This is xnu-8019. See this file in:
/*
 * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
 * 
 * @APPLE_LICENSE_HEADER_START@
 * 
 * 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
 */
#include <stdint.h>

/*
 * Format of a symbol table entry of a Mach-O file for 32-bit architectures.
 * 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 a larger
 * number of sections not just the three sections (text, data and bss) in a BSD
 * file.
 */
struct nlist {
	union {
#ifndef __LP64__
		char *n_name;	/* for use when in-core */
#endif
		uint32_t n_strx;	/* index into the string table */
	} n_un;
	uint8_t n_type;		/* type flag, see below */
	uint8_t n_sect;		/* section number or NO_SECT */
	int16_t n_desc;		/* see <mach-o/stab.h> */
	uint32_t n_value;	/* value of this symbol (or stab offset) */
};

/*
 * This is the symbol table entry structure for 64-bit architectures.
 */
struct nlist_64 {
    union {
        uint32_t  n_strx; /* index into the string table */
    } n_un;
    uint8_t n_type;        /* type flag, see below */
    uint8_t n_sect;        /* section number or NO_SECT */
    uint16_t n_desc;       /* see <mach-o/stab.h> */
    uint64_t 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 four 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.  The alignment of a common symbol may be set as a power of 2
 * between 2^1 and 2^15 as part of the n_desc field using the macros below. If
 * the alignment is not set (a value of zero) then natural alignment based on
 * the size is used.
 */
#define GET_COMM_ALIGN(n_desc) (((n_desc) >> 8) & 0x0f)
#define SET_COMM_ALIGN(n_desc,align) \
    (n_desc) = (((n_desc) & 0xf0ff) | (((align) & 0x0f) << 8))

/*
 * 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				0x7
/* 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

/*
 * For images created by the static link editor with the -twolevel_namespace
 * option in effect the flags field of the mach header is marked with
 * MH_TWOLEVEL.  And the binding of the undefined references of the image are
 * determined by the static link editor.  Which library an undefined symbol is
 * bound to is recorded by the static linker in the high 8 bits of the n_desc
 * field using the SET_LIBRARY_ORDINAL macro below.  The ordinal recorded
 * references the libraries listed in the Mach-O's LC_LOAD_DYLIB,
 * LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB, LC_LOAD_UPWARD_DYLIB, and
 * LC_LAZY_LOAD_DYLIB, etc. load commands in the order they appear in the
 * headers.   The library ordinals start from 1.
 * For a dynamic library that is built as a two-level namespace image the
 * undefined references from module defined in another use the same nlist struct
 * an in that case SELF_LIBRARY_ORDINAL is used as the library ordinal.  For
 * defined symbols in all images they also must have the library ordinal set to
 * SELF_LIBRARY_ORDINAL.  The EXECUTABLE_ORDINAL refers to the executable
 * image for references from plugins that refer to the executable that loads
 * them.
 * 
 * The DYNAMIC_LOOKUP_ORDINAL is for undefined symbols in a two-level namespace
 * image that are looked up by the dynamic linker with flat namespace semantics.
 * This ordinal was added as a feature in Mac OS X 10.3 by reducing the
 * value of MAX_LIBRARY_ORDINAL by one.  So it is legal for existing binaries
 * or binaries built with older tools to have 0xfe (254) dynamic libraries.  In
 * this case the ordinal value 0xfe (254) must be treated as a library ordinal
 * for compatibility. 
 */
#define GET_LIBRARY_ORDINAL(n_desc) (((n_desc) >> 8) & 0xff)
#define SET_LIBRARY_ORDINAL(n_desc,ordinal) \
	(n_desc) = (((n_desc) & 0x00ff) | (((ordinal) & 0xff) << 8))
#define SELF_LIBRARY_ORDINAL 0x0
#define MAX_LIBRARY_ORDINAL 0xfd
#define DYNAMIC_LOOKUP_ORDINAL 0xfe
#define EXECUTABLE_ORDINAL 0xff

/*
 * The bit 0x0020 of the n_desc field is used for two non-overlapping purposes
 * and has two different symbolic names, N_NO_DEAD_STRIP and N_DESC_DISCARDED.
 */

/*
 * The N_NO_DEAD_STRIP bit of the n_desc field only ever appears in a 
 * relocatable .o file (MH_OBJECT filetype). And is used to indicate to the
 * static link editor it is never to dead strip the symbol.
 */
#define N_NO_DEAD_STRIP 0x0020 /* symbol is not to be dead stripped */

/*
 * The N_DESC_DISCARDED bit of the n_desc field never appears in linked image.
 * But is used in very rare cases by the dynamic link editor to mark an in
 * memory symbol as discared and longer used for linking.
 */
#define N_DESC_DISCARDED 0x0020	/* symbol is discarded */

/*
 * The N_WEAK_REF bit of the n_desc field indicates to the dynamic linker that
 * the undefined symbol is allowed to be missing and is to have the address of
 * zero when missing.
 */
#define N_WEAK_REF	0x0040 /* symbol is weak referenced */

/*
 * The N_WEAK_DEF bit of the n_desc field indicates to the static and dynamic
 * linkers that the symbol definition is weak, allowing a non-weak symbol to
 * also be used which causes the weak definition to be discared.  Currently this
 * is only supported for symbols in coalesed sections.
 */
#define N_WEAK_DEF	0x0080 /* coalesed symbol is a weak definition */

/*
 * The N_REF_TO_WEAK bit of the n_desc field indicates to the dynamic linker
 * that the undefined symbol should be resolved using flat namespace searching.
 */
#define	N_REF_TO_WEAK	0x0080 /* reference to a weak symbol */

/*
 * The N_ARM_THUMB_DEF bit of the n_desc field indicates that the symbol is
 * a defintion of a Thumb function.
 */
#define N_ARM_THUMB_DEF	0x0008 /* symbol is a Thumb function (ARM) */

/*
 * The N_SYMBOL_RESOLVER bit of the n_desc field indicates that the
 * that the function is actually a resolver function and should
 * be called to get the address of the real function to use.
 * This bit is only available in .o files (MH_OBJECT filetype)
 */
#define N_SYMBOL_RESOLVER  0x0100 

/*
 * The N_ALT_ENTRY bit of the n_desc field indicates that the
 * symbol is pinned to the previous content.
 */
#define N_ALT_ENTRY 0x0200

#ifndef __STRICT_BSD__
#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
/*
 * The function nlist(3) from the C library.
 */
extern int nlist (const char *filename, struct nlist *list);
#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif /* __STRICT_BSD__ */

#endif /* _MACHO_LIST_H_ */