Add order file sample.

I took the PGO and Camera example and added order file functionalities
to them. I added steps so people can figure out how to add order file to
their own Android application.

orderfile/README.md

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+# Order file demo
+
+Order files are text files containing symbols representing functions names.
+Linkers (lld) uses order files to layout functions in a specific order. These
+binaries with ordered symbols will reduce page faults and improve a program's
+launch time due to the efficient loading of symbols during a program’s
+cold-start.
+
+## Files
+
+- app/src/main/cpp/orderfile.cpp: The source code for the orderfile library that
+  is used by the Kotlin app.
+- app/src/main/cpp/CMakeLists.txt: The CMakeLists either sets the orderfile
+  library as generating profiles or loading the orderfile.
+- app/src/main/java/MainActivity.kt: The Kotlin app source code.
+
+## Profile Steps
+
+1. For simplicity, we have setup the `CMakeLists.txt` and you just need make
+   sure `set(GENERATE_PROFILES ON)` is not commented. You need to pass any
+   optimization flag except `-O0`. The mapping file is not generated and the
+   profile instrumentation does not work without an optimization flag.
+1. Run the app on Android Studio. You can either run it on a physical or virtual
+   device. You will see "Hello World" on the screen.
+1. To pull the data from the device, you'll need to move it from an app-writable
+   directory to a shell readable directory for adb pull. We also need to
+   transfer the output into hexadecimal format.
+
+```
+adb shell "run-as com.example.orderfiledemo sh -c 'cat /data/user/0/com.example.orderfiledemo/cache/demo.output.order' | cat > /data/local/tmp/demo.output.order"
+adb pull /data/local/tmp/demo.output.order .
+
+# Convert to hexdeciaml format on Linux, Mac, or ChromeOS
+hexdump -C demo.output.order > demo.prof
+
+# Convert to hexdecimal format on Windows
+certutil -f -encodeHex demo.output.order demo.prof
+```
+
+4. Once you get both mapping file and profile file, you can use
+   [this script](https://android.googlesource.com/toolchain/pgo-profiles/+/refs/heads/main/scripts/create_orderfile.py)
+   to create the order file:
+
+```
+python3 create_orderfile.py --profile-file demo.prof --mapping-file mapping.txt --output app/src/main/cpp/demo.orderfile
+```
+
+## Load Steps
+
+1. For load, you need to uncomment
+   `set(USE_PROFILE "${CMAKE_SOURCE_DIR}/demo.orderfile")` and make sure
+   `set(GENERATE_PROFILES ON)` is commented.
+
+1. If you want to validate the shared library's layout is different, you need to
+   find `liborderfiledemo.so` and run `nm`
+
+```
+nm -n liborderfiledemo.so
+```
+
+## Difference between Java and Kotlin App
+
+The main difference between a Java app and a Kotlin app is the syntax. You can
+easily change this Kotlin example into a Java example.
+
+- Load Library
+
+```
+# Kotlin
+companion object {
+    init {
+        System.loadLibrary("orderfiledemo")
+    }
+}
+
+# Java
+static {
+    System.loadLibrary("orderfiledemo");
+}
+```
+
+- Recognize an external method
+
+```
+# Kotlin
+external fun runWorkload(tempDir: String)
+
+# Java
+private native void runWorkload(String tempDir);
+```
+
+- Get the cache directory
+
+```agsl
+# Kotlin
+runWorkload(applicationContext.cacheDir.toString())
+
+# Java
+runWorkload(getcacheDir().toString())
+```

orderfile/app/.gitignore

@@ -0,0 +1 @@
+/build

orderfile/app/build.gradle

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+plugins {
+    id 'com.android.application'
+    id 'kotlin-android'
+}
+
+android {
+    compileSdk 31
+
+    defaultConfig {
+        applicationId "com.example.orderfiledemo"
+        minSdk 21
+        targetSdk 31
+        versionCode 1
+        versionName "1.0"
+        ndkVersion '25.2.9519653'
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        externalNativeBuild {
+            cmake {
+                cppFlags ''
+            }
+        }
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+    externalNativeBuild {
+        cmake {
+            path file('src/main/cpp/CMakeLists.txt')
+            version '3.22.1'
+        }
+    }
+    buildFeatures {
+        viewBinding true
+    }
+    namespace 'com.example.orderfiledemo'
+    ndkVersion '25.2.9519653'
+}
+
+dependencies {
+
+    implementation 'androidx.core:core-ktx:1.3.2'
+    implementation 'androidx.appcompat:appcompat:1.2.0'
+    implementation 'com.google.android.material:material:1.3.0'
+    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
+    testImplementation 'junit:junit:4.+'
+    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
+    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
+}

