1/*
2 * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
3 *
4 * @APPLE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. Please obtain a copy of the License at
10 * http://www.opensource.apple.com/apsl/ and read it before using this
11 * file.
12 *
13 * The Original Code and all software distributed under the License are
14 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
15 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
16 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
18 * Please see the License for the specific language governing rights and
19 * limitations under the License.
20 *
21 * @APPLE_LICENSE_HEADER_END@
22 */
23/* $NetBSD: exec.h,v 1.6 1994/10/27 04:16:05 cgd Exp $ */
24
25/*
26 * Copyright (c) 1993 Christopher G. Demetriou
27 * All rights reserved.
28 *
29 * Redistribution and use in source and binary forms, with or without
30 * modification, are permitted provided that the following conditions
31 * are met:
32 * 1. Redistributions of source code must retain the above copyright
33 * notice, this list of conditions and the following disclaimer.
34 * 2. Redistributions in binary form must reproduce the above copyright
35 * notice, this list of conditions and the following disclaimer in the
36 * documentation and/or other materials provided with the distribution.
37 * 3. The name of the author may not be used to endorse or promote products
38 * derived from this software without specific prior written permission
39 *
40 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
41 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
42 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
43 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
44 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
45 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
46 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
47 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
48 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
49 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
50 */
51
52#ifndef _MACHO_RELOC_H_
53#define _MACHO_RELOC_H_
54#include <stdint.h>
55
56/*
57 * Format of a relocation entry of a Mach-O file. Modified from the 4.3BSD
58 * format. The modifications from the original format were changing the value
59 * of the r_symbolnum field for "local" (r_extern == 0) relocation entries.
60 * This modification is required to support symbols in an arbitrary number of
61 * sections not just the three sections (text, data and bss) in a 4.3BSD file.
62 * Also the last 4 bits have had the r_type tag added to them.
63 */
64struct relocation_info {
65 int32_t r_address; /* offset in the section to what is being
66 relocated */
67 uint32_t r_symbolnum:24, /* symbol index if r_extern == 1 or section
68 ordinal if r_extern == 0 */
69 r_pcrel:1, /* was relocated pc relative already */
70 r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
71 r_extern:1, /* does not include value of sym referenced */
72 r_type:4; /* if not 0, machine specific relocation type */
73};
74#define R_ABS 0 /* absolute relocation type for Mach-O files */
75
76/*
77 * The r_address is not really the address as it's name indicates but an offset.
78 * In 4.3BSD a.out objects this offset is from the start of the "segment" for
79 * which relocation entry is for (text or data). For Mach-O object files it is
80 * also an offset but from the start of the "section" for which the relocation
81 * entry is for. See comments in <mach-o/loader.h> about the r_address feild
82 * in images for used with the dynamic linker.
83 *
84 * In 4.3BSD a.out objects if r_extern is zero then r_symbolnum is an ordinal
85 * for the segment the symbol being relocated is in. These ordinals are the
86 * symbol types N_TEXT, N_DATA, N_BSS or N_ABS. In Mach-O object files these
87 * ordinals refer to the sections in the object file in the order their section
88 * structures appear in the headers of the object file they are in. The first
89 * section has the ordinal 1, the second 2, and so on. This means that the
90 * same ordinal in two different object files could refer to two different
91 * sections. And further could have still different ordinals when combined
92 * by the link-editor. The value R_ABS is used for relocation entries for
93 * absolute symbols which need no further relocation.
94 */
95
96/*
97 * For RISC machines some of the references are split across two instructions
98 * and the instruction does not contain the complete value of the reference.
99 * In these cases a second, or paired relocation entry, follows each of these
100 * relocation entries, using a PAIR r_type, which contains the other part of the
101 * reference not contained in the instruction. This other part is stored in the
102 * pair's r_address field. The exact number of bits of the other part of the
103 * reference store in the r_address field is dependent on the particular
104 * relocation type for the particular architecture.
105 */
106
107/*
108 * To make scattered loading by the link editor work correctly "local"
109 * relocation entries can't be used when the item to be relocated is the value
110 * of a symbol plus an offset (where the resulting expresion is outside the
111 * block the link editor is moving, a blocks are divided at symbol addresses).
112 * In this case. where the item is a symbol value plus offset, the link editor
113 * needs to know more than just the section the symbol was defined. What is
114 * needed is the actual value of the symbol without the offset so it can do the
115 * relocation correctly based on where the value of the symbol got relocated to
116 * not the value of the expression (with the offset added to the symbol value).
