R devel - Oct 2013 - Compiler warning: function returns address of local variable

I am a Gentoo user. I have just upgraded my Gentoo system,
as I usually do every Saturday. During this process, my previous
dev-lang/R-2.10.1 ebuild package has been upgraded to R-3.0.1.
While compiling it, I have got the following compiler warning:

 * QA Notice: Package triggers severe warnings which indicate that it
 *            may exhibit random runtime failures.
 * main.c:1548:5: warning: function returns address of local variable
[enabled by default]

 * Please do not file a Gentoo bug and instead report the above QA
 * issues directly to the upstream developers of this software.
 * Homepage: http://www.r-project.org/

The Bug Tracking page of www.r-project.org simply do not open.
So, I've just subscribed to this mailing list to post this compiler
warning here.

	[[alternative HTML version deleted]]

On 05/10/2013 20:48, Gevis Inko wrote:
> I am a Gentoo user. I have just upgraded my Gentoo system,
> as I usually do every Saturday. During this process, my previous
> dev-lang/R-2.10.1 ebuild package has been upgraded to R-3.0.1.
> While compiling it, I have got the following compiler warning:
>
>   * QA Notice: Package triggers severe warnings which indicate that it
>   *            may exhibit random runtime failures.
>   * main.c:1548:5: warning: function returns address of local variable
> [enabled by default]
>
>   * Please do not file a Gentoo bug and instead report the above QA
>   * issues directly to the upstream developers of this software.
>   * Homepage: http://www.r-project.org/
>
> The Bug Tracking page of www.r-project.org simply do not open.
It was down for a few days whilst the hardware was moved to another 
site.  It is up now at https://rbugs.urbanek.info/bugzilla3/, and 
hopefully will be available again as bugs.r-project.org today.
> So, I've just subscribed to this mailing list to post this compiler
> warning here.
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
That is the whole point of that piece of C code, so please do report the 
Gentoo bug (their message is simply bogus) to them.

And also read posting guide before posting: HTML mail is not allowed here.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

> > ..., my previous
> > dev-lang/R-2.10.1 ebuild package has been upgraded to R-3.0.1.
> > While compiling it, I have got the following compiler warning:
> >
> >   * QA Notice: Package triggers severe warnings which indicate that it
> >   *            may exhibit random runtime failures.
> >   * main.c:1548:5: warning: function returns address of local variable
> > [enabled by default]
> >
> >   * Please do not file a Gentoo bug and instead report the above QA
> >   * issues directly to the upstream developers of this software.
> >   * Homepage: http://www.r-project.org/
> That is the whole point of that piece of C code, so please do report the 
> Gentoo bug (their message is simply bogus) to them.
> 
> And also read posting guide before posting: HTML mail is not allowed here.
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk

The message is certainly not "simply bogus".  Returning the address of
a local variable is almost always a bug.

In this case, there is no real bug in R-3.0.1, since the result is
used for the low-level, system-dependent operation of determining the
direction of stack growth, but this is a very rare use.  For the
compiler to issue such a warning is fully justified.

The warning could be avoided by using the approach taken in pqR, which
has the following routine in main.c:

  /* Detemine whether the stack grows down (+1) or up (-1).  Passed the
     address of a local variable in the caller's stack frame.
  
     This is put here, though called only from system.c, so that the compiler
     will not be able to inline it. */
  
  int R_stack_growth_direction (uintptr_t cvaraddr)
  {
      int dummy;
      return (uintptr_t) &dummy < cvaraddr ? 1 : -1;
  }