From: Will Deacon <will.deacon@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
kernel-build-reports@lists.linaro.org, olof@lixom.net,
David Miller <davem@davemloft.net>,
eric.dumazet@gmail.com, netdev@vger.kernel.org,
linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: next build: 235 warnings 3 failures (next/next-20151117)
Date: Tue, 17 Nov 2015 16:44:53 +0000 [thread overview]
Message-ID: <20151117164453.GF30101@arm.com> (raw)
In-Reply-To: <4694362.ZPL12j6kR2@wuerfel>
Hi Arnd,
On Tue, Nov 17, 2015 at 09:57:30AM +0100, Arnd Bergmann wrote:
> On Monday 16 November 2015 19:05:05 Olof's autobuilder wrote:
> >
> > Errors:
> >
> > arm64.allmodconfig:
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
>
> The patch below seems to fix it. Please review/apply.
>
> 8<----
> Subject: ARM64: make smp_load_acquire() work with const arguments
>
> smp_load_acquire() uses typeof() to declare a local variable for temporarily
> storing the output of the memory access. This fails when the argument is
> constant, because the assembler complains about using a constant register
> as output:
>
> arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1'
> used as 'asm' output
Do you know the usage in the kernel causing this warning?
> This changes the implementation to use an 'unsigned long' for the temporary value
> and only cast it to the original type in the end.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index 624f9679f4b0..05fa329467f6 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -64,7 +64,7 @@ do { \
>
> #define smp_load_acquire(p) \
> ({ \
> - typeof(*p) ___p1; \
> + unsigned long ___p1; \
> compiletime_assert_atomic_type(*p); \
> switch (sizeof(*p)) { \
> case 1: \
> @@ -84,7 +84,7 @@ do { \
> : "=r" (___p1) : "Q" (*p) : "memory"); \
> break; \
> } \
> - ___p1; \
> + (typeof(*p))___p1; \
My worry about having the cast here is if somebody decides to
smp_load_acquire from a packed 64-bit structure (e.g. some sort of lock),
then we'll get a conversion to non-scalar type error from the compiler.
Will
next prev parent reply other threads:[~2015-11-17 16:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <564a9961.878b420a.331b8.fffffd62@mx.google.com>
2015-11-17 8:57 ` next build: 235 warnings 3 failures (next/next-20151117) Arnd Bergmann
2015-11-17 16:44 ` Will Deacon [this message]
2015-11-17 17:01 ` Eric Dumazet
2015-11-17 17:03 ` Arnd Bergmann
2015-11-17 17:12 ` Will Deacon
2015-11-17 19:17 ` Arnd Bergmann
2015-11-18 10:14 ` Will Deacon
2015-11-18 12:11 ` David Laight
2015-11-18 12:28 ` Will Deacon
2015-11-18 15:21 ` David Laight
2015-11-18 15:36 ` Will Deacon
2015-11-18 15:57 ` David Laight
2015-11-18 10:22 ` David Laight
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