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Android Internals - Change Log

Volume I:

The Android Volume I Change Log
DateVersionNotes
3/30/20212.0.1
  • Preface: (BTC is $59k, only a month and a half later.. :-)
  • Chapter 1: Table 1/1-1 - Android versions, with %ages - updated to March 2021 (previous was Feb 2021, though mistakenly said May 2020)
  • Chapter 2:
    • Table 2/4-5 (Samsung Exynos devices) - Added NPU device
      vertex10drivers/vision/npu/npu-vertex.cNPU
      sr100drivers/uwb/sr100.c S21 Ultra: Ultra Wide Band (UWB)
      (Thanks to my good friend _@bazad who wrote about the Exynos NPU vulnerability before being taken by the spaceship)
  • Chapter 3:
    • Table 3/4-1 - (Linux pseudo filesystems actively used by Android 11) - Added BinderFS and filled in missing description for FunctionFS:
      /dev/binderfsbinderfsLinux 5.0+: Dynamic Binder devices (q.v. II/8)
      /dev/usb-ffsfunctionfsUSB functions (Gadget driver)
  • Chapter 4:
    • Table 4/2-2 (Qualcomm /vendor/bin) - Added spdaemon which eluded me because it's not used in Google devices..
      spdaemonSecure Processing Unit (SPU) manager (on non-Google devices)
    • Table 4/2-5 (MTK /vendor/bin) - this was left woefully incomplete. Sorry about that (versioning problem). Here's what it should look like: … (will add this soon)
  • Chapter 8:
    • Added copy_per_line init directive (new in 12.0), and that 'critical' (for services) now takes arguments
    • Table 8/7-1 (cont):
      • Added snapuserd.rc under "System & Volume Management" right after snapshotctl.rc (which it apparently replaces)
      • Filled cppreopts.rc in the table (I had omitted that, sorry)
        cppreopts.rcCopy preoptimized files
  • Chapter 9:
    • Update of Table 9/5-1 with system_server_dumper
    • Added:

      Android 12 adds the system_server_dumper service. As its name implies, this is a dumpsys only service with no clients, listing the properties of SystemServer (start count and elapsed time), SystemServiceManager (started service classes) and the SystemServerInitThreadPool.

      before Figure 9/4-3
    • Added (Before Table 9/3-3, to expand on "dynamic" service lookup):

      The client API of a.os.ServiceManager allows (as of Android 11.0) the waitFor[Declared]Service(svcName) methods.

  • Chapter 10:
    • Table 10/3-6 had some missing fields. Here's all of it:
      Table 10/3-6: The elements in /etc/sysconfig/ and /etc/permissions/ files
      ElementMeaning
      groupGlobal group IDs given to packages (III/2)
      permissionBuilt-in UID to permission mappings (III/2)
      assign-permissionAssign name permission to uid (III/2)
      split-permissionSplit name permission for targetSdk version (III/2)
      library Built-in shared libraries
      [unavailable-]featureIndicate or hide a platform feature (for <uses-feature>)
      allow-in-power-save[-except-idle]Allow package to operate even device is in different power modes
      allow-in-data-usage-save
      allow-unthrottled-locationAllow continuous location updates
      allow-ignore-location-settings Override location settings
      allow-implicit-broadcastExempt broadcast from 8.0 background delivery restrictions
      app-linkAndroid application link (II/3)
      system-user-[black|white]listed-appApp may (or may not) run as system user
      default-enabled-vr-appDefault VR Apps
      component-overrideEnabled component overrides
      backup-transport-whitelisted-servicePermitted backup transport service components
      disabled-until-used-preinstalled
      -carrier[-associated]-app
      Disabled apps
      [privapp/oem]-permissionsAssign extra permissions
      hidden-api-whitelisted-appNon-platform apps allowed access to full private API
      allow-associationAllow target package to interact with allowed package
      app-data-isolation-whitelisted-appApps enabled for data isolation
      bugreport-whitelistedAllow package to generate bug report
      install-in-user-typeInstall package in user-type (FULL/PROFILE)
      named-actorNamed actors (used by Overlay service, q.v. II/3)
      overlay-config-signaturePackage capable of validating config_signature for overlays (q.v. II/3)
      rollback-whitelisted-appApps eligible for enabling rollback
      whitelisted-staged-installerInstallers allowed to commit staged install (II/2)
  • Chapter 13: Thanks to the wonder of writing in HTML, the Google Pixel Powerstats coverage wasn't printed:

