Discontinuation of V8 support for ARM chips without VFPv2

[Daniel Clifford]

Due the increasing cost of the keeping the "no-VFPv2" port of V8 working on ARM, we are planning on making 3.17 the last V8 release that that supports ARM chips without VFPv2. Starting with the 3.18 release, the minimal V8 requirements will increase to ARMv6 + VFPv2. In order to simplify maintenance, we will also remove the "pre-VFP2" ARM code from the V8 code base.

Danno

[Tom Jacobs]

Hi Danno,

We're running V8 on Android and we're finding that it's crashing on some older Android devices (a few years old), we suspect those that don't have VFPv2.

I see support for no-VFPv2 was removed in 3.18 in this commit: https://code.google.com/p/v8/source/detail?r=14159

Is there any way of bringing no-VFPv2 support back to V8? We're running a fork of it from about 6 months ago (https://github.com/Expensify/jv8), and so might it be as simple as just reverting that commit?

Or is there any other way of working around and having it run fine on those chips?

Our crash happens here:

Trying to load lib /data/data/org.me.mobiexpensifyg/lib/libjv8.so 0x46030c28

... crash ...

#00  pc 0023c978  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

By analyzing which line of code the crash comes from, this is what I get:

$ addr2line -C -f -e obj/local/armeabi/libjv8.so 0023c978

v8::internal::Isolate::EnsureDefaultIsolate()

Thanks,

Tom.

[Rodolph Perfetta]

Hi Tom,

Can you confirm this is a VFP issue:

 * adb shell cat /proc/cpuinfo on the device will tell you if you have VFP

 * what instruction is generating the fault?

On a side note reverting the commit on a post 3.18 V8 will not work.

Cheers,

Rodolph.

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[Daniel Clifford]

Hi Tom,

Unfortunately, it's not possible to just revert the removal of no-VFP. We now require a subset of the Crankshaft compiler for all platforms that we support, and supporting no-VFP Crankshaft code was simply too much work for the value added (Chrome for Android is not support on any of those devices) and maintaining the no-VFP code slowed our progress on the core supported platforms.

I don't think that we even would want to bring no-VFP back to trunk V8, even if you were to magically provide full no-VFP support including Crankshaft based on bleeding edge in a patch for us. The complexity the port adds still outweighs the benefit going forward. If your crash is indeed due to missing VFP support, you will have to use an older version of V8 for those devices.

Regards,

Danno 

[Tom Jacobs]

We've heard reports of our app not working on these phones (usually android 2.2 phones):

- HTC Wildfire S

- Samsung Galaxy Ace

- Samsung Galaxy Mini

- Samsung Galaxy Ace Duos S6802 

- Samsung GT I5510M 

Running the app in a 2.2 armeabi Android simulator, it crashes, and that simulator gives this cpuinfo:

 

/Applications/android-sdk-mac_x86/platform-tools/adb  shell cat /proc/cpuinfo

Processor       : ARM926EJ-S rev 5 (v5l)

BogoMIPS        : 262.14

Features        : swp half thumb fastmult vfp edsp java 

CPU implementer : 0x41

CPU architecture: 5TEJ

CPU variant     : 0x0

CPU part        : 0x926

CPU revision    : 5

Hardware        : Goldfish

Revision        : 0000

Serial          : 0000000000000000

So is the solution just to bring our v8 back to 3.17?

Can you think of any other workaround to get v8 to run on these phones, perhaps by doing floating point some other way?

We also have the option of using Rhino instead for these phones, but we'd have to detect the CPU type first. We may have to go this route.

The crash stack for it is below:

10-31 21:31:54.430      385-385/org.me.mobiexpensifyg D/dalvikvm﹕ Trying to load lib /data/data/org.me.mobiexpensifyg/lib/libjv8.so 0x46030c28

10-31 21:31:54.572        30-30/? I/DEBUG﹕ *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***

10-31 21:31:54.572        30-30/? I/DEBUG﹕ Build fingerprint: 'generic/sdk/generic/:2.2/FRF91/43546:eng/test-keys'

10-31 21:31:54.572        30-30/? I/DEBUG﹕ pid: 385, tid: 385  >>> org.me.mobiexpensifyg <<<

10-31 21:31:54.572        30-30/? I/DEBUG﹕ signal 4 (SIGILL), fault addr 8123b770

10-31 21:31:54.572        30-30/? I/DEBUG﹕ r0 00149a38  r1 00000000  r2 00000000  r3 fffff4f4

10-31 21:31:54.572        30-30/? I/DEBUG﹕ r4 001375d0  r5 8147ddb8  r6 81481e20  r7 81481e38

