Messages in this thread |  | | Subject | Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) | From | Christian Borntraeger <> | Date | Wed, 18 Dec 2019 11:22:05 +0100 |
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On 12.12.19 21:49, Linus Torvalds wrote: > On Thu, Dec 12, 2019 at 11:34 AM Will Deacon <will@kernel.org> wrote: >> >> The root of my concern in all of this, and what started me looking at it in >> the first place, is the interaction with 'typeof()'. Inheriting 'volatile' >> for a pointer means that local variables in macros declared using typeof() >> suddenly start generating *hideous* code, particularly when pointless stack >> spills get stackprotector all excited. > > Yeah, removing volatile can be a bit annoying. > > For the particular case of the bitops, though, it's not an issue. > Since you know the type there, you can just cast it. > > And if we had the rule that READ_ONCE() was an arithmetic type, you could do > > typeof(0+(*p)) __var; > > since you might as well get the integer promotion anyway (on the > non-volatile result). > > But that doesn't work with structures or unions, of course.
We do have a READ_ONCE on the following union in s390 code.
union ipte_control { unsigned long val; struct { unsigned long k : 1; unsigned long kh : 31; unsigned long kg : 32; }; };
In fact this one was the original failure case why we change ACCESS_ONCE.
see arch/s390/kvm/gaccess.c
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