linux-kernel - Re: [PATCH 1/7] Apply transparent

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Message-ID: <57DFF593.9030200@southpole.se>
Date:   Mon, 19 Sep 2016 16:26:27 +0200
From:   Jonas Bonn <jonas@...thpole.se>
To:     Stafford Horne <shorne@...il.com>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] Apply transparent_union attribute to union semun

NAK... this breaks other architectures.

The OpenRISC toolchain is broken with regard to this issue.  Five years 
ago (last I looked) nobody seemed interesting in fixing it. Has anything 
changed here?

/Jonas

On 09/16/2016 04:42 PM, Stafford Horne wrote:
> ..From: Jonas Bonn <jonas@...thpole.se>
>
> The syscall handler for semctl is written under the assumption that the
> toolchain will pass "small" unions as function parameters directly instead
> of by reference.  The union semun is "small" and thus fits this description.
>
> Since it is assumed that the union will be passed directly and not by
> reference, it is safe to access the union members without going via
> get_user.
>
> The OpenRISC architecture, however, passes all unions by reference, thus
> breaking the above assumption.
>
> The technically correct fix here is to mark the union as being transparent
> so that the ABI of the union's first element determines the parameter
> passing method and thus make explicit what's already implied in the function
> definition.
>
> Signed-off-by: Jonas Bonn <jonas@...thpole.se>
> Signed-off-by: Stafford Horne <shorne@...il.com>
> ---
>   include/uapi/linux/sem.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/sem.h b/include/uapi/linux/sem.h
> index dd73b90..aabe50f 100644
> --- a/include/uapi/linux/sem.h
> +++ b/include/uapi/linux/sem.h
> @@ -48,7 +48,7 @@ union semun {
>   	unsigned short __user *array;	/* array for GETALL & SETALL */
>   	struct seminfo __user *__buf;	/* buffer for IPC_INFO */
>   	void __user *__pad;
> -};
> +} __attribute__ ((transparent_union));
>   
>   struct  seminfo {
>   	int semmap;