linux-kernel - Re: [PATCH 05/20] arm64: rename COMPAT to AARCH32

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Date:   Mon, 19 Jun 2017 16:58:16 +0100
From:   James Morse <james.morse@....com>
To:     Yury Norov <ynorov@...iumnetworks.com>
CC:     Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Andrew Pinski <pinskia@...il.com>,
        Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
        Adam Borowski <kilobyte@...band.pl>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Steve Ellcey <sellcey@...iumnetworks.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Florian Weimer <fweimer@...hat.com>,
        Bamvor Zhangjian <bamvor.zhangjian@...wei.com>,
        Andreas Schwab <schwab@...e.de>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        schwidefsky@...ibm.com, broonie@...nel.org,
        Joseph Myers <joseph@...esourcery.com>,
        christoph.muellner@...obroma-systems.com, szabolcs.nagy@....com,
        klimov.linux@...il.com, Nathan_Lynch@...tor.com, agraf@...e.de,
        Prasun.Kapoor@...iumnetworks.com, geert@...ux-m68k.org,
        philipp.tomsich@...obroma-systems.com, manuel.montezelo@...il.com,
        linyongting@...wei.com, davem@...emloft.net,
        zhouchengming1@...wei.com, Andrew Pinski <apinski@...ium.com>,
        Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>
Subject: Re: [PATCH 05/20] arm64: rename COMPAT to AARCH32_EL0 in Kconfig

Hi Yury,

On 04/06/17 12:59, Yury Norov wrote:
> From: Andrew Pinski <apinski@...ium.com>
> 
> In this patchset  ILP32 ABI support is added. Additionally to AARCH32,
> which is binary-compatible with ARM, ILP32 is (mostly) ABI-compatible.
> 
> From now, AARCH32_EL0 (former COMPAT) config option means the support of
> AARCH32 userspace, ARM64_ILP32 - support of ILP32 ABI (see next patches),
> and COMPAT indicates that one of them, or both, is enabled.
> 
> Where needed, CONFIG_COMPAT is changed over to use CONFIG_AARCH32_EL0 instead

Nit: You have 'COMPAT' around compat_hwcap_str's definition, but its only user
is wrapped in 'AARCH32_EL0'.


After this patch
arch/arm64/kernel/perf_callchain.c::perf_callchain_user() still has:
>	if (!compat_user_mode(regs)) {
>		/* AARCH64 mode */
...
>	} else {
> #ifdef CONFIG_COMPAT
> 		/* AARCH32 compat mode */
...
> #endif
>	}

I think this one should become CONFIG_AARCH32_EL0. compat to this code means the
fp is 'compat_fp' in x11, and it should read a 32bit call chain from user-space.

This is confusing as 'is_compat_task()' matches one of aarch32 or ilp32, but
compat_user_mode(regs) only matches aarch32 as it checks the saved spsr. I can't
see any problem caused by this today, but its going to bite someone in the
future. Can this be renamed aarch32_user_mode()? (turns out 'a32' is the name of
just one of aarch32's instruction sets[0].)


Thanks,

James

[0] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka16137.html