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

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Message-ID: <alpine.LFD.2.20.1609192343330.2352@lianli.shorne-pla.net>
Date:   Mon, 19 Sep 2016 23:47:47 +0900 (JST)
From:   Stafford Horne <shorne@...il.com>
To:     Jonas Bonn <jonas@...thpole.se>
cc:     Stafford Horne <shorne@...il.com>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] Apply transparent_union attribute to union semun



On Mon, 19 Sep 2016, Jonas Bonn wrote:

> 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?

Hi Jonas,

This was also pointed out by the automated kbuild system and I replied on 
it. I am currently looking at a possible fix of adding an abi compat layer 
similar to what arm does with 'arch/arm/kernel/sys_oabi-compat.c'.

By toolchain being broken do you mean the openrisc abi spec is broken as 
well?  Last I checked gcc does compile as per the spec.  But it is not a 
very good spec.  There have been discussions to change this as well but no 
progress.

-Stafford

> 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;
>
>