    Google documents the IPowerStats.hal in the Source site[psh], and its AIDL is similar. The implementation of the service for Pixel devices (android.hardware.power.stats@1.0-service.pixel) can be found in open source.[psp] Rails data is collected from /sys/bus/iio/devices/iio:device#, and the service recognizes the following power entities:

    Table 13/5-3:: The power entities defined by the Google Pixel powerstats implementation
    EntityProvider path
    RPM (APSS/MPSS/ADSP/
    CDSP/SLPI/SLPI_ISLAND)
    /sys/power/rpmh_stats/master_stats
    SoC/sys/power/system_sleep/stats
    WLAN/sys/kernel/wlan/power_stats
    Pixel Visual Core (AirBrush)/sys/devices/platform/soc/soc:abc-sm/state_stats
    NFC/sys/class/misc/st21nfc/device/power_stats
    GPU/sys/class/kgsl/kgsl-3d0/gpu_clock_stats
    Oslo/dev/iaxxx-module-celldrv (via IAXXX_SENSOR_MODE_STATS ioctl(2))
    IAXXX/dev/iaxxx-module-celldrv (via IAXXX_POWER_STATS_COUNT ioctl(2))
    Citadel (Titan M)AIDL to Citadel service
  • References: As an appendix (which somehow got omitted from the first print batch). Now in print and also online at this link
(11/09/2021) v2.1
  • Preface:
    • BTC is down to $38k $50k$47k $55k $66k. Sheesh
    • Added a GREAT tip for starting ADB with env/startup options specified for shell - Thanks to @KingOfPhp:
  • Chapter 1:
    • Added note: Bionic is also used outside Android (notably in the hardened GrapheneOS), though Fuchsia's libc is derived from musl[musl].
    • Updated Figure 1-3/10 to reflect cases where HIDL server doesn't access hardware directly, but rather through yet another vendor daemon (very popular, and I discuss it in II/8, but somehow illustration didn't reflect it). So now it looks like this:
  • Chapter 2:
    • Updated Table 2/1-1 for ARMv9 launch (happened after v2.0.1 came out...)
      v9A510, A710Confidential Compute Architecture (CCA), SVE2, Transactional Memory Extension (TME)
    • Updated Mediatek chipset table: Dimensity 1000 is UFS 2.2, 1200 is UFS 3.1 and now has Realme devices:

      Dimensity 1000/L/+ (MT6887/9)CPU: 4xA77@2.6Ghz + 4xA55@2.2Ghz
      GPU: ARM Mali-G77 MC9@800Mhz (UFS 2.2)
      6-core APU 3.0
      Oppo Reno3 5G,
      Vivo IQOO Z1 5G
      Dimensity 1200 (MT6893) CPU: 1x A78 3x A77@2.6Ghz + 4xA55@2.2Ghz
      GPU: ARM Mali-G77 MC9@800Mhz (UFS 3.1)
      6-core APU 3.0
      Realme GT Neo, X9 Pro
    • Update Samsung Chipset table with Pixel 6[XL]
    • Also adding /dev/rpmsg_ctrl# - for Linux Remote Processor Messaging, used by QCom
    • 2/4.1.1 - Google Devices (up to but not including Pixel 6) use Qualcomm Chipsets
    • Added footnote for Huawei -

      * - The US imposed ban, along with a worldwide chip shortage in 2021, continue to take its toll on Huawei - it's P50 line of phones not only uses the Qualcomm SnapDragon 888 chipset, but further ships without 5G capabilities. The phones ship with HarmonyOS 2.0.
  • Chapter 3:
    • Android 11 mandates kernels not support debugfs. Somehow I missed that in the A11 release notes, but learned this the hard way trying to run bindump on a redfin (Pixel 5), which comes with A11 as stock. This breaks my bindump tool.
    • Note that packages.xml is now ABX! (also, @@TODO no <perms> element)
  • Chapter 5:
    • Added Google's APEX link:
      Google maintains a comprehensive list for these "modular system components"[msc]
    • Changed Table 5/4-1 (Standard directories created by Android on SD-Cards) to an output
    • Output 5/1-2: The loop mounts of apexd - added ls -l /sys/devices (Thanks, Woody!)

