Re: [gpsd-dev] patches from pkgsrc: SConstruct

[Greg Troxel]

> For example: _BSD_SOURCE is certainly not Linux only.  It is glibx.

Good catch, thanks.

> Please use TODO instead of \todo.  That is a keyword that triggers
> some tools we use.

OK - I'll try to remember that.  I didn't realize the local convention.

> I just re-verified.  This is not true:
>
> +        # required because _XOPEN_SOURCE above restricts visibility of
> +        # all things not defined by XOPEN
>
> Easy to confirm on netbad:
>
>     fgrep XOPEN_SOURCE /usr/include -r

I've attached sys/featuretest.h.  The issue of these visibility
definitions removing things that are beyond the standard has come up in
other places.  You can see that defining _XOPEN_SOURCE removes the
implied definition of _NETBSD_SOURCE.  This matches my understanding of
how this entire visibility scheme is supposed to work.

I wrote a test program (below) that trivially uses strlcpy.  This
function exists in NetBSD, but it's only available if _NETBSD_SOURCE is
defined (explicitly or implicitly) because it is not specified by POSIX.

The test program as appended fails to build (with -Werror, because of
not seeing a strlcpy prototype).  Without _XOPEN_SOURCE, or with
_NETBSD_SOURCE also, it builds without warnings.

This is what I was trying to say: by defining _XOPEN_SOURCE, one is not
only requesting that all functions defined by that XOPEN version be
visible, but also requesting that functions not defined by that version
be hidden.

Overall, I suspect that gpsd would be better off not defining *any*
visibility functions unless shown to be necessary, and then on those
platforms figuring out how to ask for all definitions.

----------------------------------------
#define _XOPEN_SOURCE 700

#include <stdio.h>
#include <string.h>

int main(int arg, char **argv)
{
    char dst[10], *src;
    size_t r;

    src = "A wicked long string more than 10 bytes.";

    r = strlcpy(dst, src, sizeof(dst));

    printf("retval %d string <%s>\n", r, dst);

    return 0;
}
---------------------------------------
/*      $NetBSD: featuretest.h,v 1.10 2013/04/26 18:29:06 christos Exp $        
*/

/*
 * Written by Klaus Klein <address@hidden>, February 2, 1998.
 * Public domain.
 *
 * NOTE: Do not protect this header against multiple inclusion.  Doing
 * so can have subtle side-effects due to header file inclusion order
 * and testing of e.g. _POSIX_SOURCE vs. _POSIX_C_SOURCE.  Instead,
 * protect each CPP macro that we want to supply.
 */

/*
 * Feature-test macros are defined by several standards, and allow an
 * application to specify what symbols they want the system headers to
 * expose, and hence what standard they want them to conform to.
 * There are two classes of feature-test macros.  The first class
 * specify complete standards, and if one of these is defined, header
 * files will try to conform to the relevant standard.  They are:
 *
 * ANSI macros:
 * _ANSI_SOURCE                 ANSI C89
 *
 * POSIX macros:
 * _POSIX_SOURCE == 1           IEEE Std 1003.1 (version?)
 * _POSIX_C_SOURCE == 1         IEEE Std 1003.1-1990
 * _POSIX_C_SOURCE == 2         IEEE Std 1003.2-1992
 * _POSIX_C_SOURCE == 199309L   IEEE Std 1003.1b-1993
 * _POSIX_C_SOURCE == 199506L   ISO/IEC 9945-1:1996
 * _POSIX_C_SOURCE == 200112L   IEEE Std 1003.1-2001
 * _POSIX_C_SOURCE == 200809L   IEEE Std 1003.1-2008
 *
 * X/Open macros:
 * _XOPEN_SOURCE                System Interfaces and Headers, Issue 4, Ver 2
 * _XOPEN_SOURCE_EXTENDED == 1  XSH4.2 UNIX extensions
 * _XOPEN_SOURCE == 500         System Interfaces and Headers, Issue 5
 * _XOPEN_SOURCE == 520         Networking Services (XNS), Issue 5.2
 * _XOPEN_SOURCE == 600         IEEE Std 1003.1-2001, XSI option
 * _XOPEN_SOURCE == 700         IEEE Std 1003.1-2008, XSI option
 *
 * NetBSD macros:
 * _NETBSD_SOURCE == 1          Make all NetBSD features available.
 *
 * If more than one of these "major" feature-test macros is defined,
 * then the set of facilities provided (and namespace used) is the
 * union of that specified by the relevant standards, and in case of
 * conflict, the earlier standard in the above list has precedence (so
 * if both _POSIX_C_SOURCE and _NETBSD_SOURCE are defined, the version
 * of rename() that's used is the POSIX one).  If none of the "major"
 * feature-test macros is defined, _NETBSD_SOURCE is assumed.
 *
 * There are also "minor" feature-test macros, which enable extra
 * functionality in addition to some base standard.  They should be
 * defined along with one of the "major" macros.  The "minor" macros
 * are:
 *
 * _REENTRANT
 * _ISOC99_SOURCE
 * _ISOC11_SOURCE
 * _LARGEFILE_SOURCE            Large File Support
 *              <http://ftp.sas.com/standards/large.file/x_open.20Mar96.html>
 */

#if defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE)
#define _POSIX_C_SOURCE 1L
#endif

#if !defined(_ANSI_SOURCE) && !defined(_POSIX_C_SOURCE) && \
    !defined(_XOPEN_SOURCE) && !defined(_NETBSD_SOURCE)
#define _NETBSD_SOURCE 1
#endif

#if ((_POSIX_C_SOURCE - 0) >= 199506L || (_XOPEN_SOURCE - 0) >= 500) && \
    !defined(_REENTRANT)
#define _REENTRANT
#endif