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SubjectRe: [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@southpole.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@southpole.se>
>> Signed-off-by: Stafford Horne <shorne@gmail.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;
>
>

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