203 lines
10 KiB
C
203 lines
10 KiB
C
/*
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* Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
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*
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* @APPLE_LICENSE_HEADER_START@
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*
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* This file contains Original Code and/or Modifications of Original Code
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* as defined in and that are subject to the Apple Public Source License
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* Version 2.0 (the 'License'). You may not use this file except in
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* compliance with the License. Please obtain a copy of the License at
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* http://www.opensource.apple.com/apsl/ and read it before using this
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* file.
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*
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* The Original Code and all software distributed under the License are
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* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
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* Please see the License for the specific language governing rights and
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* limitations under the License.
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*
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* @APPLE_LICENSE_HEADER_END@
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*/
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/* $NetBSD: exec.h,v 1.6 1994/10/27 04:16:05 cgd Exp $ */
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/*
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* Copyright (c) 1993 Christopher G. Demetriou
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef _MACHO_RELOC_H_
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#define _MACHO_RELOC_H_
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#include <stdint.h>
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/*
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* Format of a relocation entry of a Mach-O file. Modified from the 4.3BSD
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* format. The modifications from the original format were changing the value
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* of the r_symbolnum field for "local" (r_extern == 0) relocation entries.
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* This modification is required to support symbols in an arbitrary number of
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* sections not just the three sections (text, data and bss) in a 4.3BSD file.
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* Also the last 4 bits have had the r_type tag added to them.
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*/
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struct relocation_info {
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int32_t r_address; /* offset in the section to what is being
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relocated */
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uint32_t r_symbolnum:24, /* symbol index if r_extern == 1 or section
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ordinal if r_extern == 0 */
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r_pcrel:1, /* was relocated pc relative already */
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r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
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r_extern:1, /* does not include value of sym referenced */
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r_type:4; /* if not 0, machine specific relocation type */
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};
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#define R_ABS 0 /* absolute relocation type for Mach-O files */
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/*
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* The r_address is not really the address as it's name indicates but an offset.
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* In 4.3BSD a.out objects this offset is from the start of the "segment" for
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* which relocation entry is for (text or data). For Mach-O object files it is
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* also an offset but from the start of the "section" for which the relocation
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* entry is for. See comments in <mach-o/loader.h> about the r_address feild
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* in images for used with the dynamic linker.
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*
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* In 4.3BSD a.out objects if r_extern is zero then r_symbolnum is an ordinal
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* for the segment the symbol being relocated is in. These ordinals are the
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* symbol types N_TEXT, N_DATA, N_BSS or N_ABS. In Mach-O object files these
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* ordinals refer to the sections in the object file in the order their section
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* structures appear in the headers of the object file they are in. The first
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* section has the ordinal 1, the second 2, and so on. This means that the
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* same ordinal in two different object files could refer to two different
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* sections. And further could have still different ordinals when combined
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* by the link-editor. The value R_ABS is used for relocation entries for
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* absolute symbols which need no further relocation.
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*/
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/*
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* For RISC machines some of the references are split across two instructions
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* and the instruction does not contain the complete value of the reference.
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* In these cases a second, or paired relocation entry, follows each of these
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* relocation entries, using a PAIR r_type, which contains the other part of the
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* reference not contained in the instruction. This other part is stored in the
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* pair's r_address field. The exact number of bits of the other part of the
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* reference store in the r_address field is dependent on the particular
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* relocation type for the particular architecture.
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*/
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/*
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* To make scattered loading by the link editor work correctly "local"
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* relocation entries can't be used when the item to be relocated is the value
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* of a symbol plus an offset (where the resulting expresion is outside the
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* block the link editor is moving, a blocks are divided at symbol addresses).
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* In this case. where the item is a symbol value plus offset, the link editor
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* needs to know more than just the section the symbol was defined. What is
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* needed is the actual value of the symbol without the offset so it can do the
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* relocation correctly based on where the value of the symbol got relocated to
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* not the value of the expression (with the offset added to the symbol value).
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* So for the NeXT 2.0 release no "local" relocation entries are ever used when
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* there is a non-zero offset added to a symbol. The "external" and "local"
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* relocation entries remain unchanged.
