xref: /illumos-gate/usr/src/lib/libdwarf/common/dwarf_macho_loader.h (revision 4d9fdb46)

/*  This is a cut-down version of loader.h from cctools-895,
    shrunk to eliminate aspects unwanted in libdwarf and to avoid
    #include entirely.  All tab characters replaced with 4 spaces
    so various things no line up as they used to.
    cctools-895  in its original form
    is available from https://opensource.apple.com/
    see Developer Tools version 8.2.1. cctools-895/include/loader.h */
/*
* Copyright (c) 1999-2010 Apple 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_LOADER_H
#define MACHO_LOADER_H

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */


#if 0 /* Not used here. DavidA. September 2018 */
/*
* This file describes the format of mach object files.
*/
#include <stdint.h>

/*
* <mach/machine.h> is needed here for the cpu_type_t and cpu_subtype_t types
* and contains the constants for the possible values of these types.
*/
#include <mach/machine.h>

/*
* <mach/vm_prot.h> is needed here for the vm_prot_t type and contains the
* constants that are or'ed together for the possible values of this type.
*/
#include <mach/vm_prot.h>

/*
* <machine/thread_status.h> is expected to define the flavors of the thread
* states and the structures of those flavors for each machine.
*/
#include <mach/machine/thread_status.h>
#include <architecture/byte_order.h>
#endif /* 0 */

#ifndef TYP
#define TYP(n,l) char n[l]
#endif /* TYP */

/*
* The 32-bit mach header appears at the very beginning of the object file for
* 32-bit architectures.
*/
struct mach_header {
    TYP(magic,4); /* mach magic number identifier */
    TYP(cputype,4); /* cpu specifier */
    TYP(cpusubtype,4); /* machine specifier */
    TYP(filetype,4); /* type of file */
    TYP(ncmds,4); /* number of load commands */
    TYP(sizeofcmds,4); /* the size of all the load commands */
    TYP(flags,4); /* flags */
};

/*  Constant for the magic field of the
    mach_header (32-bit architectures)
    MH_MAGIC MH_MAGIC_64 appear in big-endian objects
    MH_CIGAM MH_CIGAM_64 appear in little-endian objects */
#define    MH_MAGIC    0xfeedface    /* the mach magic number */
#define MH_CIGAM    0xcefaedfe    /* NXSwapInt(MH_MAGIC) */

/*
* The 64-bit mach header appears at the very beginning of object files for
* 64-bit architectures.
*/
struct mach_header_64 {
    TYP(magic,4); /* mach magic number identifier */
    TYP(cputype,4); /* cpu specifier */
    TYP(cpusubtype,4); /* machine specifier */
    TYP(filetype,4); /* type of file */
    TYP(ncmds,4); /* number of load commands */
    TYP(sizeofcmds,4); /* the size of all the load commands */
    TYP(flags,4); /* flags */
    TYP(reserved,4); /* reserved */
};

/* Constant for the magic field of the mach_header_64 (64-bit architectures) */
#define MH_MAGIC_64 0xfeedfacf /* the 64-bit mach magic number */
#define MH_CIGAM_64 0xcffaedfe /* NXSwapInt(MH_MAGIC_64) */

/*
* The layout of the file depends on the filetype.  For all but the MH_OBJECT
* file type the segments are padded out and aligned on a segment alignment
* boundary for efficient demand pageing.  The MH_EXECUTE, MH_FVMLIB, MH_DYLIB,
* MH_DYLINKER and MH_BUNDLE file types also have the headers included as part
* of their first segment.
*
* The file type MH_OBJECT is a compact format intended as output of the
* assembler and input (and possibly output) of the link editor (the .o
* format).  All sections are in one unnamed segment with no segment padding.
* This format is used as an executable format when the file is so small the
* segment padding greatly increases its size.
*
* The file type MH_PRELOAD is an executable format intended for things that
* are not executed under the kernel (proms, stand alones, kernels, etc).  The
* format can be executed under the kernel but may demand paged it and not
* preload it before execution.
*
* A core file is in MH_CORE format and can be any in an arbritray legal
* Mach-O file.
*
* Constants for the filetype field of the mach_header
*/
#define    MH_OBJECT    0x1        /* relocatable object file */
#define    MH_EXECUTE    0x2        /* demand paged executable file */
#define    MH_FVMLIB    0x3        /* fixed VM shared library file */
#define    MH_CORE        0x4        /* core file */
#define    MH_PRELOAD    0x5        /* preloaded executable file */
#define    MH_DYLIB    0x6        /* dynamically bound shared library */
#define    MH_DYLINKER    0x7        /* dynamic link editor */
#define    MH_BUNDLE    0x8        /* dynamically bound bundle file */
#define    MH_DYLIB_STUB    0x9        /* shared library stub for static */
    /*  linking only, no section contents */
#define    MH_DSYM        0xa        /* companion file with only debug */
    /*  sections */
#define    MH_KEXT_BUNDLE    0xb        /* x86_64 kexts */

