From: Ash Wilding <ash.j.wilding@gmail.com>
To: jbeulich@suse.com
Cc: ash.j.wilding@gmail.com, bertrand.marquis@arm.com,
julien@xen.org, rahul.singh@arm.com,
xen-devel@lists.xenproject.org
Subject: Re: [RFC PATCH v2 05/15] xen/arm: pull in Linux atomics helpers and dependencies
Date: Thu, 12 Nov 2020 10:52:20 +0000 [thread overview]
Message-ID: <20201112105220.22799-1-ash.j.wilding@gmail.com> (raw)
In-Reply-To: <e5603684-1f4b-83f3-8b80-6c9d045912cc@suse.com>
Hey Jan,
>>
>> Note that Linux's arm32 atomics helpers use the READ_ONCE() and
>> WRITE_ONCE() macros defined in <asm-generic/rwonce.h>, while Linux's
>> arm64 atomics helpers use __READ_ONCE() and __WRITE_ONCE().
>
> And our ACCESS_ONCE() can't be used, or be made usable? I don't think
> we want a 3rd variant when we're already in the process of discussing
> how to fold the two ones we have right now.
Many thanks for the pointer, I'm still familiarising myself with Xen's
codebase and wasn't aware of ACCESS_ONCE(); yes, that's exactly what we
need which means we can drop Linux's <asm-generic/rwonce.h> completely.
That also means:
>
> I don't think weakening the checking is a good idea when the macros
> are being made available for general use. If they'd be renamed to be
> private flavors for use just in Arm's atomics, this would be a
> different thing.
This problem goes away, as does the need/desire to bump the minimum GCC
version up to 4.9 for xen/arm just to support the usage of C11 _Generic
in Linux's <linux/compiler_types.h>.
That said, agreed, I did think the way I'd done it was a tad suspect
hence the "possibly contentious" disclaimer :-) I'll keep this in mind
for similar porting work in future.
>>
>> \ No newline at end of file
>
> This wants taking care of in any event - there are multiple instances
> in this patch (in fact it looks as if all of the new files had this
> issue), and I didn't check others.
Ack, will fix.
Thanks for taking the time to provide feedback!
Cheers,
Ash.
next prev parent reply other threads:[~2020-11-12 10:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-11 21:51 [RFC PATCH v2 00/15] xen/arm: port Linux LL/SC and LSE atomics helpers to Xen Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 01/15] xen/arm: Support detection of CPU features in other ID registers Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 02/15] xen/arm: Add detection of Armv8.1-LSE atomic instructions Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 03/15] xen/arm: Add ARM64_HAS_LSE_ATOMICS hwcap Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 04/15] xen/arm: Delete Xen atomics helpers Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 05/15] xen/arm: pull in Linux atomics helpers and dependencies Ash Wilding
2020-11-12 8:31 ` Jan Beulich
2020-11-12 10:52 ` Ash Wilding [this message]
2020-11-11 21:51 ` [RFC PATCH v2 06/15] xen: port Linux <asm-generic/rwonce.h> to Xen Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 07/15] xen/arm: prepare existing Xen headers for Linux atomics Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 08/15] xen/arm64: port Linux's arm64 atomic_ll_sc.h to Xen Ash Wilding
2020-12-15 18:38 ` Julien Grall
2020-11-11 21:51 ` [RFC PATCH v2 09/15] xen/arm64: port Linux's arm64 atomic_lse.h " Ash Wilding
2020-11-11 21:51 ` [RFC PATCH v2 10/15] xen/arm64: port Linux's arm64 cmpxchg.h " Ash Wilding
2020-12-15 18:53 ` Julien Grall
2020-11-11 21:51 ` [RFC PATCH v2 11/15] xen/arm64: port Linux's arm64 atomic.h " Ash Wilding
2020-11-11 21:52 ` [RFC PATCH v2 12/15] xen/arm64: port Linux's arm64 lse.h " Ash Wilding
2020-11-11 21:52 ` [RFC PATCH v2 13/15] xen/arm32: port Linux's arm32 atomic.h " Ash Wilding
2020-11-11 21:52 ` [RFC PATCH v2 14/15] xen/arm32: port Linux's arm32 cmpxchg.h " Ash Wilding
2020-11-11 21:52 ` [RFC PATCH v2 15/15] xen/arm: remove dependency on gcc built-in __sync_fetch_and_add() Ash Wilding
2020-12-15 19:31 ` [RFC PATCH v2 00/15] xen/arm: port Linux LL/SC and LSE atomics helpers to Xen Julien Grall
2020-12-17 15:37 ` Ash Wilding
2020-12-18 12:17 ` Ash Wilding
2021-02-14 18:36 ` Julien Grall
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