Re: [[GCC13][Patch][V3] 1/2] Add a new option -fstrict-flex-array[=n] and new attribute strict_flex_array

[Kees Cook <keescook@chromium.org>]

On Wed, Aug 31, 2022 at 08:16:49PM +0000, Qing Zhao wrote:
> 
> > On Aug 31, 2022, at 4:09 PM, Joseph Myers <joseph@codesourcery.com> wrote:
> > 
> > On Wed, 31 Aug 2022, Qing Zhao wrote:
> > 
> >>>> When -std=gnu89 + -fstrict-flex-array=3 (ONLY C99 flexible array member 
> >>>> [] is treated as a valid flexible array) present together,
> >>> 
> >>> That seems reasonable enough without a warning.  If people want a warning 
> >>> for flexible array members in older language modes, they can use 
> >>> -pedantic; I don't think we need to warn for any particular 
> >>> -fstrict-flex-array modes there.
> >> 
> >> So, you mean,
> >> 
> >> 1. GCC with -std=gnu89 support all [0], [1], and [] as Flexible array member;
> >> 2. Therefore. -std=gnu89 + -fstrict-flex-array=3 does not need a warning;
> >> 
> >> ?
> > 
> > Yes.
> > 
> >> Then, how about:
> >> 
> >> -std=c89:
> >> 
> >> 1. GCC with -std=c89 also support all [0], [1], and [] as Flexible array member;
> >> 2, therefore, -std=c89 + -fstrict-flex-array does not need a warning too.
> >> 
> >> ?
> > 
> > Yes.
> > 
> 
> Okay, I am fine with this.
> 
> Richard and Kees,  what’s your opinion on this?

Agreed: I think it's fine not to warn about these "conflicting" flags in
those cases. It looks like the C standard warnings about flexible arrays
are already hidden behind -Wpedantic, so nothing else is needed, IMO.
Using -fstrict-flex-arrays just enforces that warning. ;)

-- 
Kees Cook