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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc: Make set_endian() return EINVAL when not supporting little endian
Date: Thu, 26 Aug 2021 13:41:39 +1000	[thread overview]
Message-ID: <87bl5kc1os.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <b29c29d205737a833262df38e01c07139f1c3dec.1629899011.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> There is no point in modifying MSR_LE bit on CPUs not supporting
> little endian.

Isn't that an ABI break?

set_endian(PR_ENDIAN_BIG) should work on a big endian CPU, even if it
does nothing useful.

cheers

> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 185beb290580..b2b9919795a2 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1995,6 +1995,10 @@ int set_endian(struct task_struct *tsk, unsigned int val)
>  {
>  	struct pt_regs *regs = tsk->thread.regs;
>  
> +	if (!cpu_has_feature(CPU_FTR_PPC_LE) &&
> +	    !cpu_has_feature(CPU_FTR_REAL_LE))
> +		return -EINVAL;
> +
>  	if ((val == PR_ENDIAN_LITTLE && !cpu_has_feature(CPU_FTR_REAL_LE)) ||
>  	    (val == PR_ENDIAN_PPC_LITTLE && !cpu_has_feature(CPU_FTR_PPC_LE)))
>  		return -EINVAL;
> -- 
> 2.25.0

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc: Make set_endian() return EINVAL when not supporting little endian
Date: Thu, 26 Aug 2021 13:41:39 +1000	[thread overview]
Message-ID: <87bl5kc1os.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <b29c29d205737a833262df38e01c07139f1c3dec.1629899011.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> There is no point in modifying MSR_LE bit on CPUs not supporting
> little endian.

Isn't that an ABI break?

set_endian(PR_ENDIAN_BIG) should work on a big endian CPU, even if it
does nothing useful.

cheers

> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 185beb290580..b2b9919795a2 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1995,6 +1995,10 @@ int set_endian(struct task_struct *tsk, unsigned int val)
>  {
>  	struct pt_regs *regs = tsk->thread.regs;
>  
> +	if (!cpu_has_feature(CPU_FTR_PPC_LE) &&
> +	    !cpu_has_feature(CPU_FTR_REAL_LE))
> +		return -EINVAL;
> +
>  	if ((val == PR_ENDIAN_LITTLE && !cpu_has_feature(CPU_FTR_REAL_LE)) ||
>  	    (val == PR_ENDIAN_PPC_LITTLE && !cpu_has_feature(CPU_FTR_PPC_LE)))
>  		return -EINVAL;
> -- 
> 2.25.0

  reply	other threads:[~2021-08-26  3:42 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25 13:43 [PATCH] powerpc: Make set_endian() return EINVAL when not supporting little endian Christophe Leroy
2021-08-25 13:43 ` Christophe Leroy
2021-08-26  3:41 ` Michael Ellerman [this message]
2021-08-26  3:41   ` Michael Ellerman
2021-08-26  4:55   ` Christophe Leroy
2021-08-26  4:55     ` Christophe Leroy
2021-08-26 14:23     ` Michael Ellerman
2021-08-26 14:23       ` Michael Ellerman

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