/* Constants for the flags field of the mach_header */
#define    MH_NOUNDEFS    0x1        /* the object file has no undefined
    references */
#define    MH_INCRLINK    0x2        /* the object file is the output of an
    incremental link against a base file
    and can't be link edited again */
#define MH_DYLDLINK    0x4        /* the object file is input for the
    dynamic linker and can't be staticly
    link edited again */
#define MH_BINDATLOAD    0x8        /* the object file's undefined
    references are bound by the dynamic
    linker when loaded. */
#define MH_PREBOUND    0x10        /* the file has its dynamic undefined
    references prebound. */
#define MH_SPLIT_SEGS    0x20        /* the file has its read-only and
    read-write segments split */
#define MH_LAZY_INIT    0x40        /* the shared library init routine is
    to be run lazily via catching memory
    faults to its writeable segments
    (obsolete) */
#define MH_TWOLEVEL    0x80        /* the image is using two-level name
    space bindings */
#define MH_FORCE_FLAT    0x100        /* the executable is forcing all images
    to use flat name space bindings */
#define MH_NOMULTIDEFS    0x200        /* this umbrella guarantees no multiple
    defintions of symbols in its
    sub-images so the two-level namespace
    hints can always be used. */
#define MH_NOFIXPREBINDING 0x400    /* do not have dyld notify the
    prebinding agent about this
    executable */
#define MH_PREBINDABLE  0x800           /* the binary is not prebound but can
    have its prebinding redone. only used
    when MH_PREBOUND is not set. */
#define MH_ALLMODSBOUND 0x1000        /* indicates that this binary binds to
    all two-level namespace modules of
    its dependent libraries. only used
    when MH_PREBINDABLE and MH_TWOLEVEL
    are both set. */
#define MH_SUBSECTIONS_VIA_SYMBOLS 0x2000/* safe to divide up the sections into
    sub-sections via symbols for dead
    code stripping */
#define MH_CANONICAL    0x4000        /* the binary has been canonicalized
    via the unprebind operation */
#define MH_WEAK_DEFINES    0x8000        /* the final linked image contains
    external weak symbols */
#define MH_BINDS_TO_WEAK 0x10000    /* the final linked image uses
    weak symbols */

#define MH_ALLOW_STACK_EXECUTION 0x20000/* When this bit is set, all stacks
    in the task will be given stack
    execution privilege.  Only used in
    MH_EXECUTE filetypes. */
#define MH_ROOT_SAFE 0x40000           /* When this bit is set, the binary
    declares it is safe for use in
    processes with uid zero */

#define MH_SETUID_SAFE 0x80000         /* When this bit is set, the binary
    declares it is safe for use in
    processes when issetugid() is true */

#define MH_NO_REEXPORTED_DYLIBS 0x100000 /* When this bit is set on a dylib,
    the static linker does not need to
    examine dependent dylibs to see
    if any are re-exported */
#define    MH_PIE 0x200000            /* When this bit is set, the OS will
    load the main executable at a
    random address.  Only used in
    MH_EXECUTE filetypes. */
#define    MH_DEAD_STRIPPABLE_DYLIB 0x400000 /* Only for use on dylibs.  When
    linking against a dylib that
    has this bit set, the static linker
    will automatically not create a
    LC_LOAD_DYLIB load command to the
    dylib if no symbols are being
    referenced from the dylib. */
#define MH_HAS_TLV_DESCRIPTORS 0x800000 /* Contains a section of type
    S_THREAD_LOCAL_VARIABLES */

#define MH_NO_HEAP_EXECUTION 0x1000000    /* When this bit is set, the OS will
    run the main executable with
    a non-executable heap even on
    platforms (e.g. i386) that don't
    require it. Only used in MH_EXECUTE
    filetypes. */

#define MH_APP_EXTENSION_SAFE 0x02000000 /* The code was linked for use in an
    application extension. */