      Output 5/1-2: The loop mounts of apexd
      #
      # filter '@version' entries, differentiating from  non-versioned bind
      mounts
      #
      flame:/ $ mount | grep loop | grep @
      /dev/block/loop6 on /apex/com.android.cellbroadcast@300900702
      type ext4 (ro,dirsync,seclabel,nodev,noatime)
      ..
      /dev/block/loop27 on /apex/com.android.os.statsd@300900700
      type ext4 (ro,dirsync,seclabel,nodev,noatime)
      #
      # The loop-mounted image can be found through the /sys filesystem
      # (though this requires root)
      #
      flame:/ # cat
      /sys/devices/virtual/block/loop10/loop/backing_file
      /system/apex/com.google.android.scheduling.apex
      
  • Chapter 6: Pixel 6[XL] and onward use FBPKv2
  • Chapter 9:
    • Added a table of the Binder default transactions I had originally set for Volume II/7 in place of the paragraph listing them (it made sense, now that 11.0 and 12.0 add even more):

      Table 9/1-2-b: Default Transaction Codes supported by (almost) all Binder objects
      ConstantValueDefault Behavior
      DUMP_TRANSACTION_DMP (1598311760)Requests full dump of service state to specified fd according to optional arguments. Used by dumpsys
      INTERFACE_TRANSACTION_NTF (1598968902)Requests interface of service object behind handle.
      Expects UTF-16 interface name as reply
      SHELL_COMMAND_TRANSACTION_CMD (1598246212)Command interface for /system/bin/cmd
      SYSPROPS_TRANSACTION_SPR (1599295570)Deprecated: Calls libutils's report_sysprop_change() and any property callbacks
      PING_TRANSACTION_PNG (1599098439)Null transaction ensuring service object is alive.
      EXTENSION_TRANSACTION_EXT (1598380116)11.0: Pass an extension BBinder for object
      DEBUG_PID_TRANSACTION_PID (1599097156)11.0: Return service's process identifier (i.e. getpid())
      SET_RPC_CLIENT_TRANSACTION_RPC (1599230019)12.0 (debug builds, #if BINDER_RPC_DEV_SERVERS,) set socket FD
    • Also emphasized webview_zygote does not randomize its address space relative to other Zygote[64] instances.
    • Also added a footnote:
      * - Using interfaces could ostensibly enable a design in which a single service endpoint could support multiple interfaces or "personalities", though in practice Binder associates a single interface name with an endpoint.
    • @TODO: I'll update Output 9/4-4 (Threads of system_server for new service threads in 12 once the dust settles)
    • Added NativeTombstoneManager to LocalServices table (9/5-4) (realized I had missed it earlier since it came into 11.0 but I now discuss tombstones now in II/1):

      c.a.s.os.NativeTombstoneManager11.0: Manage tombstones and parse protobuf (.pb) tombstones (II/1)
  • Chapter 10: Added people service
  • Chapter 11:
    • In 2.4 (Task profiles), after 11/2-16:

      On kernels which support it, libprocessgroup also adjust /proc/pid/timerslack_ns, which helps coalesce task wakeups, conserving battery life.

    • In lmkd:

      The daemon can thus adjust the "killability" of processes based on the activity state, or other factors (background threads, application services, etc). Google describes the considerations in the ActivityManagerService's OOMAdjuster documentation.[ooma]

    • Added performance_hint details (IHintSession, etc. and dumpsys performance_hint from a Pixel 6)
  • Chapter 12: android.hardware.dumpstate@1.1:IDumpstateDevice.hal is version 1.1
  • Chapter 13: (before 13/4-5, after mention of msm_adreno_tz) added "… and other governors in /sys/kernel/gpu/gpu_available_governor"
  • (thankfully very few) typos found by James H (thank you! - see below)
  • on page 291 paragraph 3, it is stated that "ps -t" on Android will list Thread. Should be "-T"... (Thanks, John Zou!)







*Sigh* Typos: (These don't get you the BTC bounty, but I still appreciate them!)