Re: xmalloc calling undeclared xalloc_die function

[Bruno Haible <bruno@clisp.org>]

Florian Weimer wrote:
> lib/xmalloc.c contains this function definition, unconditionally:
> 
>   static void * _GL_ATTRIBUTE_PURE
>   nonnull (void *p)
>   {
>     if (!p)
>       xalloc_die ();
>     return p;
>   }
> 
> But the declaration of xalloc_die in lib/xalloc.h is conditional:
> 
>   #if GNULIB_XALLOC_DIE
>   
>   /* This function is always triggered when memory is exhausted.
>      It must be defined by the application, either explicitly
>      or by using gnulib's xalloc-die module.  This is the
>      function to call when one wants the program to die because of a
>      memory allocation failure.  */
>   /*extern*/ _Noreturn void xalloc_die (void);
>   
>   #endif /* GNULIB_XALLOC_DIE */

It's conditional on the C macro GNULIB_XALLOC_DIE, which is defined by
the module 'xalloc-die' (file modules/xalloc-die, line 15).

This conditional was added through
  <https://lists.gnu.org/archive/html/bug-gnulib/2020-10/msg00140.html>
1) to avoid link errors with a compiler that does not eliminate unused
   inline functions,
2) to trigger a compilation error instead of a link error or runtime error
   when a packages requerts 'xalloc-die' without 'xalloc' or vice versa
   but then actually uses both.

> I have a package (lbzip2 <https://github.com/kjn/lbzip2/>) which
> supplies its own definition of xalloc_die, and fails to build due to an
> undeclared function.

This package calls gnulib-tool like this:

  gnulib-tool --avoid=xalloc-die --add-import pthread utimens warnings \
      timespec-add timespec-sub dtotimespec stat-time lstat malloc-gnu \
      fprintf-posix inttypes xalloc largefile gitlog-to-changelog

This means, the module 'xalloc-die' is not included, thus xalloc.h does
not provide the declaration of xalloc_die().

There are at least three possible fixes:

  * Rather than '--avoid=xalloc-die', the package could override parts
    of the 'xalloc-die' module, as described in
    <https://www.gnu.org/software/gnulib/manual/html_node/Extending-Gnulib.html>.

  * The package could define the C macro GNULIB_XALLOC_DIE.

  * The package could declare xalloc_die().

I would probably pick the second one.

Bruno