117 * So for the NeXT 2.0 release no "local" relocation entries are ever used when
118 * there is a non-zero offset added to a symbol. The "external" and "local"
119 * relocation entries remain unchanged.
120 *
121 * The implemention is quite messy given the compatibility with the existing
122 * relocation entry format. The ASSUMPTION is that a section will never be
123 * bigger than 2**24 - 1 (0x00ffffff or 16,777,215) bytes. This assumption
124 * allows the r_address (which is really an offset) to fit in 24 bits and high
125 * bit of the r_address field in the relocation_info structure to indicate
126 * it is really a scattered_relocation_info structure. Since these are only
127 * used in places where "local" relocation entries are used and not where
128 * "external" relocation entries are used the r_extern field has been removed.
129 *
130 * For scattered loading to work on a RISC machine where some of the references
131 * are split across two instructions the link editor needs to be assured that
132 * each reference has a unique 32 bit reference (that more than one reference is
133 * NOT sharing the same high 16 bits for example) so it move each referenced
134 * item independent of each other. Some compilers guarantees this but the
135 * compilers don't so scattered loading can be done on those that do guarantee
136 * this.
137 */
138#if defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__)
139/*
140 * The reason for the ifdef's of __BIG_ENDIAN__ and __LITTLE_ENDIAN__ are that
141 * when stattered relocation entries were added the mistake of using a mask
142 * against a structure that is made up of bit fields was used. To make this
143 * design work this structure must be laid out in memory the same way so the
144 * mask can be applied can check the same bit each time (r_scattered).
145 */
146#endif /* defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__) */
147#define R_SCATTERED 0x80000000 /* mask to be applied to the r_address field
148 of a relocation_info structure to tell that
149 is is really a scattered_relocation_info
150 stucture */
151struct scattered_relocation_info {
152#ifdef __BIG_ENDIAN__
153 uint32_t r_scattered:1, /* 1=scattered, 0=non-scattered (see above) */
154 r_pcrel:1, /* was relocated pc relative already */
155 r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
156 r_type:4, /* if not 0, machine specific relocation type */
157 r_address:24; /* offset in the section to what is being
158 relocated */
159 int32_t r_value; /* the value the item to be relocated is
160 refering to (without any offset added) */
161#endif /* __BIG_ENDIAN__ */
162#ifdef __LITTLE_ENDIAN__
163 uint32_t
164 r_address:24, /* offset in the section to what is being
165 relocated */
166 r_type:4, /* if not 0, machine specific relocation type */
167 r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
168 r_pcrel:1, /* was relocated pc relative already */
169 r_scattered:1; /* 1=scattered, 0=non-scattered (see above) */
170 int32_t r_value; /* the value the item to be relocated is
171 refering to (without any offset added) */
172#endif /* __LITTLE_ENDIAN__ */
173};
174
175/*
176 * Relocation types used in a generic implementation. Relocation entries for
177 * normal things use the generic relocation as discribed above and their r_type
178 * is GENERIC_RELOC_VANILLA (a value of zero).
179 *
180 * Another type of generic relocation, GENERIC_RELOC_SECTDIFF, is to support
181 * the difference of two symbols defined in different sections. That is the
182 * expression "symbol1 - symbol2 + constant" is a relocatable expression when
183 * both symbols are defined in some section. For this type of relocation the
184 * both relocations entries are scattered relocation entries. The value of
185 * symbol1 is stored in the first relocation entry's r_value field and the
186 * value of symbol2 is stored in the pair's r_value field.
187 *
188 * A special case for a prebound lazy pointer is needed to beable to set the
189 * value of the lazy pointer back to its non-prebound state. This is done
190 * using the GENERIC_RELOC_PB_LA_PTR r_type. This is a scattered relocation
191 * entry where the r_value feild is the value of the lazy pointer not prebound.
192 */
193enum reloc_type_generic
194{
195 GENERIC_RELOC_VANILLA, /* generic relocation as discribed above */
196 GENERIC_RELOC_PAIR, /* Only follows a GENERIC_RELOC_SECTDIFF */
197 GENERIC_RELOC_SECTDIFF,
198 GENERIC_RELOC_PB_LA_PTR, /* prebound lazy pointer */
199 GENERIC_RELOC_LOCAL_SECTDIFF,
200 GENERIC_RELOC_TLV /* thread local variables */
201};
202
203#endif /* _MACHO_RELOC_H_ */
204