Re: Divergence from BSD sources, e.g. __GNUC_PREREQ()

[Ralf Corsepius <ralf dot corsepius at rtems dot org>]

On 04/04/2013 09:59 AM, Sebastian Huber wrote:
> Hello,
>
> I have some questions about the divergence from BSD sources.  The
> background is that <sys/queue.h> is broken in Newlib since __offsetof()
> is undefined.  I wanted to update the file in Newlib with the latest
> version from FreeBSD, but now some problems arise.
>
> What is the purpose of <sys/cdefs.h> in Newlib?

Like the bsd version, it's an internal libc header, whose only purpose 
is to provide some internal defines and not meant to be used in 
applications.

>  This file seems to be
> derived from BSD sources, but current BSD versions look quite
> different.

Correct, they were forked long time ago and now have diverged. That 
said, though they have common origins, BSD actually isn't of actual 
interest here and even less so FreeBSD-compatibility, IMO.

>  For example last year the new macro __GNUC_PREREQ() was
> introduced in "libc/include/sys/features.h":
>
> /* Macro to test version of GCC.  Returns 0 for non-GCC or too old GCC. */
> #ifndef __GNUC_PREREQ
> # if defined __GNUC__ && defined __GNUC_MINOR__
> #  define __GNUC_PREREQ(maj, min) \
>      ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
> # else
> #  define __GNUC_PREREQ(maj, min) 0
> # endif
> #endif /* __GNUC_PREREQ */
>
> In FreeBSD we have a similar macro in <sys/cdefs.h>:
>
> http://svnweb.freebsd.org/base/head/sys/sys/cdefs.h?revision=241374
>
> /*
>   * Macro to test if we're using a specific version of gcc or later.
>   */
> #if defined(__GNUC__) && !defined(__INTEL_COMPILER)
> #define    __GNUC_PREREQ__(ma, mi)    \
>      (__GNUC__ > (ma) || __GNUC__ == (ma) && __GNUC_MINOR__ >= (mi))
> #else
> #define    __GNUC_PREREQ__(ma, mi)    0
> #endif
>
> Why don't we follow the BSD development more to simplify code re-use?

Please elaborate the bug in newlib this would fix. icc has never been of 
interest to newlib, while __GNUC_PREREQ can't be removed without 
introducing incompatibilities in newlib.

Also note that newlib's __GNUC_PREREQ and FreeBSD's __GNUC_PREREQ__ are 
not interchangable (__GNUC_PREREQ can be used for version comparison, 
__GNUC_PREREQ__ is binary).

> The latest version of FreeBSD <sys/queue.h> uses __containerof():

IMO, this is a FreeBSD implementation detail, newlib may or may not 
adopt for BSD compatibility.

That said, I am against adopting it, because "FreeBSD sys/queue.h" has a 
history FreeBSD changing it ad-lib, which means any attempt to provide 
FreeBSD compatibility will fail in longer terms.

Ralf