Re: lib/53051: __atomic_is_lock_free missing on NetBSD/sparc

[Jason Thorpe <thorpej%me.com@localhost>]

> On Dec 22, 2018, at 9:55 AM, coypu%sdf.org@localhost wrote:
> 
> The following reply was made to PR lib/53051; it has been noted by GNATS.
> 
> From: coypu%sdf.org@localhost
> To: gnats-bugs%NetBSD.org@localhost
> Cc: 
> Subject: Re: lib/53051: __atomic_is_lock_free missing on NetBSD/sparc
> Date: Sat, 22 Dec 2018 17:51:13 +0000
> 
> Worth noting that netbsd *does* have locked atomics for SPARC.
> They are in src/common/lib/libc/arch/sparc/atomic

So, the way I understand this is that, on the "sparc" architecture, this would return true on a uniprocessor system and false on a multiprocessor system.  This is because on a multiprocessor system, our atomics always use an interlock table because sparc only has LDSTUB (and all of the various operations are implemented on top of the interlocked compare-and-swap primitive), whereas on a uniprocessor, it's implemented using a restartable atomic sequence.

That, however, assumes that all of the C11 atomic calls get vectored through our libc implementation (which is based on the Solaris atomics API) ... all bets are off if they end up using some random implementation in libgcc.

-- thorpej