Improve ARM support

[ompiteam]

Per discussion on the devel list:

http://www.open-mpi.org/community/lists/devel/2013/01/11955.php

Lief would like to revert r27882 and implement it differently (see first mail in this thread). r27882 was not accepted into v1.6; a different (simpler) workaround was used as a stopgap.

Lief -- do you have a timeline for this implementation? Can it be done in the near enough future to include in the v1.7 series? Should be revert r27882 in the immediate future?

[ompiteam]

Imported from trac issue 3481. Created by jsquyres on 2013-01-25T18:57:00, last modified: 2014-04-22T16:01:01

[ompiteam]

Trac comment by phargrov on 2014-01-23 19:38:55:

No progress in 12 months?

The original description indicates that 1.6 used a "different" solution to the ARM asm issues, and asks if r27882 should be reverted (in time for the then-future v1.7). However, the distinct ARMV[567].asm files created in r27882 do not appear in the trunk or v1.7 branch. So, either I am misunderstanding the ticket's Description, or something has changed without an update to the ticket.

I can confirm that the current 1.7.4rc tarballs, configured with no special options, passes "make all install check" on a multi-core armv7 system (Ubuntu Precise on QEMU-emulated Versatile Express).

I also have an armv5 (QEMU-emulated Versatile PB) where I suspect we must fail due to attempts to use strex/ldrex instructions in the asm code (though I've not had time to confirm).

-Paul

[bosilca]

Several issues with compiling on a RasberryPi2 (armv7-a) have been reported on the mailing list. The patch proposed in the original svn r27882 provides an ugly but functional solution. I propose we reintegrate the original patch in master.

[jsquyres]

@bosilca Sounds good. Can you commit to master?

[bosilca]

I just got a rpi2. Give me few days to check the status of this.

[jsquyres]

Move this to the Future milestone -- I think 2.x is the earliest this will happen.

[jsquyres]

@shamisp Just saw this in the old issues -- can you look to see if it is still relevant? If not, feel free to close it. Thanks.

[hppritcha]

Moving to 3.x milestone

[hppritcha]

@shamisp if you want anything for ARM in 3.0.0 needs to be in the pipeline this week. We're planning on forking this week and only what's on #3107 (modulo bug fixes) will get in.

[jsquyres]

I believe that ARMv8 is now well-supported.