Re: _NEWLIB_VERSION exposure through sys/cdefs.h

[Jonathan Roelofs <jonathan at codesourcery dot com>]

On 9/17/14 3:51 PM, Craig Howland wrote:
> 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:
> >
> > #ifdef _MACHINE__DEFAULT_TYPES_H
> >
> > 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)
>    ...
> #endif
> 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.)
Ah, good point. I do agree that __NEWLIB__ would be nice to have in either 
features.h or sys/cdefs.h though.


Thanks,

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

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