reloc.h
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 */ 64 struct 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 */ 151 struct 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 */ 193 enum 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_ */