_NEWLIB_VERSION exposure through sys/cdefs.h

Craig Howland howland@LGSInnovations.com
Wed Sep 17 21:51:00 GMT 2014

On 09/17/2014 05:47 PM, Jeff Johnston wrote:
> ----- Original Message -----
>> From: "Jonathan Roelofs" <jonathan@codesourcery.com>
>> To: newlib@sourceware.org, "Corinna Vinschen" <vinschen@redhat.com>
>> Cc: "Dan Albert" <danalbert@google.com>, "JF Bastien" <jfb@chromium.org>
>> Sent: Wednesday, September 17, 2014 5:09:32 PM
>> Subject: _NEWLIB_VERSION exposure through sys/cdefs.h
>> Corinna,
>> In libc++, we'd like to be able to tell when the underlying libc is Newlib.
>> At
>> the moment, that requires us to do things like this:
>> #if defined(__has_include) && __has_include(<newlib.h>)
>> #include <newlib.h>
>> #endif
>> #if defined(_NEWLIB_VERSION)
>> ...
>> #endif
>> The problem with that strategy is that it does not work when using gcc, as it
>> doesn't have __has_include support yet.  It came up in discussion that
>> sys/cdefs.h might be the right place for that, as that's where glibc puts
>> __GLIBC__.
>> Would there be an objection to #include <newlib.h> from sys/cdefs.h?  Is
>> there a
>> better way to detect Newlib that I've overlooked?
> Hi Jonathan,
> Corinna is on vacation until Oct 8th.
> My version of glibc has __GLIBC__ defined in features.h which in glibc is
> included by sys/cdefs.h.
> I wouldn't have a problem with simply adding a __NEWLIB__ macro in newlib's
> features.h.  I also wouldn't have a real problem with including newlib.h from sys/cdefs.h
> though I notice one of the newlib.h macros is missing an underscore and needs to be fixed.
> A way of solving your problem now would be to look for:
> that is set by <machine/_default_types.h> which is a newlib-specific header
> that is included by sys/cdefs.h.  I don't see any platform overriding sys/cdefs.h
> except for x86-linux and it eventually includes <machine/_default_types.h> as
> well.
> Regards,
> -- Jeff J.
newlib.h gets included for almost every (and maybe even all) of the include 
files, as _ansi.h includes it.  So you should be able to include just about 
anything that you cared to and check for _NEWLIB_VERSION.  So, for example,
#include <stdio.h>
#if defined(_NEWLIB_VERSION)
works.  (This is more clear than _MACHINE_DEFAULT_TYPE_H and saves needing to 
add __NEWLIB__ as Jeff suggests.  Although the latter is not a bad idea.)

>> Cheers,
>> Jon
>> --
>> Jon Roelofs
>> jonathan@codesourcery.com
>> CodeSourcery / Mentor Embedded

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