10-31 21:31:54.581        30-30/? I/DEBUG﹕ r8 00149a38  r9 0000ccb0  10 4208bca4  fp 00000000

10-31 21:31:54.581        30-30/? I/DEBUG﹕ ip 00149a30  sp be984738  lr 8123b76c  pc 8123b770  cpsr 20000010

10-31 21:31:54.741        30-30/? I/DEBUG﹕ #00  pc 0023b770  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

10-31 21:31:54.741        30-30/? I/DEBUG﹕ #01  lr 8123b76c  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

10-31 21:31:54.741        30-30/? I/DEBUG﹕ code around pc:

10-31 21:31:54.741        30-30/? I/DEBUG﹕ 8123b750 e59f305c e7953003 e5830000 e3a00004

10-31 21:31:54.741        30-30/? I/DEBUG﹕ 8123b760 ebfc86ab e1a08000 ebfffdc7 e59f3044

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b770 e3050760 e7953003 e5838000 ebfc86a4

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b780 e1a05000 ebfffe8e e5865000 eaffffdd

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b790 e5970000 e5961000 eb05e6f8 eaffffdd

10-31 21:31:54.751        30-30/? I/DEBUG﹕ code around lr:

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b74c eb05e645 e59f305c e7953003 e5830000

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b75c e3a00004 ebfc86ab e1a08000 ebfffdc7

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b76c e59f3044 e3050760 e7953003 e5838000

10-31 21:31:54.751        30-30/? I/DEBUG﹕ 8123b77c ebfc86a4 e1a05000 ebfffe8e e5865000

10-31 21:31:54.761        30-30/? I/DEBUG﹕ 8123b78c eaffffdd e5970000 e5961000 eb05e6f8

10-31 21:31:54.761        30-30/? I/DEBUG﹕ stack:

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be9846f8  00000000

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be9846fc  be98472c  [stack]

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be984700  00000000

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be984704  0000ccb0  [heap]

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be984708  4208bca4

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be98470c  00000004

10-31 21:31:54.761        30-30/? I/DEBUG﹕ be984710  8147ddb8  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984714  81481e20

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984718  81481e38

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be98471c  afd0cd65  /system/lib/libc.so

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984720  00000004

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984724  8099eac4  /data/data/org.me.mobiexpensifyg/lib/libgnustl_shared.so

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984728  001375d0  [heap]

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be98472c  8147ddb8  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984730  df002777

10-31 21:31:54.771        30-30/? I/DEBUG﹕ be984734  e3a070ad

10-31 21:31:54.771        30-30/? I/DEBUG﹕ #00 be984738  8147c58c  /data/data/org.me.mobiexpensifyg/lib/libjv8.so

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be98473c  00000003

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984740  00000004

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984744  00000000

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984748  80813b00  /system/lib/libdvm.so

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be98474c  b0001169  /system/bin/linker

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984750  b0010488

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984754  00002730

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984758  b0010494

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be98475c  b000122b  /system/bin/linker

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984760  b00134dc

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984764  80900000  /data/data/org.me.mobiexpensifyg/lib/libgnustl_shared.so

10-31 21:31:54.780        30-30/? I/DEBUG﹕ be984768  0000001d

10-31 21:31:54.791        30-30/? I/DEBUG﹕ be98476c  b00103a4

10-31 21:31:54.791        30-30/? I/DEBUG﹕ be984770  b00103a4

10-31 21:31:54.791        30-30/? I/DEBUG﹕ be984774  00002730

10-31 21:31:54.791        30-30/? I/DEBUG﹕ be984778  00002730

10-31 21:31:54.791        30-30/? I/DEBUG﹕ be98477c  b0002817  /system/bin/linker

10-31 21:31:55.641        32-32/? D/Zygote﹕ Process 385 terminated by signal (4)

10-31 21:31:55.651       96-247/system_process I/ActivityManager﹕ Process org.me.mobiexpensifyg (pid 385) has died.

Thanks,

Tom

www.expensify.com

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[Rodolph Perfetta]

Tom,

Yes ARM926 CPU are not supported, not only they don't have VFP but they are ARMv5 when V8 base requirement is ARMv6. So V8 3.17 is the only way for you.

Also I couldn't help noticing your simulator has VFP support (though the real hardware won't). Your crash is not VFP related, you are failing on a movw instruction which is an ARMv7 only instruction when your CPU is ARMv5. So you probably compiled your binary for ARMv7. Compiling for ARMv5 will only move the issue as V8 will emit instruction from newer architecture.

HTH,

Rodolph.