This document explains what is ARM Cortex-A53 (64bit ARMv8 procesor) errata from AOSP (Android Open Source Project) commit observation and what's going on for the errata as AOSP, what is expected action by each role; device manufacturers and application developers.

1. ARM Cortex-A53 errata on
Android
@hidenorly

2. Official ARM Cortex-A53 information

3. Summary of the errata
● There are critical errata on early verson of
Cortex-A53.
○ The errata are only caused in AArch64.
■ Erratum 835769
■ Erratum 843419
○ These are for A53 only, not on A57/Denver (nVIDIA).
● The solution for the errata is workaround to
avoid the condition by changing the native
code sequence.

4. Errata description from AOSP commit
Erratum 835769.
● https://android-review.googlesource.
com/#/c/113144/
● AArch64: Addressing Cortex-A53 erratum
835769.
● Some early revisions of the Cortex-A53
have an erratum (835769) whereby
● it is possible for a 64-bit multiply-
accumulate instruction in AArch64 state to
generate an incorrect result.
Erratum 843419
● https://android-review.googlesource.
com/#/c/144580/
● [AArch64] Workaround for cortex-a53
erratum 843419
● Some early revisions of the Cortex-A53
have an erratum (843419).
● The details of the erratum are quite
complex and involve dynamic conditions.
For the purposes of the workaround we
have simplified the static conditions to an
ADRP in the last two instructions of a
4KByte page, followed within four
instructions by a load/store dependent on
the ADRP.

5. Default 64bit Andoid device configuration
brings the ARM errata problematic situation
● Most of 64bit Android devices configure with
init.zygote64_32.rc
● And ABI list are configured as
○ [ro.product.cpu.abilist]: [arm64-v8a,armeabi-v7a,
armeabi] (from Nexus 9)
Pure Java app will be executing in AArch64 with ART.

6. Execution mode on abilist=armv8, armeabiv7
Executing mode 32bit native library 64bit native library Render Script
64bit none none none
32bit exist none none
32bit none none exist
32bit exist exist exist
64bit exist exist none
Currently, if the apk has 32bit only native libary or the app uses render script, the application will
be executing in 32bit. But the RenderScript limitation might be changed future platform.
The errata might be affected to most of applications on 64bit ARM system.

7. Cases to hit the errata
Type of code Why? Workaround? Availablity @
25 April 2015
Pure Java code ART compiles dex to AArch64
machine code
Require to patch workaround for
ART by device manufacture side
Depends on
device
Native library for
lib/arm64/
Old toolchain generates the
problematic code for the errata
Recompile with workaround
enabled toolchain (NDK) by app
developer side.
Partially but
not fully
available on
NDK
Java Script with
ChromiumWebView
ChromiumWebView is executing
in AArch64 mode if your app is
running in AArch64.
Accept to use updated version of
System WebView through
Google Play
Not available
Java Script with
Chrome
Chrome is executing in AArch64
on 64bit system
Accept to use updated version of
Chrome through Google Play
Not available

8. Workaround on ART for device FW
platform/art
erratum 835769 https://android-review.googlesource.com/#/c/113144/
https://android-review.googlesource.com/#/c/118930/
erratum 843419 https://android-review.googlesource.com/#/c/145099/
https://android-review.googlesource.com/#/c/144632/
Please note that ADRP is not used on L MR0 / MR1.
And then patches for 843419 are not needed.

9. Tool chain to build device FW
binutils
erratum 835769 https://android-review.googlesource.com/#/c/112784/
https://android-review.googlesource.com/#/c/116841/
https://android-review.googlesource.com/#/c/144561/
https://android-review.googlesource.com/#/c/144568/
https://android-review.googlesource.com/#/c/144574/
https://android-review.googlesource.com/#/c/144576/
erratum 843419 https://android-review.googlesource.com/#/c/144580/
https://android-review.googlesource.com/#/c/147414/
Basically we can expect them by prebuilt binaries.
And it’s regarding ld.bfd.

10. Tool chain to build device FW
platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9
erratum 835769 https://android-review.googlesource.com/117420
erratum 843419 https://android-review.googlesource.com/145972
Please note that the option is NOT set as default (but will be enabled on NDK, not on platform build).
(https://android-review.googlesource.com/#/c/145066/1/build/tools/toolchain-patches/gcc/0013-Modify-LINK_SPEC-to-pass-fix-cortex-a53-843419-as-de.patch)
ldflags:= ¥
-Wl --fix-cortex-a53-835769 ¥
-Wl --fix-cortex-a53-843419 ¥

11. Tool chain to build device FW
clang, llvm
erratum 835769 https://android-review.googlesource.com/#/c/111240/ (clang)
https://android-review.googlesource.com/#/c/111230/ (llvm)
erratum 843419 Not available...
Basically platform build is by gcc and then it should be optional.
But NDK supports clang/LLVM. And then without the support,
NDK will not be released...

12. NDK : Native libraries for AArch64
Workaround for 835769 is enabled as default on
NDK10d.
And then what application developers need to do is
to ensure workaround for 843419.
But the supported NDK is not released.

13. JavaScript Engine V8 in Chromium
https://code.google.com/p/chromium/issues/list?
can=1&q=Cortex+53+errata&colspec=ID+Pri+M+Week+ReleaseBlock+Cr+Status+Owner+Summary+
OS+Modified&cells=tiles
https://code.google.com/p/chromium/issues/list?
can=1&q=Cortex+53+erratum&colspec=ID+Pri+M+Week+ReleaseBlock+Cr+Status+Owner+Summar
y+OS+Modified&x=m&y=releaseblock&cells=tiles
But “JavaScriptCore” used in WebKit has already the workaround for 835769 but not for 843419
http://code.metager.de/source/xref/WebKit/Source/JavaScriptCore/offlineasm/arm64.rb
Based on my investigation, there is no workaround solution for the errata as
of now.

14. Summary
● For manufacturers/custom ROM developers
○ Build FW with the workaround enabled toolchain
○ Don’t forget to ensure the binary released SW too.
○ Please keep watching not only AOSP but also
chromium’s V8.
● For application developers
○ Build your native library with workaround enabed
NDK and re-release your app with the library.