linux-kernel - Re: [PATCH v2 07/12] parisc/percpu: Work around the lack of __SIZEOF_INT128_

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Message-ID: <20230601105021.GU4253@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Jun 2023 12:50:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Helge Deller <deller@....de>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>, dennis@...nel.org,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Heiko Carstens <hca@...ux.ibm.com>, gor@...ux.ibm.com,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        borntraeger@...ux.ibm.com, Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        suravee.suthikulpanit@....com, Robin Murphy <robin.murphy@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, iommu@...ts.linux.dev,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-crypto@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        linux-parisc@...r.kernel.org,
        John David Anglin <dave.anglin@...l.net>,
        Sam James <sam@...too.org>
Subject: Re: [PATCH v2 07/12] parisc/percpu: Work around the lack of
 __SIZEOF_INT128__

On Thu, Jun 01, 2023 at 12:32:38PM +0200, Helge Deller wrote:
> On 6/1/23 12:14, Peter Zijlstra wrote:
> > On Wed, May 31, 2023 at 04:21:22PM +0200, Arnd Bergmann wrote:
> > 
> > > It would be nice to have the hack more localized to parisc
> > > and guarded with a CONFIG_GCC_VERSION check so we can kill
> > > it off in the future, once we drop either gcc-10 or parisc
> > > support.
> > 
> > I vote for dropping parisc -- it's the only 64bit arch that doesn't have
> > sane atomics.
> 
> Of course I'm against dropping parisc.

:-)

> > Anyway, the below seems to work -- build tested with GCC-10.1
> 
> I don't think we need to care about gcc-10 on parisc.
> Debian and Gentoo are the only supported distributions, while Debian
> requires gcc-12 to build > 6.x kernels, and I assume Gentoo uses at least
> gcc-12 as well.
> 
> So raising the gcc limit for parisc only (at least temporarily for now)
> should be fine and your workaround below wouldn't be necessary, right?

Correct, if you're willing to set minimum GCC version to 11 for parisc
all is well and this patch can go play in the bit bucket.