On Wed, 8 Jan 2025 at 11:42, Frank Mehnert <[email protected]> wrote: > > Hi Kjetil, > > On Dienstag, 7. Januar 2025 18:18:14 MEZ Kjetil Oftedal wrote: > > On Tue, 7 Jan 2025 at 18:07, Frank Mehnert > > <[email protected]> wrote: > > > > > > On Dienstag, 7. Januar 2025 17:38:52 MEZ Kjetil Oftedal wrote: > > > > On Tue, 7 Jan 2025 at 17:09, Frank Mehnert > > > > <[email protected]> wrote: > > > > > > > > [...] > > > > > > > > Is this true for all cases for strings? > > > > > > > > > In the original case (end_ptr < str), the compiler knows for sure that > > > > > both pointers belong to different objects! > > > > > > > > --- > > > > const char* str = "Hello World!" > > > > const char* sub_str = strstr(str, "Wor"); > > > > > > > > strnlen(sub_str, X); > > > > --- > > > > > > > > For some values of X end_ptr is still pointing to a valid array entry > > > > for the original "Hello World" string, > > > > even if it is not within the "World!" substring. Is it then not > > > > pointing to a valid array of objects? > > > > (E.g if X is the unsigned representation of -1,-2,...-6) > > > > > > OK, I think you have a point. > > > > > > Basically this derives into the question if adding a huge offset to a > > > pointer > > > is the same as subtracting a small offset from a pointer. So far I > > > couldn't > > > find any C++ rule related to this problem. > > > > Hi, > > > > I think it is purely academic as this point though :) > > > > The change is probably fine. Just a bit annoyed that clang forces > > changes to the code > > in a lot of projects, instead of clang accepting defacto standard patterns. > > The LLVM ticket [1] was updated and Andrew Pinski noted that the the Linux > kernel, -fwrapv-pointer was added to keep the "defacto standard patterns". > So compiling with -fno-strict-overflow (which included -fwrapv-pointer) would > most likely make my fix superfluous. > > So it's basically about pointer arithmetics warp around. > > But I hope there is agreement now that my change makes the code "more > correct". > > Kind regards > > Frank > > [1] https://github.com/llvm/llvm-project/issues/121909 > -- > Dr.-Ing. Frank Mehnert, [email protected], +49-351-41 883 224 > > Kernkonzept GmbH. Sitz: Dresden. Amtsgericht Dresden, HRB 31129. > Geschäftsführer: Dr.-Ing. Michael Hohmuth >
Sure. I enjoyed the discussion. There is no objection from me on the change. Best regards, Kjetil Oftedal _______________________________________________ devel mailing list -- [email protected] To unsubscribe send an email to [email protected]
