Re: [PATCH v10 12/25] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking

[Julien Thierry <julien.thierry@arm.com>]

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?

Thanks,

-- 
Julien Thierry


-->

From e839dec632bbf440efe8314751138ba46324078c Mon Sep 17 00:00:00 2001
From: Julien Thierry <julien.thierry@arm.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@gmail.com>
Signed-off-by: Julien Thierry <julien.thierry@arm.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