Re: The future of Linux32 builds and tests

On Mon, Oct 12, 2015 at 9:56 AM, Steve Fink <[email protected]> wrote:

> On 10/12/2015 08:21 AM, Ryan VanderMeulen wrote:
>
>> On 10/8/2015 1:01 PM, [email protected] wrote:
>>
>>> We recently disabled Linux32 talos testing on all trees.
>>>
>>> Going forward, the question remains, do we need to run Linux32 tests at
>>> all?  This would reduce the complexity of our configs, as well as
>>> significantly reduce our AWS bill. Do the linux32 test results provide
>>> significant differences from the ones we run on on linux64? I see three
>>> options going forward
>>>
>>> 1) Run linux32 builds and tests periodically
>>> 2) Turn off tests but run the builds and make it a Tier 2 platform
>>> 3) Turn off Linux32 builds + tests entirely
>>>
>>> Your data-driven input is sought,
>>>
>>> cheers,
>>> Kim
>>>
>>> Bugs of note
>>> Disable all 32-bit linux testing
>>> https://bugzilla.mozilla.org/show_bug.cgi?id=1209932
>>> Do we need linux32 talos?
>>> https://bugzilla.mozilla.org/show_bug.cgi?id=1204920
>>> Disable linux32 talos testing and reimage machines for windows testing
>>> https://bugzilla.mozilla.org/show_bug.cgi?id=1208449
>>>
>>>
>> Note that SM(arm) builds run on linux32 build slaves (and AFAIK, they
>> have to). Not sure where SM builds fit in with all of this, but I figured
>> it was at least worth explicitly calling out.
>>
>
> I don't *think* they have to, since they run fine on my local (linux64)
> box. But cross-compilation always confuses me.
>
> When I run it locally, the arm-sim build (aka SM(arm)) uses my 64-bit gcc
> with -m32 to generate a 32-bit JS shell whose JIT generates 32-bit ARM
> code, and then runs it via a 32-bit ARM simulator. (I think that rest of
> the shell would be fine if it were compiled as 64-bit, but the simulator
> part only works when compiled as 32-bit x86 code?)
>

32bit arches use a different Value packing format than 64bit. The JITs
assume at a very low level that Values (and values in general) have the
same layout and alignment requirements everywhere. As Steve noted, however,
cross compilation with -m32 works just fine.


> Like I said, cross-compilation is confusing, especially when you mix in
> JIT and a simulator.
>
> Also note that as of very recently there is an SM(arm64) build, which is
> 64-bit all the way through (including generating ARM64 code). But that does
> not replace the need for the 32-bit ARM simulator. Generally speaking, we
> can't just ditch 32-bit architectures entirely because we need to be able
> to run on 32-bit ARM devices for the foreseeable future.
>
>
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