On Tue, Nov 22, 2022 at 03:02:04PM +0000, Qing Zhao wrote: > > > > On Nov 22, 2022, at 9:10 AM, Qing Zhao via Gcc-patches > > <gcc-patches@gcc.gnu.org> wrote: > > > > > > > >> On Nov 22, 2022, at 3:16 AM, Richard Biener <rguent...@suse.de> wrote: > >> > >> On Mon, 21 Nov 2022, Qing Zhao wrote: > >> > >>> > >>> > >>>> On Nov 18, 2022, at 11:31 AM, Kees Cook <keesc...@chromium.org> wrote: > >>>> > >>>> On Fri, Nov 18, 2022 at 03:19:07PM +0000, Qing Zhao wrote: > >>>>> Hi, Richard, > >>>>> > >>>>> Honestly, it?s very hard for me to decide what?s the best way to handle > >>>>> the interaction > >>>>> between -fstrict-flex-array=M and -Warray-bounds=N. > >>>>> > >>>>> Ideally, -fstrict-flex-array=M should completely control the behavior > >>>>> of -Warray-bounds. > >>>>> If possible, I prefer this solution. > >>>>> > >>>>> However, -Warray-bounds is included in -Wall, and has been used > >>>>> extensively for a long time. > >>>>> It?s not safe to change its default behavior. > >>>> > >>>> I prefer that -fstrict-flex-arrays controls -Warray-bounds. That > >>>> it is in -Wall is _good_ for this reason. :) No one is going to add > >>>> -fstrict-flex-arrays (at any level) without understanding what it does > >>>> and wanting those effects on -Warray-bounds. > >>> > >>> > >>> The major difficulties to let -fstrict-flex-arrays controlling > >>> -Warray-bounds was discussed in the following threads: > >>> > >>> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604133.html > >>> > >>> Please take a look at the discussion and let me know your opinion. > >> > >> My opinion is now, after re-considering and with seeing your new > >> patch, that -Warray-bounds=2 should be changed to only add > >> "the intermediate results of pointer arithmetic that may yield out of > >> bounds values" and that what it considers a flex array should now > >> be controlled by -fstrict-flex-arrays only. > >> > >> That is, I think, the only thing that's not confusing to users even > >> if that implies a change from previous behavior that we should > >> document by clarifying the -Warray-bounds documentation as well as > >> by adding an entry to the Caveats section of gcc-13/changes.html > >> > >> That also means that =2 will get _less_ warnings with GCC 13 when > >> the user doesn't use -fstrict-flex-arrays as well. > > > > Okay. So, this is for -Warray-bounds=2. > > > > For -Warray-bounds=1 -fstrict-flex-array=N, if N > 1, should > > -fstrict-flex-array=N control -Warray-bounds=1? > > More thinking on this. (I might misunderstand a little bit in the previous > email) > > If I understand correctly now, what you proposed was: > > 1. The level of -Warray-bounds will NOT control how a trailing array is > considered as a flex array member anymore. > 2. Only the level of -fstrict-flex-arrays will control this; > 3. Keep the current default behavior of -Warray-bounds on treating trailing > arrays as flex array member (treating all [0],[1], and [] as flexible array > members). > 4. Updating the documentation for -Warray-bounds by clarifying this change, > and also as an entry to the Caveats section on such change on -Warray-bounds. > > If the above is correct, Yes, I like this change. Both the user interface and > the internal implementation will be simplified and cleaner. > > Let me know if you see any issue with my above understanding. > > Thanks a lot.
FWIW, this matches what I think makes the most sense too. -- Kees Cook