/*
* The load commands directly follow the mach_header.  The total size of all
* of the commands is given by the sizeofcmds field in the mach_header.  All
* load commands must have as their first two fields cmd and cmdsize.  The cmd
* field is filled in with a constant for that command type.  Each command type
* has a structure specifically for it.  The cmdsize field is the size in bytes
* of the particular load command structure plus anything that follows it that
* is a part of the load command (i.e. section structures, strings, etc.).  To
* advance to the next load command the cmdsize can be added to the offset or
* pointer of the current load command.  The cmdsize for 32-bit architectures
* MUST be a multiple of 4 bytes and for 64-bit architectures MUST be a multiple
* of 8 bytes (these are forever the maximum alignment of any load commands).
* The padded bytes must be zero.  All tables in the object file must also
* follow these rules so the file can be memory mapped.  Otherwise the pointers
* to these tables will not work well or at all on some machines.  With all
* padding zeroed like objects will compare byte for byte.
*/
struct load_command {
    TYP(cmd,4); /* type of load command */
    TYP(cmdsize,4); /* total size of command in bytes */
};

/*
* After MacOS X 10.1 when a new load command is added that is required to be
* understood by the dynamic linker for the image to execute properly the
* LC_REQ_DYLD bit will be or'ed into the load command constant.  If the dynamic
* linker sees such a load command it it does not understand will issue a
* "unknown load command required for execution" error and refuse to use the
* image.  Other load commands without this bit that are not understood will
* simply be ignored.
*/
#define LC_REQ_DYLD 0x80000000

/* Constants for the cmd field of all load commands, the type */
#define    LC_SEGMENT    0x1    /* segment of this file to be mapped */
#define    LC_SYMTAB    0x2    /* link-edit stab symbol table info */
#define    LC_SYMSEG    0x3    /* link-edit gdb symbol table info (obsolete) */
#define    LC_THREAD    0x4    /* thread */
#define    LC_UNIXTHREAD    0x5    /* unix thread (includes a stack) */
#define    LC_LOADFVMLIB    0x6    /* load a specified fixed VM shared library */
#define    LC_IDFVMLIB    0x7    /* fixed VM shared library identification */
#define    LC_IDENT    0x8    /* object identification info (obsolete) */
#define LC_FVMFILE    0x9    /* fixed VM file inclusion (internal use) */
#define LC_PREPAGE      0xa     /* prepage command (internal use) */
#define    LC_DYSYMTAB    0xb    /* dynamic link-edit symbol table info */
#define    LC_LOAD_DYLIB    0xc    /* load a dynamically linked shared library */
#define    LC_ID_DYLIB    0xd    /* dynamically linked shared lib ident */
#define LC_LOAD_DYLINKER 0xe    /* load a dynamic linker */
#define LC_ID_DYLINKER    0xf    /* dynamic linker identification */
#define    LC_PREBOUND_DYLIB 0x10    /* modules prebound for a dynamically */
    /*  linked shared library */
#define    LC_ROUTINES    0x11    /* image routines */
#define    LC_SUB_FRAMEWORK 0x12    /* sub framework */
#define    LC_SUB_UMBRELLA 0x13    /* sub umbrella */
#define    LC_SUB_CLIENT    0x14    /* sub client */
#define    LC_SUB_LIBRARY  0x15    /* sub library */
#define    LC_TWOLEVEL_HINTS 0x16    /* two-level namespace lookup hints */
#define    LC_PREBIND_CKSUM  0x17    /* prebind checksum */

/*
* load a dynamically linked shared library that is allowed to be missing
* (all symbols are weak imported).
*/
#define    LC_LOAD_WEAK_DYLIB (0x18 | LC_REQ_DYLD)

#define    LC_SEGMENT_64    0x19    /* 64-bit segment of this file to be
    mapped */
#define    LC_ROUTINES_64    0x1a    /* 64-bit image routines */
#define LC_UUID        0x1b    /* the uuid */
#define LC_RPATH       (0x1c | LC_REQ_DYLD)    /* runpath additions */
#define LC_CODE_SIGNATURE 0x1d    /* local of code signature */
#define LC_SEGMENT_SPLIT_INFO 0x1e /* local of info to split segments */
#define LC_REEXPORT_DYLIB (0x1f | LC_REQ_DYLD) /* load and re-export dylib */
#define    LC_LAZY_LOAD_DYLIB 0x20    /* delay load of dylib until first use */
#define    LC_ENCRYPTION_INFO 0x21    /* encrypted segment information */
#define    LC_DYLD_INFO     0x22    /* compressed dyld information */
#define    LC_DYLD_INFO_ONLY (0x22|LC_REQ_DYLD)    /* compressed dyld information only */
#define    LC_LOAD_UPWARD_DYLIB (0x23 | LC_REQ_DYLD) /* load upward dylib */
#define LC_VERSION_MIN_MACOSX 0x24   /* build for MacOSX min OS version */
#define LC_VERSION_MIN_IPHONEOS 0x25 /* build for iPhoneOS min OS version */
#define LC_FUNCTION_STARTS 0x26 /* compressed table of function start addresses */
#define LC_DYLD_ENVIRONMENT 0x27 /* string for dyld to treat
                    like environment variable */
#define LC_MAIN (0x28|LC_REQ_DYLD) /* replacement for LC_UNIXTHREAD */
#define LC_DATA_IN_CODE 0x29 /* table of non-instructions in __text */
#define LC_SOURCE_VERSION 0x2A /* source version used to build binary */
#define LC_DYLIB_CODE_SIGN_DRS 0x2B /* Code signing DRs copied from linked dylibs */
#define    LC_ENCRYPTION_INFO_64 0x2C /* 64-bit encrypted segment information */
#define LC_LINKER_OPTION 0x2D /* linker options in MH_OBJECT files */
#define LC_LINKER_OPTIMIZATION_HINT 0x2E /* optimization hints in MH_OBJECT files */
#define LC_VERSION_MIN_TVOS 0x2F /* build for AppleTV min OS version */
#define LC_VERSION_MIN_WATCHOS 0x30 /* build for Watch min OS version */

