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Re: [PATCH] Fix unsafe function attributes for special functions (PR 71876)


On Wed, 20 Jul 2016, Bernd Edlinger wrote:

> On 07/20/16 12:46, Richard Biener wrote:
> > On Wed, 20 Jul 2016, Richard Biener wrote:
> >
> >> On Tue, 19 Jul 2016, Bernd Edlinger wrote:
> >>
> >>> Hi!
> >>>
> >>> As discussed at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71876,
> >>> we have a _very_ old hack in gcc, that recognizes certain functions by
> >>> name, and inserts in some cases unsafe attributes, that don't work for
> >>> a freestanding environment.
> >>>
> >>> It is unsafe to return ECF_MAY_BE_ALLOCA, ECF_LEAF and ECF_NORETURN
> >>> from special_function_p, just by the name of the function, especially
> >>> for less well known functions, like "getcontext" or "savectx", which
> >>> could easily used for something completely different.
> >>
> >> Returning ECF_MAY_BE_ALLOCA is safe.  Just wanted to mention this,
> >> regardless of the followups you already received.
> >
> > Oh, and maybe you can factor out the less controversical parts,
> > namely ignoring the __builtin_ prefix.  I don't think that
> > calling __builtin_setjmp in an environment where setjmp is not a
> > builtin should beave like setjmp (it will call a function named
> > '__builtin_setjmp').
> 
> 
> I wonder how I manage to dig out such contriversical things ;)
> 
> But you are right, that would at least be a start.
> 
> So this patch is what you requested:
> 
> Remove the handling of the __builtin_ prefix from special_function_p
> and add the returns_twice attribute to the __builtin_setjmp declaration
> instead.
> 
> Is it OK after boot-strap and regression-testing?

I think the __builtin_setjmp change is wrong - __builtin_setjmp is
_not_ 'setjmp' it is part of the GCC internal machinery (using setjmp
and longjmp in the end) for SJLJ exception handing.

Am I correct Eric?

Thanks,
Richard.

> 
> Thanks
> Bernd.
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)


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