orderfile/app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

orderfile/app/src/androidTest/java/com/example/orderfiledemo/ExampleInstrumentedTest.kt

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+package com.example.orderfiledemo
+
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.ext.junit.runners.AndroidJUnit4
+
+import org.junit.Test
+import org.junit.runner.RunWith
+
+import org.junit.Assert.*
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+    @Test
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
+        assertEquals("com.example.orderfiledemo", appContext.packageName)
+    }
+}

orderfile/app/src/main/AndroidManifest.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.OrderfileDemo">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>

orderfile/app/src/main/cpp/CMakeLists.txt

@@ -0,0 +1,25 @@
+cmake_minimum_required(VERSION 3.22.1)
+project(OrderfileDemo CXX)
+
+# We have setup build variables that you can just comment or uncomment to use.
+# Make sure to have only one build variable uncommented at a time.
+# If you want to generate profiles and mapping file, make sure GENERATE_PROFILES is uncommented.
+# If you want to use your generated order file to layout symbols, uncomment USE_PROFILE.
+
+
+set(GENERATE_PROFILES ON)
+#set(USE_PROFILE "${CMAKE_SOURCE_DIR}/demo.orderfile")
+
+add_library(orderfiledemo SHARED orderfile.cpp)
+target_link_libraries(orderfiledemo log)
+
+if(GENERATE_PROFILES)
+    # Generating profiles requires any optimization flag aside from -O0.
+    # The mapping file will not generate and the profile instrumentation does not work without an optimization flag. 
+    target_compile_options(orderfiledemo PRIVATE -forder-file-instrumentation -O1 -mllvm -orderfile-write-mapping=mapping.txt )
+    target_link_options(orderfiledemo PRIVATE -forder-file-instrumentation )
+    target_compile_definitions(orderfiledemo PRIVATE GENERATE_PROFILES)
+elseif(USE_PROFILE)
+    target_compile_options(orderfiledemo PRIVATE -Wl,--symbol-ordering-file=${USE_PROFILE} -Wl,--no-warn-symbol-ordering )
+    target_link_options(orderfiledemo PRIVATE -Wl,--symbol-ordering-file=${USE_PROFILE} -Wl,--no-warn-symbol-ordering )
+endif()

orderfile/app/src/main/cpp/orderfile.cpp

@@ -0,0 +1,54 @@
+#include <android/log.h>
+#include <errno.h>
+#include <jni.h>
+#include <linux/limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+const char kLogTag[] = "orderfiledemo";
+
+#ifdef GENERATE_PROFILES
+extern "C" int __llvm_profile_set_filename(const char *);
+extern "C" int __llvm_profile_initialize_file(void);
+extern "C" int __llvm_orderfile_dump(void);
+#endif
+
+void DumpProfileDataIfNeeded(const char *temp_dir) {
+#ifdef GENERATE_PROFILES
+  char profile_location[PATH_MAX] = {};
+  snprintf(profile_location, sizeof(profile_location), "%s/demo.output",
+           temp_dir);
+  if (__llvm_profile_set_filename(profile_location) == -1) {
+    __android_log_print(ANDROID_LOG_ERROR, kLogTag,
+                        "__llvm_profile_set_filename(\"%s\") failed: %s",
+                        profile_location, strerror(errno));
+    return;
+  }
+
+  if (__llvm_profile_initialize_file() == -1) {
+    __android_log_print(ANDROID_LOG_ERROR, kLogTag,
+                        "__llvm_profile_initialize_file failed: %s",
+                        strerror(errno));
+    return;
+  }
+
+  if (__llvm_orderfile_dump() == -1) {
+    __android_log_print(ANDROID_LOG_ERROR, kLogTag,
+                        "__llvm_orderfile_dump() failed: %s", strerror(errno));
+    return;
+  }
+  __android_log_print(ANDROID_LOG_DEBUG, kLogTag, "Wrote profile data to %s",
+                      profile_location);
+#else
+  __android_log_print(ANDROID_LOG_DEBUG, kLogTag,
+                      "Did not write profile data because the app was not "
+                      "built for profile generation");
+#endif
+}
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_example_orderfiledemo_MainActivity_runWorkload(JNIEnv *env,
+                                                        jobject /* this */,
+                                                        jstring temp_dir) {
+  DumpProfileDataIfNeeded(env->GetStringUTFChars(temp_dir, 0));
+}

