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. Richard. -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)
