Boost C++ Libraries: Ticket #5331: usage of deprecated swp instruction on arm

Peter Dimov — Wed, 23 Mar 2011 00:04:08 GMT

I'm pretty sure that it can be fixed in principle using ldrex/strex; not only that, but it should be possible to implement sp_counted_base for armv6 using these, without resorting to a spinlock. However, I have neither the necessary experience with ARM assembly nor the resources to test the code.

abel@… — Thu, 19 Jan 2012 10:12:53 GMT

Hi,

I'm not sure if this is still on the agenda or not. However, I had to fix this specific problem earlier this year. I followed the outline given at http://www.boost.org/support/bugs.html to produce the attached patch against the latest trunk.

The patch should take care of deprecation warnings.

The latest trunk introduced a memory barrier after the swp instructiopn. However, I think using a memory barrier is only ever necessary when the lock was actually acquired. Yet, the trunk codebase sets one up on each call of try_lock()... This might have some performance implications.

As of right now, try_lock() is called in lock() inside a loop which explicitly yields the thread if try_lock() failed. It might be better to have that loop in try_lock() instead and only do a dmb if the lock was acquired. However, this might change the API in more ways than most people would be comfortable with, I guess...

attachment set

abel@… — Thu, 19 Jan 2012 10:14:05 GMT

attachment → arm_spinlock_fix.patch

Proposed patch for strex and ldrex usage on AMR 6 and ARM7.

attachment set

abel@… — Thu, 19 Jan 2012 10:22:03 GMT

attachment → arm_spinlock_fix.2.patch

[Fixed] Proposed patch for strex and ldrex usage on AMR 6 and ARM7.

abel@… — Thu, 19 Jan 2012 10:22:37 GMT

Argh, sorry, forgot a semicolon while pasting my fix in there...

version changed

abel@… — Fri, 09 Mar 2012 14:32:38 GMT

version Boost 1.46.0 → Boost 1.50.0

bump

Peter Dimov — Mon, 12 Mar 2012 17:31:24 GMT

(In [77315]) Apply patch from #5331. Refs #5331.

status changed; resolution set

Peter Dimov — Mon, 12 Mar 2012 17:37:54 GMT

status new → closed
resolution → fixed

(In [77317]) Merge [77315] to release. Closes #5331.