Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))

[Luc Van Oostenryck]

On Thu, Dec 12, 2019 at 09:53:38PM +0100, Peter Zijlstra wrote:
> Now, looking at the current GCC source:
> 
>   https://github.com/gcc-mirror/gcc/blob/97d7270f894395e513667a031a0c309d1819d05e/gcc/c/c-parser.c#L3707
> 
> it seems that __typeof__() is supposed to strip all qualifiers from
> _Atomic types. That lead me to try:
> 
> 	typeof(_Atomic typeof(p)) __p = (p);
> 
> But alas, I still get the same junk you got for ool_store_release() :/

I was checking this to see if Sparse was ready to support this.
I was a bit surprised because at first sigth GCC was doing as
it claims (typeof striping const & volatile on _Atomic types)
but your exampe wasn't working. But it's working if an
intermediate var is used:
	_Atomic typeof(p) tmp;
	typeof(tmp) __p = (p);
or, uglier but probably more practical:
	typeof(({_Atomic typeof(p) tmp; })) __p = (p);

Go figure!

OTOH, at least on GCC 8.3, it seems to always do the same with
volatiles than it does with consts.

-- Luc Van Oostenryck