701708 - Rebuild NDK armv6 STLport as arm instead of thumb on build machines

Status: RESOLVED WONTFIX

(Infrastructure & Operations Graveyard :: CIDuty, task, P3)

Description

[(not currently active) Ted Mielczarek]

If we target armv6, currently we have to build --with-thumb=no because a bunch of our code doesn't build in an armv6+thumb configuration. Unfortunately, this causes us to crash on startup, because STLport is built with thumb, and the mismatch is somehow fatal. Rebuilding STLport as arm-only makes this issue go away.

We either need to:
a) Rebuild the STLport in the NDK we're using to be arm-only
b) Fix our code to compile with armv6+thumb
c) Figure out why this mismatch crashes and work around it in some other way

a) is the only one I've tested successfully so far.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Is there any confusion here between thumb and thumb2?  I was under the impression that our thumb build option was sometimes labeled as "thumb" and sometimes as "thumb2", but really represented thumb2 throughout.  Thumb and thumb2 are different instruction sets.

Comment 2

[(not currently active) Ted Mielczarek]

The --with-thumb argument just controls passing "-mthumb" to the compiler. glandium says that GCC will select thumb or thumb2 as appropriate depending on the -march. I think our codebase assumes thumb2 in a few places, which is why we break when building with armv6+thumb.

Comment 3

[Marco Castelluccio [:marco]]

I think thumb code in ARMv6 is really slow. Probably 'a' is the best solution. Or maybe we should try all the solutions and see which one is better in terms of performance.

Comment 4

[(not currently active) Ted Mielczarek]

If someone wants to do the investigation, feel free. I've done a) and know it works, so I'm going to proceed with that solution since it's a lot less work than the others.

I'm going to move this to Release Engineering to get a fixed STLport.

The steps we need to do on the build machines (that produce our android builds) are:
1) Apply a patch to the NDK build scripts for STLport (to be provided shortly)
2) Rebuild STLport in the NDK (this can be done on just one machine and copied to the others)
3) Push the new bits out to all build slaves

Comment 5

[(not currently active) Ted Mielczarek]

Attachment: Build NDK STLport armv6 as arm, not thumb

You'll need to apply this patch to the NDK, then run build/tools/build-stlport.sh. That will produce new binaries in the right places.

Comment 6

[(not currently active) Ted Mielczarek]

I think we're going to skip this and go with the solution Mike came up with in bug 734050 instead.