branches: 1.5.50;
allow inclusion of atomic ops in librump

Allow atomic ops to be built as part of libpthread.

Only build atomic ops for libkern/libc.

branches: 1.2.4;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file Makefile.inc was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_add.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_and.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.5.62;
enable profiling of assembly functions.

branches: 1.4.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.3.4;
Add atomic_cas_foo_ni().

branches: 1.2.4;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_cas.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_dec.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_inc.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.3.64;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_op_asm.h was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_or.S was initially added on branch thorpej-atomic.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.4.62;
enable profiling of assembly functions.

branches: 1.3.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.2.4; 1.2.8;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file atomic_swap.S was initially added on branch thorpej-atomic.

Introduce membar_acquire/release. Deprecate membar_enter/exit.

The names membar_enter/exit were unclear, and the documentation of
membar_enter has disagreed with the implementations on sparc,
powerpc, and even x86(!) for the entire time it has been in NetBSD.

The terms `acquire' and `release' are ubiquitous in the literature
today, and have been adopted in the C and C++ standards to mean
load-before-load/store and load/store-before-store, respectively,
which are exactly the orderings required by acquiring and releasing a
mutex, as well as other useful applications like decrementing a
reference count and then freeing the underlying object if it went to
zero.

Originally I proposed changing one word in the documentation for
membar_enter to make it load-before-load/store instead of
store-before-load/store, i.e., to make it an acquire barrier. I
proposed this on the grounds that

(a) all implementations guarantee load-before-load/store,
(b) some implementations fail to guarantee store-before-load/store,
and
(c) all uses in-tree assume load-before-load/store.

I verified parts (a) and (b) (except, for (a), powerpc didn't even
guarantee load-before-load/store -- isync isn't necessarily enough;
need lwsync in general -- but it _almost_ did, and it certainly didn't
guarantee store-before-load/store).

Part (c) might not be correct, however: under the mistaken assumption
that atomic-r/m/w then membar-w/rw is equivalent to atomic-r/m/w then
membar-r/rw, I only audited the cases of membar_enter that _aren't_
immediately after an atomic-r/m/w. All of those cases assume
load-before-load/store. But my assumption was wrong -- there are
cases of atomic-r/m/w then membar-w/rw that would be broken by
changing to atomic-r/m/w then membar-r/rw:

https://mail-index.netbsd.org/tech-kern/2022/03/29/msg028044.html

Furthermore, the name membar_enter has been adopted in other places
like OpenBSD where it actually does follow the documentation and
guarantee store-before-load/store, even if that order is not useful.
So the name membar_enter currently lives in a bad place where it
means either of two things -- r/rw or w/rw.

With this change, we deprecate membar_enter/exit, introduce
membar_acquire/release as better names for the useful pair (r/rw and
rw/w), and make sure the implementation of membar_enter guarantees
both what was documented _and_ what was implemented, making it an
alias for membar_sync.

While here, rework all of the membar_* definitions and aliases. The
new logic follows a rule to make it easier to audit:

membar_X is defined as an alias for membar_Y iff membar_X is
guaranteed by membar_Y.

The `no stronger than' relation is (the transitive closure of):

- membar_consumer (r/r) is guaranteed by membar_acquire (r/rw)
- membar_producer (w/w) is guaranteed by membar_release (rw/w)
- membar_acquire (r/rw) is guaranteed by membar_sync (rw/rw)
- membar_release (rw/w) is guaranteed by membar_sync (rw/rw)

And, for the deprecated membars:

- membar_enter (whether r/rw, w/rw, or rw/rw) is guaranteed by
membar_sync (rw/rw)
- membar_exit (rw/w) is guaranteed by membar_release (rw/w)

(membar_exit is identical to membar_release, but the name is
deprecated.)

Finally, while here, annotate some of the instructions with their
semantics. For powerpc, leave an essay with citations on the
unfortunate but -- as far as I can tell -- necessary decision to use
lwsync, not isync, for membar_acquire and membar_consumer.

Also add membar(3) and atomic(3) man page links.

Nix trailing whitespace in files of membars, atomics, and lock stubs.

Will be touching many of these files soon for functional changes.

No functional change intended.

branches: 1.7.16;
Introduce membar_datadep_consumer.

Discussed briefly on tech-kern without objection:

https://mail-index.netbsd.org/tech-kern/2014/11/20/msg018054.html
https://mail-index.netbsd.org/tech-kern/2015/01/07/msg018326.html

branches: 1.6.40;
enable profiling of assembly functions.

branches: 1.5.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.4.4;
Always enable memory barriers in userspace, otherwise libpthread won't
work correctly on MP systems.

Fix pthread problem. (export membar* to userland)

branches: 1.2.4;
Pull in alpha atomic ops from the thorpej-atomic branch.

branches: 1.1.2;
file membar_ops.S was initially added on branch thorpej-atomic.