From owner-freebsd-amd64@freebsd.org  Wed Aug  1 07:57:16 2018
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Date: Wed, 1 Aug 2018 10:57:04 +0300
From: Konstantin Belousov <kib@freebsd.org>
To: Mark Millard <marklmi@yahoo.com>
Cc: mmacy@FreeBSD.org, svn-src-head@freebsd.org, freebsd-hackers@freebsd.org, 
 freebsd-amd64@freebsd.org
Subject: Re: svn commit: r335873 - in head: . sys/amd64/amd64
 sys/amd64/include  sys/conf sys/i386/i386 sys/i386/include sys/sys sys/vm
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On Tue, Jul 31, 2018 at 06:46:31PM -0700, Mark Millard via freebsd-amd64 wrote:
> > Author: mmacy
> > Date: Mon Jul  2 19:48:38 2018
> > New Revision: 335873
> > URL: 
> > https://svnweb.freebsd.org/changeset/base/335873
> > 
> > 
> > Log:
> >   inline atomics and allow tied modules to inline locks
> >   
> >   - inline atomics in modules on i386 and amd64 (they were always
> >     inline on other arches)
> >   - allow modules to opt in to inlining locks by specifying
> >     MODULE_TIED=1 in the makefile
> 
> I recently found the following about ABI incompatibilities
> between clang and gcc relative to C11 language based
> atomics:
> 
> https://bugs.llvm.org/show_bug.cgi?id=26462
> 
> 26462 ??? GCC/clang C11 _Atomic incompatibility
> 
> 
> So are there implications about building the kernel
> vs. modules that overall mix the toolchains once
> modules are loaded? Do the toolchains need to match,
> at least for amd64 and i386 TARGET_ARCH 's?
This is irrelevant since kernel does not use C11 atomics, we roll
our own version, which tries to follow C11 model.

Lack of the ABI for atomics is one of the reason to not use compiler
C11 atomics in kernel and C runtime.