linux-kernel - Re: [PATCH v2 00/33] locking/atomic: convert all architectures to ARCH

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Date:   Tue, 29 Jun 2021 00:13:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org,
        will@...nel.org, boqun.feng@...il.com, aou@...s.berkeley.edu,
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Subject: Re: [PATCH v2 00/33] locking/atomic: convert all architectures to
 ARCH_ATOMIC

On Mon, Jun 28, 2021 at 02:22:15PM -0700, Randy Dunlap wrote:
> However, something in arch/arc/ did look suspicious so I decided to
> try an ARC allmodconfig build, where I did see a few errors FYI:
> 
> 
>   CC      drivers/iommu/io-pgtable-arm.o
> In file included from ../include/linux/atomic.h:80,
>                  from ../drivers/iommu/io-pgtable-arm.c:12:
> ../drivers/iommu/io-pgtable-arm.c: In function 'arm_lpae_install_table':
> ../include/linux/atomic-arch-fallback.h:60:32: error: implicit declaration of function 'arch_cmpxchg64'; did you mean 'arch_cmpxchg'? [-Werror=implicit-function-declaration]
>    60 | #define arch_cmpxchg64_relaxed arch_cmpxchg64
>       |                                ^~~~~~~~~~~~~~
> ../include/asm-generic/atomic-instrumented.h:1261:2: note: in expansion of macro 'arch_cmpxchg64_relaxed'
>  1261 |  arch_cmpxchg64_relaxed(__ai_ptr, __VA_ARGS__); \
>       |  ^~~~~~~~~~~~~~~~~~~~~~
> ../drivers/iommu/io-pgtable-arm.c:320:8: note: in expansion of macro 'cmpxchg64_relaxed'
>   320 |  old = cmpxchg64_relaxed(ptep, curr, new);
>       |        ^~~~~~~~~~~~~~~~~

0day also reported something like that. We found that this was a
pre-existing error, and Mark's patches only changed the error, it never
successfully build.

cmpxchg64 is an optional feature for 32bit architectures, one that ARMv7
does provide, and uses, for it's iommu bits. Building the ARM iommu
drivers on ARC seem somewhat daft but is a result of that COMPILE_TEST
config.