Re: Autoconf stanza to test for Newlib?

[Jeffrey Walton <noloader at gmail dot com>]

On Wed, Nov 8, 2017 at 4:23 PM, Hans-Bernhard Bröker
<HBBroeker@t-online.de> wrote:
> Am 08.11.2017 um 01:13 schrieb Jeffrey Walton:
>> ...
>> We are trying to add Autoool support to an existing library. We don't
>> do much of anything special if Newlib is the runtime library. We just
>> need to add an _XOPEN_SOURCE=600.
>
> It doesn't make terribly much sense to have to define such a macro only for
> Newlib.  If your code needs that macro for Newlib, it'll need it for all
> libc implementations, or at least all that do know about it.
>
> Given that, I believe you should be looking for
>
>         AC_USE_SYSTEM_EXTENSIONS

Thanks Hans.

I wanted to give this some more thought before replying, so sorry
about the late reply. I know the issue you are referring to -
libstdc++ running fast and loose, and making too many symbols
available in C++ by default.

At this point I think I would like to solve the concrete problem that
exists rather than problems that don't exist. (with the understanding
I may have to do it in the future).

I'm currently using:

  AC_MSG_CHECKING([if runtime library is Newlib])
  AC_PREPROC_IFELSE([AC_LANG_PROGRAM([#include <_newlib_version.h>])],
    [AC_MSG_RESULT([yes]); AC_SUBST([tr_RESULT], [1])],
    [AC_MSG_RESULT([no]); AC_SUBST([tr_RESULT], [0])]
  )

because the head notes in <_newlib_version.h> state its OK for
downstream to use. But I am not sure this is the best test to use
since its mostly static and does not take compiler defaults and
CXXFLAGS into account.

I guess my next question is, should we be checking the preprocessor
for a symbol like __NEWLIB__?

Jeff