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Date: Wed, 15 Jan 2020 14:50:47 +0100
From: Florian Weimer <fweimer@...hat.com>
To: Luís Marques <luismarques@...risc.org>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] Fix RISC-V a_cas inline asm operand sign extension
* Luís Marques:
> This patch adds an explicit cast to the int arguments passed to the inline asm
> used in the RISC-V's implementation of `a_cas`, to ensure that they are properly
> sign extended to 64 bits. They aren't automatically sign extended by Clang, and
> GCC technically also doesn't guarantee that they will be sign extended.
>
> ---
> arch/riscv64/atomic_arch.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv64/atomic_arch.h b/arch/riscv64/atomic_arch.h
> index 41ad4d04..0c382588 100644
> --- a/arch/riscv64/atomic_arch.h
> +++ b/arch/riscv64/atomic_arch.h
> @@ -15,7 +15,7 @@ static inline int a_cas(volatile int *p, int t, int s)
> " bnez %1, 1b\n"
> "1:"
> : "=&r"(old), "=&r"(tmp)
> - : "r"(p), "r"(t), "r"(s)
> + : "r"(p), "r"((long)t), "r"((long)s)
> : "memory");
> return old;
> }
Are casts in this place really casts, and not merely type assertions?
I think you have to use a temporarily variable or maybe a redundant +,
to change the syntax.
Thanks,
Florian
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