[Bug math/13268] New: modf, modff, modfl: help GCC with argument checking

["bruno at clisp dot org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13268

             Bug #: 13268
           Summary: modf, modff, modfl: help GCC with argument checking
           Product: glibc
           Version: 2.11
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: aj@suse.de
        ReportedBy: bruno@clisp.org
    Classification: Unclassified


The second argument of the functions modf, modff, modfl must not be a NULL
pointer, according to POSIX, and the glibc implementation also does not allow
a NULL pointer.

It would be useful to allow GCC to give a warning when someone passes a NULL
literal to these functions.

How to reproduce:
==================== foo.c ========================
#include <math.h>
#include <stddef.h>
int
main ()
{
  return ! modf (2.4, NULL);
}
===================================================
$ gcc -Wall foo.c

Expected result:
foo.c: In function 'main':
foo.c:6:3: warning: null argument where non-null required (argument 2)

Actual result:
No diagnostic.

The fix should be easy: Add a properly conditionalized
__attribute__ ((__nonnull__ (2)))
to glibc/math/bits/mathcalls.h line 116.

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