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Re: [PATCH 05/19] arm64: rename COMPAT to AARCH32_EL0 in Kconfig
- From: Arnd Bergmann <arnd at arndb dot de>
- To: Catalin Marinas <catalin dot marinas at arm dot com>
- Cc: "Zhangjian (Bamvor)" <bamvor dot zhangjian at huawei dot com>, Yury Norov <ynorov at caviumnetworks dot com>, linux-arm-kernel at lists dot infradead dot org, linux-kernel at vger dot kernel dot org, linux-doc at vger dot kernel dot org, linux-arch at vger dot kernel dot org, libc-alpha at sourceware dot org, schwidefsky at de dot ibm dot com, heiko dot carstens at de dot ibm dot com, pinskia at gmail dot com, broonie at kernel dot org, joseph at codesourcery dot com, christoph dot muellner at theobroma-systems dot com, szabolcs dot nagy at arm dot com, klimov dot linux at gmail dot com, Nathan_Lynch at mentor dot com, agraf at suse dot de, Prasun dot Kapoor at caviumnetworks dot com, kilobyte at angband dot pl, geert at linux-m68k dot org, philipp dot tomsich at theobroma-systems dot com, manuel dot montezelo at gmail dot com, linyongting at huawei dot com, maxim dot kuvyrkov at linaro dot org, davem at davemloft dot net, Andrew Pinski <apinski at cavium dot com>, Andrew Pinski <Andrew dot Pinski at caviumnetworks dot com>, Bamvor Jian Zhang <bamvor dot zhangjian at linaro dot org>, Hanjun Guo <guohanjun at huawei dot com>
- Date: Thu, 11 Aug 2016 22:29:03 +0200
- Subject: Re: [PATCH 05/19] arm64: rename COMPAT to AARCH32_EL0 in Kconfig
- Authentication-results: sourceware.org; auth=none
- References: <1466207668-10549-1-git-send-email-ynorov@caviumnetworks.com> <6457502.FRufylo3sd@wuerfel> <20160811163003.GD18366@e104818-lin.cambridge.arm.com>
On Thursday, August 11, 2016 5:30:03 PM CEST Catalin Marinas wrote:
> > > > and you can have ARM binaries with
> > > > PER_LINUX (using the arm64 uname) just like you can have
> > > > arm64 binaries running with PER_LINUX32.
> > >
> > > I was actually looking to enforce the 32-bit binaries to only see
> > > PER_LINUX32, though with a risk of breaking the ABI. OTOH, people are
> > > abusing this and write 32-bit apps relying on the 64-bit /proc/cpuinfo:
> > >
> > > http://lkml.kernel.org/g/1464706504-25224-3-git-send-email-catalin.marinas@arm.com
> > >
> > > (you were summoned on that discussion couple of times ;))
> >
> > Hmm, I thought I saw the thread and didn't have any good idea for
> > the uname information, but didn't notice it was for /proc/cpuinfo.
> >
> > What's wrong with always showing both the 32-bit and the 64-bit
> > hwcap strings here (minus the duplicates, which hopefully have
> > the same meaning here)?
>
> As I said above, some of them have the same name (which may be a good
> thing at a first look) but we don't have an architecture guarantee that
> the feature is present in both AArch32 and AArch64 modes (e.g. AES may
> only be available in AArch64).
Is this the case on actual implementations that exist today? If they
are actually always both present, we might be able to get away with it.
Arnd