Re: [PATCH v5] libio: Add nonnull attribute for most FILE * arguments in stdio.h

[Xi Ruoyao <xry111@xry111.site>]

On Mon, 2023-07-10 at 15:31 -0400, Siddhesh Poyarekar wrote:
> On 2023-07-10 14:56, Zack Weinberg wrote:
> > > Would it be more acceptable to you if this gets wrapped into fortify,
> > > i.e. it gets enabled if _FORTIFY_SOURCE is defined?
> > 
> > I tend to agree with Xi that having the presence of __nonnull depend on
> > _FORTIFY_SOURCE would cause more problems than it solves.  Also, since
> > several Linux distributions enable _FORTIFY_SOURCE by default, we'd
> > still be risking significant breakage if we shipped that in 2.38.
> 
> I'm less concerned about the distribution breakage because they'll more 
> likely than not get fixed; in fact my suggestion to put it behind the 
> _FORTIFY_SOURCE wall was precisely for that reason.  I'd like us to weed 
> out such cases in the distribution and get them fixed rather than 
> maintaining status quo.  I'm relatively more concerned about 
> non-distribution applications that tend to, e.g. disable security 
> features because they see them as either performance hindrances or want 
> some legacy broken code to just work.
> 
> Of course, I'm not concerned enough about these applications (sorry) to 
> insist that it be put behind _FORTIFY_SOURCE, but I think it's a 
> reasonable compromise.  That doesn't directly solve the analyzer problem 
> though.  Maybe if it's OK to have the analyzer affect codegen, we could 
> have the analyzer define _FORTIFY_SOURCE=3 and thus enable additional 
> diagnostics too, like the __wur that also gets enabled only on 
> fortification.  Is that something worth considering?

Or can we just guard the __nonnull usage against __GNUC_PREREQ (x, 0)
where x is 12 or 13?  In the recent GCC releases the optimizer won't
kill a side effect before an UB so it should be much safer (see my reply
to Zack), and it's unlikely they'll use the latest GCC for some legacy
broken code.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University