/* * Copyright (c) 1999 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@ */ /* $NetBSD: exec.h,v 1.6 1994/10/27 04:16:05 cgd Exp $ */ /* * Copyright (c) 1993 Christopher G. Demetriou * All rights reserved. * * 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. The name of the author may not be used to endorse or promote products * derived from this software without specific prior written permission * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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. */ #ifndef _MACHO_RELOC_H_ #define _MACHO_RELOC_H_ #include /* * Format of a relocation entry of a Mach-O file. Modified from the 4.3BSD * format. The modifications from the original format were changing the value * of the r_symbolnum field for "local" (r_extern == 0) relocation entries. * This modification is required to support symbols in an arbitrary number of * sections not just the three sections (text, data and bss) in a 4.3BSD file. * Also the last 4 bits have had the r_type tag added to them. */ struct relocation_info { int32_t r_address; /* offset in the section to what is being relocated */ uint32_t r_symbolnum:24, /* symbol index if r_extern == 1 or section ordinal if r_extern == 0 */ r_pcrel:1, /* was relocated pc relative already */ r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */ r_extern:1, /* does not include value of sym referenced */ r_type:4; /* if not 0, machine specific relocation type */ }; #define R_ABS 0 /* absolute relocation type for Mach-O files */ /* * The r_address is not really the address as it's name indicates but an offset. * In 4.3BSD a.out objects this offset is from the start of the "segment" for * which relocation entry is for (text or data). For Mach-O object files it is * also an offset but from the start of the "section" for which the relocation * entry is for. See comments in about the r_address feild * in images for used with the dynamic linker. * * In 4.3BSD a.out objects if r_extern is zero then r_symbolnum is an ordinal * for the segment the symbol being relocated is in. These ordinals are the * symbol types N_TEXT, N_DATA, N_BSS or N_ABS. In Mach-O object files these * ordinals refer to the sections in the object file in the order their section * structures appear in the headers of the object file they are in. The first * section has the ordinal 1, the second 2, and so on. This means that the * same ordinal in two different object files could refer to two different * sections. And further could have still different ordinals when combined * by the link-editor. The value R_ABS is used for relocation entries for * absolute symbols which need no further relocation. */ /* * For RISC machines some of the references are split across two instructions * and the instruction does not contain the complete value of the reference. * In these cases a second, or paired relocation entry, follows each of these * relocation entries, using a PAIR r_type, which contains the other part of the * reference not contained in the instruction. This other part is stored in the * pair's r_address field. The exact number of bits of the other part of the * reference store in the r_address field is dependent on the particular * relocation type for the particular architecture. */ /* * To make scattered loading by the link editor work correctly "local" * relocation entries can't be used when the item to be relocated is the value * of a symbol plus an offset (where the resulting expresion is outside the * block the link editor is moving, a blocks are divided at symbol addresses). * In this case. where the item is a symbol value plus offset, the link editor * needs to know more than just the section the symbol was defined. What is * needed is the actual value of the symbol without the offset so it can do the * relocation correctly based on where the value of the symbol got relocated to * not the value of the expression (with the offset added to the symbol value). * So for the NeXT 2.0 release no "local" relocation entries are ever used when * there is a non-zero offset added to a symbol. The "external" and "local" * relocation entries remain unchanged. * * The implemention is quite messy given the compatibility with the existing * relocation entry format. The ASSUMPTION is that a section will never be * bigger than 2**24 - 1 (0x00ffffff or 16,777,215) bytes. This assumption * allows the r_address (which is really an offset) to fit in 24 bits and high * bit of the r_address field in the relocation_info structure to indicate * it is really a scattered_relocation_info structure. Since these are only * used in places where "local" relocation entries are used and not where * "external" relocation entries are used the r_extern field has been removed. * * For scattered loading to work on a RISC machine where some of the references * are split across two instructions the link editor needs to be assured that * each reference has a unique 32 bit reference (that more than one reference is * NOT sharing the same high 16 bits for example) so it move each referenced * item independent of each other. Some compilers guarantees this but the * compilers don't so scattered loading can be done on those that do guarantee * this. */ #if defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__) /* * The reason for the ifdef's of __BIG_ENDIAN__ and __LITTLE_ENDIAN__ are that * when stattered relocation entries were added the mistake of using a mask * against a structure that is made up of bit fields was used. To make this * design work this structure must be laid out in memory the same way so the * mask can be applied can check the same bit each time (r_scattered). */ #endif /* defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__) */ #define R_SCATTERED 0x80000000 /* mask to be applied to the r_address field of a relocation_info structure to tell that is is really a scattered_relocation_info stucture */ struct scattered_relocation_info { #ifdef __BIG_ENDIAN__ uint32_t r_scattered:1, /* 1=scattered, 0=non-scattered (see above) */ r_pcrel:1, /* was relocated pc relative already */ r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */ r_type:4, /* if not 0, machine specific relocation type */ r_address:24; /* offset in the section to what is being relocated */ int32_t r_value; /* the value the item to be relocated is refering to (without any offset added) */ #endif /* __BIG_ENDIAN__ */ #ifdef __LITTLE_ENDIAN__ uint32_t r_address:24, /* offset in the section to what is being relocated */ r_type:4, /* if not 0, machine specific relocation type */ r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */ r_pcrel:1, /* was relocated pc relative already */ r_scattered:1; /* 1=scattered, 0=non-scattered (see above) */ int32_t r_value; /* the value the item to be relocated is refering to (without any offset added) */ #endif /* __LITTLE_ENDIAN__ */ }; /* * Relocation types used in a generic implementation. Relocation entries for * normal things use the generic relocation as discribed above and their r_type * is GENERIC_RELOC_VANILLA (a value of zero). * * Another type of generic relocation, GENERIC_RELOC_SECTDIFF, is to support * the difference of two symbols defined in different sections. That is the * expression "symbol1 - symbol2 + constant" is a relocatable expression when * both symbols are defined in some section. For this type of relocation the * both relocations entries are scattered relocation entries. The value of * symbol1 is stored in the first relocation entry's r_value field and the * value of symbol2 is stored in the pair's r_value field. * * A special case for a prebound lazy pointer is needed to beable to set the * value of the lazy pointer back to its non-prebound state. This is done * using the GENERIC_RELOC_PB_LA_PTR r_type. This is a scattered relocation * entry where the r_value feild is the value of the lazy pointer not prebound. */ enum reloc_type_generic { GENERIC_RELOC_VANILLA, /* generic relocation as discribed above */ GENERIC_RELOC_PAIR, /* Only follows a GENERIC_RELOC_SECTDIFF */ GENERIC_RELOC_SECTDIFF, GENERIC_RELOC_PB_LA_PTR, /* prebound lazy pointer */ GENERIC_RELOC_LOCAL_SECTDIFF }; #endif /* _MACHO_RELOC_H_ */