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Re: _NEWLIB_VERSION exposure through sys/cdefs.h

On 09/17/2014 05:47 PM, Jeff Johnston wrote:
----- Original Message -----
From: "Jonathan Roelofs" <>
To:, "Corinna Vinschen" <>
Cc: "Dan Albert" <>, "JF Bastien" <>
Sent: Wednesday, September 17, 2014 5:09:32 PM
Subject: _NEWLIB_VERSION exposure through sys/cdefs.h


In libc++, we'd like to be able to tell when the underlying libc is Newlib.
the moment, that requires us to do things like this:

#if defined(__has_include) && __has_include(<newlib.h>)
#include <newlib.h>
#if defined(_NEWLIB_VERSION)

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

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


-- 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.)




Jon Roelofs
CodeSourcery / Mentor Embedded

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