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*
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* The implemention is quite messy given the compatibility with the existing
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* relocation entry format. The ASSUMPTION is that a section will never be
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* bigger than 2**24 - 1 (0x00ffffff or 16,777,215) bytes. This assumption
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* allows the r_address (which is really an offset) to fit in 24 bits and high
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* bit of the r_address field in the relocation_info structure to indicate
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* it is really a scattered_relocation_info structure. Since these are only
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* used in places where "local" relocation entries are used and not where
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* "external" relocation entries are used the r_extern field has been removed.
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*
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* For scattered loading to work on a RISC machine where some of the references
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* are split across two instructions the link editor needs to be assured that
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* each reference has a unique 32 bit reference (that more than one reference is
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* NOT sharing the same high 16 bits for example) so it move each referenced
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* item independent of each other. Some compilers guarantees this but the
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* compilers don't so scattered loading can be done on those that do guarantee
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* this.
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*/
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#if defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__)
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/*
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* The reason for the ifdef's of __BIG_ENDIAN__ and __LITTLE_ENDIAN__ are that
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* when stattered relocation entries were added the mistake of using a mask
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* against a structure that is made up of bit fields was used. To make this
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* design work this structure must be laid out in memory the same way so the
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* mask can be applied can check the same bit each time (r_scattered).
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*/
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#endif /* defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__) */
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#define R_SCATTERED 0x80000000 /* mask to be applied to the r_address field
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of a relocation_info structure to tell that
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is is really a scattered_relocation_info
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stucture */
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struct scattered_relocation_info {
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#ifdef __BIG_ENDIAN__
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uint32_t r_scattered:1, /* 1=scattered, 0=non-scattered (see above) */
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r_pcrel:1, /* was relocated pc relative already */
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r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
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r_type:4, /* if not 0, machine specific relocation type */
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r_address:24; /* offset in the section to what is being
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relocated */
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int32_t r_value; /* the value the item to be relocated is
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refering to (without any offset added) */
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#endif /* __BIG_ENDIAN__ */
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#ifdef __LITTLE_ENDIAN__
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uint32_t
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r_address:24, /* offset in the section to what is being
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relocated */
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r_type:4, /* if not 0, machine specific relocation type */
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r_length:2, /* 0=byte, 1=word, 2=long, 3=quad */
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r_pcrel:1, /* was relocated pc relative already */
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r_scattered:1; /* 1=scattered, 0=non-scattered (see above) */
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int32_t r_value; /* the value the item to be relocated is
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refering to (without any offset added) */
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#endif /* __LITTLE_ENDIAN__ */
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};
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/*
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* Relocation types used in a generic implementation. Relocation entries for
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* normal things use the generic relocation as discribed above and their r_type
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* is GENERIC_RELOC_VANILLA (a value of zero).
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*
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* Another type of generic relocation, GENERIC_RELOC_SECTDIFF, is to support
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* the difference of two symbols defined in different sections. That is the
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* expression "symbol1 - symbol2 + constant" is a relocatable expression when
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* both symbols are defined in some section. For this type of relocation the
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* both relocations entries are scattered relocation entries. The value of
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* symbol1 is stored in the first relocation entry's r_value field and the
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* value of symbol2 is stored in the pair's r_value field.
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*
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* A special case for a prebound lazy pointer is needed to beable to set the
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* value of the lazy pointer back to its non-prebound state. This is done
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* using the GENERIC_RELOC_PB_LA_PTR r_type. This is a scattered relocation
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* entry where the r_value feild is the value of the lazy pointer not prebound.
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*/
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enum reloc_type_generic
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{
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GENERIC_RELOC_VANILLA, /* generic relocation as discribed above */
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GENERIC_RELOC_PAIR, /* Only follows a GENERIC_RELOC_SECTDIFF */
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GENERIC_RELOC_SECTDIFF,
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GENERIC_RELOC_PB_LA_PTR, /* prebound lazy pointer */
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GENERIC_RELOC_LOCAL_SECTDIFF
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};
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#endif /* _MACHO_RELOC_H_ */
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