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List:       wine-devel
Subject:    RE: [PATCH 2/2] ntdll: Move InterlockedCompareExchange128 support to winnt.h.
From:       Puetz Kevin A <PuetzKevinA () JohnDeere ! com>
Date:       2020-07-31 17:46:07
Message-ID: DM6PR05MB685856BF3AB878A6452D0650B54E0 () DM6PR05MB6858 ! namprd05 ! prod ! outlook ! com
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> Oh, I see, I didn't know it's already broken on aarch64. FWIW, I just wanted
> to fix a warning on clang msvcrt target and while doing that, I generalized the
> solution. We can wait with that for aarch64 solution.

Though what I was waiting on was to find out whether or was my problem
or somebody else's (i.e. would it still be an issue on our eventual BSP).
Which is, at least a bit, independent of whether wine needs a solution in general.
I probably should have at filed the bug anyway 😊

> Depending on -latomic may be problematic in PE builds. If I read libatomic

Mingw should have a -latomic too, it's the underlying runtime for the C++11 atomics
(but it just contains the C-API out-of-line implementations to fall back on 
when there aren't appropriate intrinsics).

> source right, libatomic resorts to using lock in this case (pthread_mutex_lock
> or equivalent, depending on host). 

Yes, that's what it does, which seemed equivalent to what wine had previously done,
and was easy to drop in as a workaround.

> We could probably just add a variant of affected RtlInterlocked*SList* functions 
> that would use critical section instead of interlocked operations.

Yep. Or do what I think MS actually did, and implement the Header8 layout for when
you can't use double-pointer compare-and-exchange. They need that anyway,
(though maybe not anymore) since original amd64 CPUs don't have cmpxchg16b either.

I don't know the details on SLIST_HEADER::Header8 (presumably the same, just with
fewer bits in some of the fields), and there doesn't seem to be a lot of MSDN \
documentation But here's some references I've dug up that at least mention it existed \
for such cases... And obviously the Header8 struct in wine and reactos came from \
somewhere...

https://docs.microsoft.com/en-us/windows/win32/sync/interlocked-singly-linked-lists
https://devblogs.microsoft.com/oldnewthing/20110819-00/?p=9853
https://docs.microsoft.com/en-us/previous-versions/windows/desktop/legacy/ms683553(v=vs.85)?redirectedfrom=MSDN
 https://cbloomrants.blogspot.com/2010/05/05-29-10-lock-free-in-x64.html

> Thanks,
> 
> Jacek


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