dl-librecon.h

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Optional code to distinguish library flavours.
   Copyright (C) 1998, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail]>, 1998.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifndef _DL_LIBRECON_H

#include <sysdeps/unix/sysv/linux/dl-librecon.h>

#define DISTINGUISH_LIB_VERSIONS \
  do									      \
    {									      \
      /* We have to find out whether the binary is linked against	      \
	 libc 5 or glibc.  We do this by looking at all the DT_NEEDED	      \
	 entries.  If one is libc.so.5 this is a libc 5 linked binary.  */    \
      if (main_map->l_info[DT_NEEDED])					      \
	{								      \
	  /* We have dependencies.  */					      \
	  const ElfW(Dyn) *d;						      \
	  const char *strtab;						      \
									      \
	  strtab = (const char *) D_PTR (main_map, l_info[DT_STRTAB]);	      \
									      \
	  for (d = main_map->l_ld; d->d_tag != DT_NULL; ++d)		      \
	    if (d->d_tag == DT_NEEDED					      \
		&& strcmp (strtab + d->d_un.d_val, "libc.so.5") == 0)	      \
	      break;							      \
									      \
	  /* We print a `5' or `6' depending on the outcome.  */	      \
	  _dl_printf (d->d_tag != DT_NULL ? "5\n" : "6\n");		      \
	}								      \
    }									      \
  while (0)

/* Recognizing extra environment variables.  */
#define EXTRA_LD_ENVVARS \
  case 15:								      \
    if (memcmp (envline, "LIBRARY_VERSION", 15) == 0)			      \
      GLRO(dl_correct_cache_id) = envline[16] == '5' ? 2 : 3;		      \
    break;								      \

/* Extra unsecure variables.  The names are all stuffed in a single
   string which means they have to be terminated with a '\0' explicitly.  */
#define EXTRA_UNSECURE_ENVVARS \
  "LD_AOUT_LIBRARY_PATH\0"						      \
  "LD_AOUT_PRELOAD\0"

#endif /* dl-librecon.h */