FreeBSD/Linux Kernel Cross Reference
sys/EXTERNAL_HEADERS/mach-o/nlist.h

     /*
      * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
      *
      * @APPLE_LICENSE_HEADER_START@
      * 
      * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
      * 
      * This file contains Original Code and/or Modifications of Original Code
      * as defined in and that are subject to the Apple Public Source License
     * Version 2.0 (the 'License'). You may not use this file except in
     * compliance with the License. Please obtain a copy of the License at
     * http://www.opensource.apple.com/apsl/ and read it before using this
     * file.
     * 
     * The Original Code and all software distributed under the License are
     * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
     * Please see the License for the specific language governing rights and
     * limitations under the License.
     * 
     * @APPLE_LICENSE_HEADER_END@
     */
    #ifndef _MACHO_NLIST_H_
    #define _MACHO_NLIST_H_
    /*      $NetBSD: nlist.h,v 1.5 1994/10/26 00:56:11 cgd Exp $    */
    
    /*-
     * Copyright (c) 1991, 1993
     *      The Regents of the University of California.  All rights reserved.
     * (c) UNIX System Laboratories, Inc.
     * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)nlist.h     8.2 (Berkeley) 1/21/94
     */
    
    /*
     * Format of a symbol table entry of a Mach-O file.  Modified from the BSD
     * format.  The modifications from the original format were changing n_other
     * (an unused field) to n_sect and the addition of the N_SECT type.  These
     * modifications are required to support symbols in an arbitrary number of
     * sections not just the three sections (text, data and bss) in a BSD file.
     */
    struct nlist {
            union {
                    char *n_name;   /* for use when in-core */
                    long  n_strx;   /* index into the string table */
            } n_un;
            unsigned char n_type;   /* type flag, see below */
            unsigned char n_sect;   /* section number or NO_SECT */
            short         n_desc;   /* see <mach-o/stab.h> */
            unsigned long n_value;  /* value of this symbol (or stab offset) */
    };
    
    /*
     * Symbols with a index into the string table of zero (n_un.n_strx == 0) are
     * defined to have a null, "", name.  Therefore all string indexes to non null
     * names must not have a zero string index.  This is bit historical information
     * that has never been well documented.
     */
    
    /*
     * The n_type field really contains three fields:
     *      unsigned char N_STAB:3,
     *                    N_PEXT:1,
     *                    N_TYPE:3,
     *                    N_EXT:1;
    * which are used via the following masks.
    */
   #define N_STAB  0xe0  /* if any of these bits set, a symbolic debugging entry */
   #define N_PEXT  0x10  /* private external symbol bit */
   #define N_TYPE  0x0e  /* mask for the type bits */
   #define N_EXT   0x01  /* external symbol bit, set for external symbols */
   
   /*
    * Only symbolic debugging entries have some of the N_STAB bits set and if any
    * of these bits are set then it is a symbolic debugging entry (a stab).  In
    * which case then the values of the n_type field (the entire field) are given
    * in <mach-o/stab.h>
    */
   
   /*
    * Values for N_TYPE bits of the n_type field.
    */
   #define N_UNDF  0x0             /* undefined, n_sect == NO_SECT */
   #define N_ABS   0x2             /* absolute, n_sect == NO_SECT */
   #define N_SECT  0xe             /* defined in section number n_sect */
   #define N_PBUD  0xc             /* prebound undefined (defined in a dylib) */
   #define N_INDR  0xa             /* indirect */
   
   /* 
    * If the type is N_INDR then the symbol is defined to be the same as another
    * symbol.  In this case the n_value field is an index into the string table
    * of the other symbol's name.  When the other symbol is defined then they both
    * take on the defined type and value.
    */
   
   /*
    * If the type is N_SECT then the n_sect field contains an ordinal of the
    * section the symbol is defined in.  The sections are numbered from 1 and 
    * refer to sections in order they appear in the load commands for the file
    * they are in.  This means the same ordinal may very well refer to different
    * sections in different files.
    *
    * The n_value field for all symbol table entries (including N_STAB's) gets
    * updated by the link editor based on the value of it's n_sect field and where
    * the section n_sect references gets relocated.  If the value of the n_sect 
    * field is NO_SECT then it's n_value field is not changed by the link editor.
    */
   #define NO_SECT         0       /* symbol is not in any section */
   #define MAX_SECT        255     /* 1 thru 255 inclusive */
   
   /*
    * Common symbols are represented by undefined (N_UNDF) external (N_EXT) types
    * who's values (n_value) are non-zero.  In which case the value of the n_value
    * field is the size (in bytes) of the common symbol.  The n_sect field is set
    * to NO_SECT.
    */
   
   /*
    * To support the lazy binding of undefined symbols in the dynamic link-editor,
    * the undefined symbols in the symbol table (the nlist structures) are marked
    * with the indication if the undefined reference is a lazy reference or
    * non-lazy reference.  If both a non-lazy reference and a lazy reference is
    * made to the same symbol the non-lazy reference takes precedence.  A reference
    * is lazy only when all references to that symbol are made through a symbol
    * pointer in a lazy symbol pointer section.
    *
    * The implementation of marking nlist structures in the symbol table for
    * undefined symbols will be to use some of the bits of the n_desc field as a
    * reference type.  The mask REFERENCE_TYPE will be applied to the n_desc field
    * of an nlist structure for an undefined symbol to determine the type of
    * undefined reference (lazy or non-lazy).
    *
    * The constants for the REFERENCE FLAGS are propagated to the reference table
    * in a shared library file.  In that case the constant for a defined symbol,
    * REFERENCE_FLAG_DEFINED, is also used.
    */
   /* Reference type bits of the n_desc field of undefined symbols */
   #define REFERENCE_TYPE                          0xf
   /* types of references */
   #define REFERENCE_FLAG_UNDEFINED_NON_LAZY               0
   #define REFERENCE_FLAG_UNDEFINED_LAZY                   1
   #define REFERENCE_FLAG_DEFINED                          2
   #define REFERENCE_FLAG_PRIVATE_DEFINED                  3
   #define REFERENCE_FLAG_PRIVATE_UNDEFINED_NON_LAZY       4
   #define REFERENCE_FLAG_PRIVATE_UNDEFINED_LAZY           5
   
   /*
    * To simplify stripping of objects that use are used with the dynamic link
    * editor, the static link editor marks the symbols defined an object that are
    * referenced by a dynamicly bound object (dynamic shared libraries, bundles).
    * With this marking strip knows not to strip these symbols.
    */
   #define REFERENCED_DYNAMICALLY  0x0010
   
   /*
    * The non-reference type bits of the n_desc field for global symbols are
    * reserved for the dynamic link editor.  All of these bits must start out
    * zero in the object file.
    */
   #define N_DESC_DISCARDED 0x8000 /* symbol is discarded */
   
   #endif

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