/classes.dex" \
+        android/system/*.class \
         android/view/*.class \
         android/content/*.class \
         com/genymobile/scrcpy/*.class \
@@ -78,6 +81,7 @@ else
     # use d8
     "$ANDROID_HOME/build-tools/$BUILD_TOOLS/d8" --classpath "$ANDROID_JAR" \
         --output "$BUILD_DIR/classes.zip" \
+        android/system/*.class \
         android/view/*.class \
         android/content/*.class \
         com/genymobile/scrcpy/*.class \
diff --git a/server/src/main/java/android/system/ErrnoException.java b/server/src/main/java/android/system/ErrnoException.java
new file mode 100644
index 00000000..75d90193
--- /dev/null
+++ b/server/src/main/java/android/system/ErrnoException.java
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 android.system;
+
+import android.annotation.TargetApi;
+
+import java.io.IOException;
+import java.net.SocketException;
+
+import libcore.io.Libcore;
+
+/**
+ * A checked exception thrown when {@link Os} methods fail. This exception contains the native
+ * errno value, for comparison against the constants in {@link OsConstants}, should sophisticated
+ * callers need to adjust their behavior based on the exact failure.
+ */
+@SuppressWarnings("unused")
+@TargetApi(21)
+public final class ErrnoException extends Exception {
+    private final String functionName;
+
+    /**
+     * The errno value, for comparison with the {@code E} constants in {@link OsConstants}.
+     */
+    public final int errno;
+
+    /**
+     * Constructs an instance with the given function name and errno value.
+     */
+    public ErrnoException(String functionName, int errno) {
+        this.functionName = functionName;
+        this.errno = errno;
+    }
+
+    /**
+     * Constructs an instance with the given function name, errno value, and cause.
+     */
+    public ErrnoException(String functionName, int errno, Throwable cause) {
+        super(cause);
+        this.functionName = functionName;
+        this.errno = errno;
+    }
+
+    /**
+     * Converts the stashed function name and errno value to a human-readable string.
+     * We do this here rather than in the constructor so that callers only pay for
+     * this if they need it.
+     */
+    @Override public String getMessage() {
+        String errnoName = OsConstants.errnoName(errno);
+        if (errnoName == null) {
+            errnoName = "errno " + errno;
+        }
+        String description = Libcore.os.strerror(errno);
+        return functionName + " failed: " + errnoName + " (" + description + ")";
+    }
+
+    /**
+     * Throws an {@link IOException} with a message based on {@link #getMessage()} and with this
+     * instance as the cause.
+     *
+     * <p>This method always terminates by throwing the exception. Callers can write
+     * {@code throw e.rethrowAsIOException()} to make that clear to the compiler.
+     */
+    public IOException rethrowAsIOException() throws IOException {
+        IOException newException = new IOException(getMessage());
+        newException.initCause(this);
+        throw newException;
+    }
+
+    /**
+     * Throws a {@link SocketException} with a message based on {@link #getMessage()} and with this
+     * instance as the cause.
+     *
+     * <p>This method always terminates by throwing the exception. Callers can write
+     * {@code throw e.rethrowAsIOException()} to make that clear to the compiler.
+     */
+    public SocketException rethrowAsSocketException() throws SocketException {
+        final SocketException newException = new SocketException(getMessage());
+        newException.initCause(this);
+        throw newException;
+    }
+}
diff --git a/server/src/main/java/android/system/Os.java b/server/src/main/java/android/system/Os.java
new file mode 100644
index 00000000..456179ca
--- /dev/null
+++ b/server/src/main/java/android/system/Os.java
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 android.system;
+
+import android.annotation.TargetApi;
+
+import java.io.FileDescriptor;
+import java.io.InterruptedIOException;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
+import java.net.SocketException;
+import java.nio.ByteBuffer;
+
+import libcore.io.Libcore;
+
+/**
+ * Access to low-level system functionality. Most of these are system calls. Most users will want
+ * to use higher-level APIs where available, but this class provides access to the underlying
+ * primitives used to implement the higher-level APIs.
+ *
+ * <p>The corresponding constants can be found in {@link OsConstants}.
+ */
+@SuppressWarnings("unused")
+@TargetApi(21)
+public final class Os {
+  private Os() {}
+
+  /**
+   * See <a href="http://man7.org/linux/man-pages/man2/write.2.html">write(2)</a>.
+   */
+  public static int write(FileDescriptor fd, ByteBuffer buffer) throws ErrnoException, InterruptedIOException {
+    try {
+      return Libcore.os.write(fd, buffer);
+    } catch (libcore.io.ErrnoException e) {
+      throw new ErrnoException("write", e.errno);
+    }
+  }
+}
diff --git a/server/src/main/java/android/system/OsConstants.java b/server/src/main/java/android/system/OsConstants.java
new file mode 100644
index 00000000..8580c6b6
--- /dev/null
+++ b/server/src/main/java/android/system/OsConstants.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 android.system;
+
+import android.annotation.TargetApi;
+
+@SuppressWarnings("unused")
+@TargetApi(21)
+public final class OsConstants {
+
+    private OsConstants() { }
+
+    public static final int EINTR = libcore.io.OsConstants.EINTR;
+
+    /**
+     * Returns the string name of an errno value.
+     * For example, "EACCES". See {@link Os#strerror} for human-readable errno descriptions.
+     */
+    public static String errnoName(int errno) {
+        return libcore.io.OsConstants.errnoName(errno);
+    }
+}
diff --git a/server/src/main/java/com/genymobile/scrcpy/IO.java b/server/src/main/java/com/genymobile/scrcpy/IO.java
index 57c017db..bc2f37bd 100644
--- a/server/src/main/java/com/genymobile/scrcpy/IO.java
+++ b/server/src/main/java/com/genymobile/scrcpy/IO.java
@@ -1,5 +1,6 @@
 package com.genymobile.scrcpy;
 
+import android.annotation.TargetApi;
 import android.system.ErrnoException;
 import android.system.Os;
 import android.system.OsConstants;
@@ -13,6 +14,7 @@ public final class IO {
         // not instantiable
     }
 
+    @TargetApi(21) // Backported subset of android.system.
     public static void writeFully(FileDescriptor fd, ByteBuffer from) throws IOException {
         // ByteBuffer position is not updated as expected by Os.write() on old Android versions, so
         // count the remaining bytes manually.
diff --git a/settings.gradle b/settings.gradle
index 8f51035f..31c8f101 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -1 +1,2 @@
 include ':server'
+include ':libcore'