Re: {put,get}_user() side effects

[Andreas Schwab <schwab@suse.de>]

Horst von Brand <vonbrand@inf.utfsm.cl> writes:

> Geert Uytterhoeven <geert@linux-m68k.org> said:
>> On Tue, 6 Apr 2004, Andi Kleen wrote:
>> > Geert Uytterhoeven <geert@linux-m68k.org> writes:
>> > > On most (all?) architectures {get,put}_user() has side effects:
>> > >
>> > > #define put_user(x,ptr)                                                 \
>> > >   __put_user_check((__typeof__(*(ptr)))(x),(ptr),sizeof(*(ptr)))
>> >
>> > Neither typeof not sizeof are supposed to have side effects. If your
>> > compiler generates them that's a compiler bug.
>
>> From a simple compile test, you seem to be right... Weird, since it does
>> expand to 3 times 'pIndex++', but pIndex is incremented only once.
>
> Better check with a C language lawyer. Maybe gcc gets it wrong, or it is
> undefined

It's not undefined, the standard explicitly says that the argument of
sizeof is not evaluated (unless its type is a VLA).  I can't remember gcc
ever getting that wrong.

Andreas.

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Andreas Schwab, SuSE Labs, schwab@suse.de
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