arm: record_sp_limit is assuming arm > ARM7

[pnkfelix]

In my attempts to run a hello world targetting my ARM chromebook, I am getting an illegal instruction from the first instruction of record_sp_limit:

https://github.com/mozilla/rust/blob/9c39992021477740673a5b4982014678743c7fdf/src/rt/arch/arm/record_sp.S#L18

The problem, AFAICT, is that mrc p15, #0, r3, c13, c0, #3 is too new of an instruction to use on this platform (armv7l GNU/Linux, Arch distribution).

At least, that's my interpretation of the summary provided by the netbsd folks here:
http://mail-index.netbsd.org/port-arm/2012/02/14/msg001303.html

Commenting out the mrc lines in record_sp_limit and get_sp_limit seem to get the test a bit further (so that it crashes in pthread_mutex_lock instead...

[luqmana]

That odd since I've been able to successfully run on an ARMv5TEJ board.

[pnkfelix]

oh wait, I may have misinterpreted that note from the NetBSD folks: they said its not supported on ARM7, but that's not the same as ARMv7.

[luqmana]

Also, I remember someone running into this with their Beagle Bone running Debian and I think they eventually got it working by upgrading to a newer kernel.

[flaper87]

@pnkfelix I don't have a way to verify this. Is this still an issue? Have you tested this lately?

[pnkfelix]

No but I'll try to do another build on my Chromebook this weekend. (assigning to self as reminder to investigate further.)

[steveklabnik]

Given that you un-assigned yourself, @pnkfelix , I'm going to assume things are okay here, or at least, not reproducible. If anyone else is seeing this, please let me know and we'll re-open, thanks!