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Annotation of GNUtools/cctools/include/mach-o/nlist.h, revision 1.1

1.1     ! root        1: #ifndef _MACHO_NLIST_H_
        !             2: #define _MACHO_NLIST_H_
        !             3: /*
        !             4:  * Copyright (c) 1980 Regents of the University of California.
        !             5:  * All rights reserved.  The Berkeley software License Agreement
        !             6:  * specifies the terms and conditions for redistribution.
        !             7:  *
        !             8:  *     @(#)nlist.h     5.1 (Berkeley) 5/30/85
        !             9:  */
        !            10: 
        !            11: /*
        !            12:  * Format of a symbol table entry of a Mach-O file.  Modified from the 4.3BSD
        !            13:  * format.  The modifications from the original format were changing n_other
        !            14:  * (an unused field) to n_sect and the addition of the N_SECT type.  These
        !            15:  * modifications are required to support symbols in an arbitrary number of
        !            16:  * sections not just the three sections (text, data and bss) in a 4.3BSD file.
        !            17:  */
        !            18: struct nlist {
        !            19:        union {
        !            20:                char *n_name;   /* for use when in-core */
        !            21:                long  n_strx;   /* index into the string table */
        !            22:        } n_un;
        !            23:        unsigned char n_type;   /* type flag, see below */
        !            24:        unsigned char n_sect;   /* section number or NO_SECT */
        !            25:        short         n_desc;   /* see <mach-o/stab.h> */
        !            26:        unsigned long n_value;  /* value of this symbol (or stab offset) */
        !            27: };
        !            28: 
        !            29: /*
        !            30:  * Symbols with a index into the string table of zero (n_un.n_strx == 0) are
        !            31:  * defined to have a null, "", name.  Therefore all string indexes to non null
        !            32:  * names must not have a zero string index.  This is bit historical information
        !            33:  * that has never been well documented.
        !            34:  */
        !            35: 
        !            36: /*
        !            37:  * The n_type field really contains three fields:
        !            38:  *     unsigned char N_STAB:3,
        !            39:  *                   N_PEXT:1,
        !            40:  *                   N_TYPE:3,
        !            41:  *                   N_EXT:1;
        !            42:  * which are used via the following masks.
        !            43:  */
        !            44: #define        N_STAB  0xe0  /* if any of these bits set, a symbolic debugging entry */
        !            45: #define        N_PEXT  0x10  /* private external symbol bit */
        !            46: #define        N_TYPE  0x0e  /* mask for the type bits */
        !            47: #define        N_EXT   0x01  /* external symbol bit, set for external symbols */
        !            48: 
        !            49: /*
        !            50:  * Only symbolic debugging entries have some of the N_STAB bits set and if any
        !            51:  * of these bits are set then it is a symbolic debugging entry (a stab).  In
        !            52:  * which case then the values of the n_type field (the entire field) are given
        !            53:  * in <mach-o/stab.h>
        !            54:  */
        !            55: 
        !            56: /*
        !            57:  * Values for N_TYPE bits of the n_type field.
        !            58:  */
        !            59: #define        N_UNDF  0x0             /* undefined, n_sect == NO_SECT */
        !            60: #define        N_ABS   0x2             /* absolute, n_sect == NO_SECT */
        !            61: #define        N_SECT  0xe             /* defined in section number n_sect */
        !            62: #define N_INDR 0xa             /* indirect */
        !            63: 
        !            64: /* 
        !            65:  * If the type is N_INDR then the symbol is defined to be the same as another
        !            66:  * symbol.  In this case the n_value field is an index into the string table
        !            67:  * of the other symbol's name.  When the other symbol is defined then they both
        !            68:  * take on the defined type and value.
        !            69:  */
        !            70: 
        !            71: /*
        !            72:  * If the type is N_SECT then the n_sect field contains an ordinal of the
        !            73:  * section the symbol is defined in.  The sections are numbered from 1 and 
        !            74:  * refer to sections in order they appear in the load commands for the file
        !            75:  * they are in.  This means the same ordinal may very well refer to different
        !            76:  * sections in different files.
        !            77:  *
        !            78:  * The n_value field for all symbol table entries (including N_STAB's) gets
        !            79:  * updated by the link editor based on the value of it's n_sect field and where
        !            80:  * the section n_sect references gets relocated.  If the value of the n_sect 
        !            81:  * field is NO_SECT then it's n_value field is not changed by the link editor.
        !            82:  */
        !            83: #define        NO_SECT         0       /* symbol is not in any section */
        !            84: #define MAX_SECT       255     /* 1 thru 255 inclusive */
        !            85: 
        !            86: /*
        !            87:  * Common symbols are represented by undefined (N_UNDF) external (N_EXT) types
        !            88:  * who's values (n_value) are non-zero.  In which case the value of the n_value
        !            89:  * field is the size (in bytes) of the common symbol.  The n_sect field is set
        !            90:  * to NO_SECT.
        !            91:  */
        !            92: 
        !            93: /*
        !            94:  * To support the lazy binding of undefined symbols in the dynamic link-editor,
        !            95:  * the undefined symbols in the symbol table (the nlist structures) are marked
        !            96:  * with the indication if the undefined reference is a lazy reference or
        !            97:  * non-lazy reference.  If both a non-lazy reference and a lazy reference is
        !            98:  * made to the same symbol the non-lazy reference takes precedence.  A reference
        !            99:  * is lazy only when all references to that symbol are made through a symbol
        !           100:  * pointer in a lazy symbol pointer section.
        !           101:  *
        !           102:  * The implementation of marking nlist structures in the symbol table for
        !           103:  * undefined symbols will be to use some of the bits of the n_desc field as a
        !           104:  * reference type.  The mask REFERENCE_TYPE will be applied to the n_desc field
        !           105:  * of an nlist structure for an undefined symbol to determine the type of
        !           106:  * undefined reference (lazy or non-lazy).
        !           107:  *
        !           108:  * The constants for the REFERENCE FLAGS are propagated to the reference table
        !           109:  * in a shared library file.  In that case the constant for a defined symbol,
        !           110:  * REFERENCE_FLAG_DEFINED, is also used.
        !           111:  */
        !           112: /* Reference type bits of the n_desc field of undefined symbols */
        !           113: #define REFERENCE_TYPE                         0xff
        !           114: /* types of references */
        !           115: #define REFERENCE_FLAG_UNDEFINED_NON_LAZY              0
        !           116: #define REFERENCE_FLAG_UNDEFINED_LAZY                  1
        !           117: #define REFERENCE_FLAG_DEFINED                         2
        !           118: #define REFERENCE_FLAG_PRIVATE_DEFINED                 3
        !           119: #define REFERENCE_FLAG_PRIVATE_UNDEFINED_NON_LAZY      4
        !           120: #define REFERENCE_FLAG_PRIVATE_UNDEFINED_LAZY          5
        !           121: 
        !           122: #ifndef __STRICT_BSD__
        !           123: /*
        !           124:  * The function nlist(3) from the C library.
        !           125:  */
        !           126: extern int nlist (const char *filename, struct nlist *list);
        !           127: #endif __STRICT_BSD__
        !           128: 
        !           129: #endif _MACHO_LIST_H_

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