Messages in this thread | | | From | Nick Desaulniers <> | Date | Mon, 13 Sep 2021 13:50:17 -0700 | Subject | Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl() |
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On Mon, Sep 13, 2021 at 1:42 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Mon, Sep 13, 2021 at 1:16 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > > > Do we have access to _Generic in GCC 4.9? > > We've ended up using it unconditionally since last year, so yes.
Sorry, grepping would have taken < 1s. I'm very lazy. http://threevirtues.com/
> > In fact, the compiler version tests got removed when we raised the gcc > version requirement to 4.9 in commit 6ec4476ac825 ("Raise gcc version > requirement to 4.9"): > > "In particular, raising the minimum to 4.9 means that we can now just > assume _Generic() exists, which is likely the much better replacement > for a lot of very convoluted built-time magic with conditionals on > sizeof and/or __builtin_choose_expr() with same_type() etc" > > but we haven't used it much since. > > The "seqprop" code for picking the right lock for seqlock is perhaps > the main example, and staring at that code will make you go blind, so > look away.
Looking at my patch: https://lore.kernel.org/stable/20210913203201.1844253-1-ndesaulniers@google.com/ I don't think _Generic helps us in the case of dispatching based on the result of is_signed_type() (the operands could undergo type promotion, so we'd need lots of cases that are more concisely covered by is_signed_type()). It could replace the nested checks in div_64 with nested _Generics, I think. Not sure it's a huge win for readability. Maybe cut the number of expansions of the parameters in half though. Let me give it a try just to see what it looks like. -- Thanks, ~Nick Desaulniers
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