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Date: Fri, 8 Feb 2019 09:00:07 -0700
From: Nathan Chancellor <natechancellor@...il.com>
To: Julien Thierry <julien.thierry@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
daniel.thompson@...aro.org, joel@...lfernandes.org,
marc.zyngier@....com, christoffer.dall@....com,
james.morse@....com, catalin.marinas@....com, will.deacon@....com,
mark.rutland@....com, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Oleg Nesterov <oleg@...hat.com>,
Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v10 12/25] arm64: irqflags: Use ICC_PMR_EL1 for interrupt
masking
On Fri, Feb 08, 2019 at 09:36:48AM +0000, Julien Thierry wrote:
> Hi Nathan,
>
> On 08/02/2019 04:35, Nathan Chancellor wrote:
> > On Thu, Jan 31, 2019 at 02:58:50PM +0000, Julien Thierry wrote:
>
> [...]
>
> >
> > Hi Julien,
> >
> > This patch introduced a slew of Clang warnings:
> >
> > In file included from arch/arm64/kernel/signal.c:21:
> > In file included from include/linux/compat.h:10:
> > In file included from include/linux/time.h:6:
> > In file included from include/linux/seqlock.h:36:
> > In file included from include/linux/spinlock.h:54:
> > In file included from include/linux/irqflags.h:16:
> > arch/arm64/include/asm/irqflags.h:50:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
> > : "r" (GIC_PRIO_IRQON)
> > ^
> > arch/arm64/include/asm/ptrace.h:39:25: note: expanded from macro 'GIC_PRIO_IRQON'
> > #define GIC_PRIO_IRQON 0xf0
> > ^
> > arch/arm64/include/asm/irqflags.h:46:44: note: use constraint modifier "w"
> > "msr_s " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
> > ^~
> > %w0
>
> I'm not sure I get the relevance of this kind of warnings from Clang.
> Had it been an output operand I could understand the concern of having a
> variable too small to store the register value. But here it's an input
> operand being place in a wider register...
>
> > arch/arm64/include/asm/alternative.h:286:29: note: expanded from macro 'ALTERNATIVE'
> > _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
> > ^
> > arch/arm64/include/asm/alternative.h:88:30: note: expanded from macro '_ALTERNATIVE_CFG'
> > __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
> > ^
> > arch/arm64/include/asm/alternative.h:76:2: note: expanded from macro '__ALTERNATIVE_CFG'
> > newinstr "\n" \
> > ^
> > In file included from arch/arm64/kernel/signal.c:21:
> > In file included from include/linux/compat.h:10:
> > In file included from include/linux/time.h:6:
> > In file included from include/linux/seqlock.h:36:
> > In file included from include/linux/spinlock.h:54:
> > In file included from include/linux/irqflags.h:16:
> > arch/arm64/include/asm/irqflags.h:61:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
> > : "r" (GIC_PRIO_IRQOFF)
> > ^
> > arch/arm64/include/asm/ptrace.h:40:26: note: expanded from macro 'GIC_PRIO_IRQOFF'
> > #define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
> > ^
> > arch/arm64/include/asm/irqflags.h:58:45: note: use constraint modifier "w"
> > "msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0",
> > ^
> > arch/arm64/include/asm/irqflags.h:94:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
> > : "r" (GIC_PRIO_IRQOFF)
> > ^
> > arch/arm64/include/asm/ptrace.h:40:26: note: expanded from macro 'GIC_PRIO_IRQOFF'
> > #define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
> > ^
> > arch/arm64/include/asm/irqflags.h:91:18: note: use constraint modifier "w"
> > "csel %0, %0, %2, eq",
> > ^~
> > %w2
> > arch/arm64/include/asm/alternative.h:286:29: note: expanded from macro 'ALTERNATIVE'
> > _ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
> > ^
> > arch/arm64/include/asm/alternative.h:88:30: note: expanded from macro '_ALTERNATIVE_CFG'
> > __ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
> > ^
> > arch/arm64/include/asm/alternative.h:76:2: note: expanded from macro '__ALTERNATIVE_CFG'
> > newinstr "\n" \
> > ^
> > 3 warnings generated.
> >
> >
> > I am not sure if they should be fixed with Clang's suggestion of a
> > constraint modifier or a cast like commit 1b57ec8c7527 ("arm64: io:
> > Ensure value passed to __iormb() is held in a 64-bit register"), hence
> > this message.
> >
>
> Clang's suggestion would not work as MSR instructions do not operate on
> 32-bit general purpose registers. Seeing that PMR is a 32-bit register,
> I'd avoid adding UL for the GIC_PRIO_IRQ* constants.
>
> So I'd recommend just casting the the asm inline operands to unsigned
> long. This should only affect the 3 locations
> arch/arm64/include/asm/irqflags.h.
>
> Does the following patch work for you?
Hi Julien,
Yes it does, thank you for the quick response and fix!
Nathan
>
> Thanks,
>
> --
> Julien Thierry
>
>
> -->
>
> From e839dec632bbf440efe8314751138ba46324078c Mon Sep 17 00:00:00 2001
> From: Julien Thierry <julien.thierry@....com>
> Date: Fri, 8 Feb 2019 09:21:58 +0000
> Subject: [PATCH] arm64: irqflags: Fix clang build warnings
>
> Clang complains when passing asm operands that are smaller than the
> registers they are mapped to:
>
> arch/arm64/include/asm/irqflags.h:50:10: warning: value size does not
> match register size specified by the constraint and modifier
> [-Wasm-operand-widths]
> : "r" (GIC_PRIO_IRQON)
>
> Fix it by casting the affected input operands to a type of the correct
> size.
>
> Reported-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Julien Thierry <julien.thierry@....com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> arch/arm64/include/asm/irqflags.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index d4597b2..43d8366 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -47,7 +47,7 @@ static inline void arch_local_irq_enable(void)
> "dsb sy",
> ARM64_HAS_IRQ_PRIO_MASKING)
> :
> - : "r" (GIC_PRIO_IRQON)
> + : "r" ((unsigned long) GIC_PRIO_IRQON)
> : "memory");
> }
>
> @@ -58,7 +58,7 @@ static inline void arch_local_irq_disable(void)
> "msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0",
> ARM64_HAS_IRQ_PRIO_MASKING)
> :
> - : "r" (GIC_PRIO_IRQOFF)
> + : "r" ((unsigned long) GIC_PRIO_IRQOFF)
> : "memory");
> }
>
> @@ -91,7 +91,7 @@ static inline unsigned long arch_local_save_flags(void)
> "csel %0, %0, %2, eq",
> ARM64_HAS_IRQ_PRIO_MASKING)
> : "=&r" (flags), "+r" (daif_bits)
> - : "r" (GIC_PRIO_IRQOFF)
> + : "r" ((unsigned long) GIC_PRIO_IRQOFF)
> : "memory");
>
> return flags;
> --
> 1.9.1
>
>
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