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Wed, 21 Apr 2021 08:43:09 +0000 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-118-CrBwdaVmPfOEx9eMOh2cMQ-1; Wed, 21 Apr 2021 09:43:02 +0100 X-MC-Unique: CrBwdaVmPfOEx9eMOh2cMQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Wed, 21 Apr 2021 09:43:01 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.015; Wed, 21 Apr 2021 09:43:01 +0100 From: David Laight To: 'Arnd Bergmann' , Vineet Gupta CC: Matthew Wilcox , "grygorii.strashko@ti.com" , "netdev@vger.kernel.org" , "ilias.apalodimas@linaro.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "mhocko@kernel.org" , "linux-mm@kvack.org" , "mgorman@suse.de" , "brouer@redhat.com" , "mcroce@linux.microsoft.com" , "linux-snps-arc@lists.infradead.org" , "linuxppc-dev@lists.ozlabs.org" , "hch@lst.de" , "linux-arm-kernel@lists.infradead.org" Subject: RE: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Thread-Topic: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Thread-Index: AQHXNir2f1yRrc3ugkWz9MvyD1ZvgKq+pqyQ Date: Wed, 21 Apr 2021 08:43:01 +0000 Message-ID: <5c41d562589b497ca3c1047e0e18b3a1@AcuMS.aculab.com> References: <20210416230724.2519198-1-willy@infradead.org> <20210416230724.2519198-2-willy@infradead.org> <20210417024522.GP2531743@casper.infradead.org> <9f99b0a0-f1c1-f3b0-5f84-3a4bfc711725@synopsys.com> <20210420031029.GI2531743@casper.infradead.org> <8d0fce1c-be7c-1c9b-bf5c-0c531db496ac@synopsys.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210421_014306_504892_2AC6A123 X-CRM114-Status: GOOD ( 12.93 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Arnd Bergmann > Sent: 20 April 2021 22:20 > > On Tue, Apr 20, 2021 at 11:14 PM Vineet Gupta > wrote: > > On 4/20/21 12:07 AM, Arnd Bergmann wrote: > > > > > > > which means that half the 32-bit architectures do this. This may > > > cause more problems when arc and/or microblaze want to support > > > 64-bit kernels and compat mode in the future on their latest hardware, > > > as that means duplicating the x86 specific hacks we have for compat. > > > > > > What is alignof(u64) on 64-bit arc? > > > > $ echo 'int a = __alignof__(long long);' | arc64-linux-gnu-gcc -xc - > > -Wall -S -o - | grep -A1 a: | tail -n 1 | cut -f 3 > > 8 > > Ok, good. That test doesn't prove anything. Try running on x86: $ echo 'int a = __alignof__(long long);' | gcc -xc - -Wall -S -o - -m32 .file "" .globl a .data .align 4 .type a, @object .size a, 4 a: .long 8 .ident "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609" .section .note.GNU-stack,"",@progbits Using '__alignof__(struct {long long x;})' does give the expected 4. __alignof__() returns the preferred alignment, not the enforced alignmnet - go figure. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel