Moving (initially function) attribute macros into a separate gnulib module

[James Youngman]

I just went to use some function attributes in findutils and noticed
that information about which versions of GCC support various
attributes is spread throughout gnulib.  While a number of headers
define convenience macros (usually starting _GL_ATTRIBUTE_) there are
a couple of naming inconsistencies (two names used for the same
attribute, typically).

I propose to move all of these definitions into a separate module,
except for any definitions that need to stay as they are in order to
stay in sync with glibc:

$ for h in $(grep -l 'define.*_GL_ATTRIBUTE' lib/*.[hc]) ; do grep -q
'This file is part of the GNU C Library' $h || echo $h; done
lib/di-set.h
lib/hash.h
lib/ignore-value.h
lib/ino-map.h
lib/openat.h
lib/safe-alloc.h
lib/sigpipe-die.h
lib/stdio.in.h
lib/stdlib.in.h
lib/string.in.h
lib/vasnprintf.h
lib/version-etc.h
lib/xalloc.h
lib/xmemdup0.h
lib/xprintf.h
lib/xstrtol.h
lib/xvasprintf.h

Since this involves touching a number of files, I thought it would be
useful to get some feedback on the idea in advance rather than just
send a patch for review.

In particular, if we keep the existing macro naming, I think the
change would need to be one large patch, because many of the existing
definitions of these macros are not protected by #ifndef.  If it's not
done in one large patch, differences in header inclusion order will
mean that we'd see extra warnings about "redefinition of
_GL_ATTRIBUTE_NORETURN" etc. when compiling gnulib code.

While the hard work is updating all the other source files, here's an
initial version of the definitions themselves, in case this helps
better convey the idea:


/* gcc-function-attribtues.h -- GCC-specific function attributes

   Copyright (C) 2011 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/*
 Be aware that some function attributes do not work with function
 pointers.  See
 http://lists.gnu.org/archive/html/bug-gnulib/2011-04/msg00007.html
 for details.
*/
#ifndef _GCC_FUNCTION_ATTRIBUTES_H
#define _GCC_FUNCTION_ATTRIBUTES_H

#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

/*
The following attributes are currently (GCC-4.4.5) defined for
functions on all targets.  Where this file provides a macro
for using it, the macro name is given in the second column.

Attribute                 Macro (if implemented in this file)
-------------------------------------------------------------------------------
alias
aligned
alloc_size                _GL_ATTRIBUTE_ALLOC_SIZE(arg_num)
always_inline
artificial
cold
const
constructor
deprecated                _GL_ATTRIBUTE_DEPRECATED
destructor
error
externally_visible
flatten
format                    _GL_ATTRIBUTE_FORMAT(spec)
                          _GL_ATTRIBUTE_FORMAT_PRINTF_SYSTEM(fmt,firstarg)
                          _GL_ATTRIBUTE_FORMAT_PRINTF(fmt,firstarg)
                          _GL_ATTRIBUTE_FORMAT_SCANF_SYSTEM(fmt,firstarg)
                          _GL_ATTRIBUTE_FORMAT_SCANF(fmt,firstarg)
format_arg
gnu_inline
hot
malloc                    _GL_ATTRIBUTE_MALLOC
no_instrument_function
noinline
nonnull                   _GL_ATTRIBUTE_NONNULL(args)
                          _GL_ARG_NONNULL(args)
noreturn                  _GL_ATTRIBUTE_NORETURN
nothrow
pure                      _GL_ATTRIBUTE_PURE
returns_twice
section
sentinel                  _GL_ATTRIBUTE_SENTINEL
unused
used
warn_unused_result        _GL_ATTRIBUTE_WUR
warning
weak
*/

/*
Attributes used in gnulib, but which appear to be platform-specific
regparm
stdcall
*/

/*
Attributes used in gnulib with special arguments
Macro         Args
visibility    "default"
*/

/*
   The __attribute__ feature is available in gcc versions 2.5 and later.
   The underscored __format__ spelling of the attribute names requires
2.6.4 (we check for 2.7).
*/


#ifndef _GL_ATTRIBUTE_ALLOC_SIZE
# if __GNUC_PREREQ(4,3)
#  define _GL_ATTRIBUTE_ALLOC_SIZE(arg_num) __attribute__
((__alloc_size__ (arg_num)))
# else
#  define _GL_ATTRIBUTE_ALLOC_SIZE(arg_num) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_DEPRECATED
# if __GNUC_PREREQ(3,1)
#  define _GL_ATTRIBUTE_DEPRECATED __attribute__ ((__deprecated__))
# else
#  define _GL_ATTRIBUTE_DEPRECATED /* empty */
# endif
#endif

