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

On 04/04/2013 09:59 AM, Sebastian Huber wrote:

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

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>:

  * 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))
#define    __GNUC_PREREQ__(ma, mi)    0

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.


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