orderfile/app/src/main/java/com/example/orderfiledemo/MainActivity.kt

@@ -0,0 +1,32 @@
+package com.example.orderfiledemo 
+
+import androidx.appcompat.app.AppCompatActivity
+import android.os.Bundle
+import com.example.orderfiledemo .databinding.ActivityMainBinding
+
+class MainActivity : AppCompatActivity() {
+
+    private lateinit var binding: ActivityMainBinding
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+
+        binding = ActivityMainBinding.inflate(layoutInflater)
+        setContentView(binding.root)
+        runWorkload(applicationContext.cacheDir.toString())
+        binding.sampleText.text = "Hello, world!"
+    }
+
+    /**
+     * A native method that is implemented by the 'orderfiledemo' native library,
+     * which is packaged with this application.
+     */
+    external fun runWorkload(tempDir: String)
+
+    companion object {
+        // Used to load the 'orderfiledemo' library on application startup.
+        init {
+            System.loadLibrary("orderfiledemo")
+        }
+    }
+}

orderfile/app/src/main/res/drawable-v24/ic_launcher_foreground.xml

@@ -0,0 +1,30 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:aapt="http://schemas.android.com/aapt"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path android:pathData="M31,63.928c0,0 6.4,-11 12.1,-13.1c7.2,-2.6 26,-1.4 26,-1.4l38.1,38.1L107,108.928l-32,-1L31,63.928z">
+        <aapt:attr name="android:fillColor">
+            <gradient
+                android:endX="85.84757"
+                android:endY="92.4963"
+                android:startX="42.9492"
+                android:startY="49.59793"
+                android:type="linear">
+                <item
+                    android:color="#44000000"
+                    android:offset="0.0" />
+                <item
+                    android:color="#00000000"
+                    android:offset="1.0" />
+            </gradient>
+        </aapt:attr>
+    </path>
+    <path
+        android:fillColor="#FFFFFF"
+        android:fillType="nonZero"
+        android:pathData="M65.3,45.828l3.8,-6.6c0.2,-0.4 0.1,-0.9 -0.3,-1.1c-0.4,-0.2 -0.9,-0.1 -1.1,0.3l-3.9,6.7c-6.3,-2.8 -13.4,-2.8 -19.7,0l-3.9,-6.7c-0.2,-0.4 -0.7,-0.5 -1.1,-0.3C38.8,38.328 38.7,38.828 38.9,39.228l3.8,6.6C36.2,49.428 31.7,56.028 31,63.928h46C76.3,56.028 71.8,49.428 65.3,45.828zM43.4,57.328c-0.8,0 -1.5,-0.5 -1.8,-1.2c-0.3,-0.7 -0.1,-1.5 0.4,-2.1c0.5,-0.5 1.4,-0.7 2.1,-0.4c0.7,0.3 1.2,1 1.2,1.8C45.3,56.528 44.5,57.328 43.4,57.328L43.4,57.328zM64.6,57.328c-0.8,0 -1.5,-0.5 -1.8,-1.2s-0.1,-1.5 0.4,-2.1c0.5,-0.5 1.4,-0.7 2.1,-0.4c0.7,0.3 1.2,1 1.2,1.8C66.5,56.528 65.6,57.328 64.6,57.328L64.6,57.328z"
+        android:strokeWidth="1"
+        android:strokeColor="#00000000" />
+</vector>