不一样的SYSTEM APP(SYSTEM flag和system_prop区别)

1.问题引入

在Android开发中,
1)Framework中PackageManager扫包后,会把app归类为SYSTEM, SYSTEM_EXT, PRIVILEGED 类别.

2)同样的, SeAndroid也会把APP归类程platform_app, system_app, untrusted_app(甚至还有其他,mediaprovider,gmscore_app).

flag SYSTEM和system_app我们都称之为系统app.
但是他们不是同一个概念的"系统app".

2.PackageSettings flag SYSTEM

dumpsys package com.android.systemui为例, 输出如下:

Packages:
  Package [com.android.systemui] (d6f33bf):
    appId=10187
    sharedUser=SharedUserSetting{
   4058ad4 android.uid.systemui/10187}
    pkg=Package{
   aa0e47d com.android.systemui}
    codePath=/system_ext/priv-app/SystemUI
    resourcePath=/system_ext/priv-app/SystemUI
    legacyNativeLibraryDir=/system_ext/priv-app/SystemUI/lib
    extractNativeLibs=true
    primaryCpuAbi=arm64-v8a
    secondaryCpuAbi=null
    cpuAbiOverride=null
    versionCode=1410014 minSdk=33 targetSdk=34
    minExtensionVersions=[]
    versionName=14.00.14
    usesNonSdkApi=false
    splits=[base]
    apkSigningVersion=3
    flags=[ SYSTEM HAS_CODE PERSISTENT ]
    privateFlags=[ PRIVATE_FLAG_ACTIVITIES_RESIZE_MODE_RESIZEABLE_VIA_SDK_VERSION ALLOW_AUDIO_PLAYBACK_CAPTURE DEFAULT_TO_DEVICE_PROTECTED_STORAGE DIRECT_BOOT_AWARE PARTIALLY_DIRECT_BOOT_AWARE PRIVILEGED SYSTEM_EXT PRIVATE_FLAG_ALLOW_NATIVE_HEAP_POINTER_TAGGING ]
    forceQueryable=false

根据输出可以看到两个重要的flag,分别为flags和privateFlags.其中flags其中标签为SYSTEM和PERSISTENT, 而privateFlags其中两个输出为PRIVILEGED/SYSTEM_EXT.

对应的输出代码如下:

    @NeverCompile // Avoid size overhead of debugging code.
    void dumpPackageLPr(PrintWriter pw, String prefix, String checkinTag,
            ArraySet<String> permissionNames, PackageSetting ps,
            LegacyPermissionState permissionsState, SimpleDateFormat sdf, Date date,
            List<UserInfo> users, boolean dumpAll, boolean dumpAllComponents) {
   
        AndroidPackage pkg = ps.getPkg();
        // 省略好多

        if (pkg != null) {
   
            pw.print(prefix); pw.print("  versionName="); pw.println(pkg.getVersionName());
            pw.print(prefix); pw.print(