Re: [V2][PATCH 1/1] Add a new warning option -Wstrict-flex-arrays.

[Richard Biener <rguenther@suse.de>]

On Fri, 2 Dec 2022, Qing Zhao wrote:

> 
> 
> > On Dec 2, 2022, at 2:20 AM, Richard Biener <rguenther@suse.de> wrote:
> > 
> > On Fri, 2 Dec 2022, Richard Biener wrote:
> > 
> >> On Thu, 1 Dec 2022, Siddhesh Poyarekar wrote:
> >> 
> >>> On 2022-12-01 11:42, Kees Cook wrote:
> >>>> On Wed, Nov 30, 2022 at 02:25:56PM +0000, Qing Zhao wrote:
> >>>>> '-Wstrict-flex-arrays'
> >>>>>      Warn about inproper usages of flexible array members according to
> >>>>>      the LEVEL of the 'strict_flex_array (LEVEL)' attribute attached to
> >>>>>      the trailing array field of a structure if it's available,
> >>>>>      otherwise according to the LEVEL of the option
> >>>>>      '-fstrict-flex-arrays=LEVEL'.
> >>>>> 
> >>>>>      This option is effective only when LEVEL is bigger than 0.
> >>>>>      Otherwise, it will be ignored with a warning.
> >>>>> 
> >>>>>      when LEVEL=1, warnings will be issued for a trailing array
> >>>>>      reference of a structure that have 2 or more elements if the
> >>>>>      trailing array is referenced as a flexible array member.
> >>>>> 
> >>>>>      when LEVEL=2, in addition to LEVEL=1, additional warnings will be
> >>>>>      issued for a trailing one-element array reference of a structure if
> >>>>>      the array is referenced as a flexible array member.
> >>>>> 
> >>>>>      when LEVEL=3, in addition to LEVEL=2, additional warnings will be
> >>>>>      issued for a trailing zero-length array reference of a structure if
> >>>>>      the array is referenced as a flexible array member.
> >>>>> 
> >>>>> At the same time, -Warray-bounds is updated:
> >>>> 
> >>>> Why is there both -Wstrict-flex-arrays and -Warray-bounds? I thought
> >>>> only the latter was going to exist?
> >> 
> >> Sorry for appearantly not being clear - I was requesting 
> >> -Wstrict-flex-arrays to be dropped and instead adjusting -Warray-bounds
> >> to adhere to -fstrict-flex-arrays in both =1 and =2 where then =2
> >> would only add the intermediate pointer results verification.
> >> 
> >> I think that's reasonable if documented since the default behavior
> >> with -Wall will not change then unless the -fstrict-flex-arrays
> >> default is altered.
> > 
> > Btw, your patch seems to implement the above plus adds 
> > -Wstrict-flex-arrays.  It seems it could be split into two, doing
> > the -Warray-bounds adjustment as first and the -Wstrict-flex-arrays 
> > addition as second.
> 
> Yes, implementation should be very easy to be adjusted to drop the new -Wstrict-flex-arrays option.
> But I still feel the new -Wstrict-flex-arrays option is good to add.

Can you split the patch and re-post?  I'll quickly approve the first
part and will think harder on the second.

Thanks,
Richard.

> Qing
> >  We do all seem to agree on the first so it's easy
> > to go forward with that?
> > 
> > Thanks,
> > Richard.
> 
> 

-- 
Richard Biener <rguenther@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)