#ifndef _GL_ATTRIBUTE_FORMAT
# if __GNUC_PREREQ(2,7)
#  define _GL_ATTRIBUTE_FORMAT(spec)  __attribute__ ((__format__ spec))
# else
#  define _GL_ATTRIBUTE_FORMAT(spec) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_FORMAT_PRINTF_SYSTEM
# if __GNUC_PREREQ(2,7)
#  define _GL_ATTRIBUTE_FORMAT_PRINTF_SYSTEM(formatstring_parameter,
first_argument) \
    _GL_ATTRIBUTE_FORMAT ((__printf__, formatstring_parameter, first_argument))
# else
#  define _GL_ATTRIBUTE_FORMAT_PRINTF_SYSTEM(spec) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_FORMAT_PRINTF
# if __GNUC_PREREQ(2,7)
#  if __GNUC_PREREQ(4,4)
#   define _GL_ATTRIBUTE_FORMAT_PRINTF(formatstring_parameter, first_argument) \
     _GL_ATTRIBUTE_FORMAT ((__gnu_printf__, formatstring_parameter,
first_argument))
#  else
#   define _GL_ATTRIBUTE_FORMAT_PRINTF(formatstring_parameter, first_argument) \
     _GL_ATTRIBUTE_FORMAT ((__printf__, formatstring_parameter, first_argument))
#  endif
# else
#  define _GL_ATTRIBUTE_FORMAT_PRINTF(spec) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_FORMAT_SCANF_SYSTEM
# if __GNUC_PREREQ(2,7)
#  define _GL_ATTRIBUTE_FORMAT_SCANF_SYSTEM(formatstring_parameter,
first_argument) \
    _GL_ATTRIBUTE_FORMAT ((__scanf__, formatstring_parameter, first_argument))
# else
#  define _GL_ATTRIBUTE_FORMAT_SCANF_SYSTEM(spec) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_FORMAT_SCANF
# if __GNUC_PREREQ(2,7)
#  if __GNUC_PREREQ(4,4)
#   define _GL_ATTRIBUTE_FORMAT_SCANF(formatstring_parameter, first_argument) \
     _GL_ATTRIBUTE_FORMAT ((__gnu_scanf__, formatstring_parameter,
first_argument))
#  else
#   define _GL_ATTRIBUTE_FORMAT_SCANF(formatstring_parameter, first_argument) \
     _GL_ATTRIBUTE_FORMAT ((__scanf__, formatstring_parameter, first_argument))
#  endif
# else
#  define _GL_ATTRIBUTE_FORMAT_SCANF(spec) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_MALLOC
# if __GNUC_PREREQ(3,0)
#  define _GL_ATTRIBUTE_MALLOC __attribute__ ((__malloc__))
# else
#  define _GL_ATTRIBUTE_MALLOC /* unsupported */
# endif
#endif


#ifndef _GL_ATTRIBUTE_NONNULL
# if __GNUC_PREREQ(3,3)
#   define _GL_ATTRIBUTE_NONNULL(m) __attribute__ ((__nonnull__ (m)))
#  else
#   define _GL_ATTRIBUTE_NONNULL(m) /* unsupported */
# endif
#endif
#ifndef _GL_ARG_NONNULL
/* alternative spelling used in gnulib's stdio.h */
# define _GL_ARG_NONNULL(m) _GL_ATTRIBUTE_NONNULL(m)
#endif


#ifndef _GL_ATTRIBUTE_NORETURN
# if __GNUC_PREREQ(2,8)
#   define _GL_ATTRIBUTE_NORETURN __attribute__ ((__noreturn__ (m)))
#  else
#   define _GL_ATTRIBUTE_NORETURN /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_PURE
# if __GNUC_PREREQ(2,96)
#   define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__))
#  else
#   define _GL_ATTRIBUTE_PURE /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_SENTINEL
# if __GNUC_PREREQ(4,0)
  /* gnulib uses the __attribute__((__sentinel__)) variant, for which the
    argument number 0 is assumed.  Arguments are counted backwards, the last
    being 0.
  */
#   define _GL_ATTRIBUTE_SENTINEL(backward_arg_num) __attribute__
((__sentinel__(backward_arg_num)))
#  else
#   define _GL_ATTRIBUTE_SENTINEL(backward_arg_num) /* unsupported */
# endif
#endif

#ifndef _GL_ATTRIBUTE_WUR
# if __GNUC_PREREQ(3,4)
#  define _GL_ATTRIBUTE_WUR __attribute__ ((__warn__unused_result__))
# else
#  define _GL_ATTRIBUTE_WUR /* unsupported */
# endif
#endif
#ifndef _GL_ATTRIBUTE_RETURN_CHECK
/* gnulib is inconsistent in which macro it uses; support both for now. */
# define _GL_ATTRIBUTE_RETURN_CHECK _GL_ATTRIBUTE_WUR
#endif

#endif /* _GCC_FUNCTION_ATTRIBUTES_H */