linux-kernel - Re: [PATCH] prctl: implement PR_GET

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Message-Id: <20170131162624.5a85ec47c6ee22e5cc03c4eb@linux-foundation.org>
Date:   Tue, 31 Jan 2017 16:26:24 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Helge Deller <deller@....de>
Cc:     linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        Michael Kerrisk <mtk.manpages@...glemail.com>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] prctl: implement PR_GET_ENDIAN for all architectures

On Sat, 28 Jan 2017 12:13:10 +0100 Helge Deller <deller@....de> wrote:

> The prctl(PR_GET_ENDIAN) syscall was added to Kernel 2.6.18, but
> implemented for PowerPC only.
> This trivial patch adds support for this syscall for all other architectures.

Seems reasonable.  I guess.  Why is this needed?

The man page will need updating.  It says "PowerPC only".

> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 842914e..5818e5e 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -79,9 +79,6 @@
>  #ifndef GET_FPEXC_CTL
>  # define GET_FPEXC_CTL(a, b)	(-EINVAL)
>  #endif
> -#ifndef GET_ENDIAN
> -# define GET_ENDIAN(a, b)	(-EINVAL)
> -#endif
>  #ifndef SET_ENDIAN
>  # define SET_ENDIAN(a, b)	(-EINVAL)
>  #endif
> @@ -2136,7 +2133,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			return -EFAULT;
>  		break;
>  	case PR_GET_ENDIAN:
> +#ifdef GET_ENDIAN
>  		error = GET_ENDIAN(me, arg2);
> +#elif defined(__BIG_ENDIAN)
> +		error = put_user(PR_ENDIAN_BIG, (unsigned int __user *)arg2);
> +#else
> +		error = put_user(PR_ENDIAN_LITTLE, (unsigned int __user *)arg2);
> +#endif
>  		break;
>  	case PR_SET_ENDIAN:
>  		error = SET_ENDIAN(me, arg2);