/*
* A variable length string in a load command is represented by an lc_str
* union.  The strings are stored just after the load command structure and
* the offset is from the start of the load command structure.  The size
* of the string is reflected in the cmdsize field of the load command.
* Once again any padded bytes to bring the cmdsize field to a multiple
* of 4 bytes must be zero.
*/
union lc_str {
    TYP(offset,4); /* offset to the string */
#ifndef __LP64__
    char        *ptr;    /* pointer to the string */
#endif
};

/*
* The segment load command indicates that a part of this file is to be
* mapped into the task's address space.  The size of this segment in memory,
* vmsize, maybe equal to or larger than the amount to map from this file,
* filesize.  The file is mapped starting at fileoff to the beginning of
* the segment in memory, vmaddr.  The rest of the memory of the segment,
* if any, is allocated zero fill on demand.  The segment's maximum virtual
* memory protection and initial virtual memory protection are specified
* by the maxprot and initprot fields.  If the segment has sections then the
* section structures directly follow the segment command and their size is
* reflected in cmdsize.
*/
struct segment_command { /* for 32-bit architectures */
    TYP(cmd,4); /* LC_SEGMENT */
    TYP(cmdsize,4); /* includes sizeof section structs */
    char        segname[16];    /* segment name */
    TYP(vmaddr,4); /* memory address of this segment */
    TYP(vmsize,4); /* memory size of this segment */
    TYP(fileoff,4); /* file offset of this segment */
    TYP(filesize,4); /* amount to map from the file */
    TYP(maxprot,4); /* maximum VM protection */
    TYP(initprot,4); /* initial VM protection */
    TYP(nsects,4); /* number of sections in segment */
    TYP(flags,4); /* flags */
};

/*
* The 64-bit segment load command indicates that a part of this file is to be
* mapped into a 64-bit task's address space.  If the 64-bit segment has
* sections then section_64 structures directly follow the 64-bit segment
* command and their size is reflected in cmdsize.
*/
struct segment_command_64 { /* for 64-bit architectures */
    TYP(cmd,4); /* LC_SEGMENT_64 */
    TYP(cmdsize,4); /* includes sizeof section_64 structs */
    char        segname[16];    /* segment name */
    TYP(vmaddr,8); /* memory address of this segment */
    TYP(vmsize,8); /* memory size of this segment */
    TYP(fileoff,8); /* file offset of this segment */
    TYP(filesize,8); /* amount to map from the file */
    TYP(maxprot,4); /* maximum VM protection */
    TYP(initprot,4); /* initial VM protection */
    TYP(nsects,4); /* number of sections in segment */
    TYP(flags,4); /* flags */
};

/* Constants for the flags field of the segment_command */
#define    SG_HIGHVM    0x1    /* the file contents for this segment is for
    the high part of the VM space, the low part
    is zero filled (for stacks in core files) */
#define    SG_FVMLIB    0x2    /* this segment is the VM that is allocated by
    a fixed VM library, for overlap checking in
    the link editor */
#define    SG_NORELOC    0x4    /* this segment has nothing that was relocated
    in it and nothing relocated to it, that is
    it maybe safely replaced without relocation*/
#define SG_PROTECTED_VERSION_1    0x8 /* This segment is protected.  If the
    segment starts at file offset 0, the
    first page of the segment is not
    protected.  All other pages of the
    segment are protected. */

/*
* A segment is made up of zero or more sections.  Non-MH_OBJECT files have
* all of their segments with the proper sections in each, and padded to the
* specified segment alignment when produced by the link editor.  The first
* segment of a MH_EXECUTE and MH_FVMLIB format file contains the mach_header
* and load commands of the object file before its first section.  The zero
* fill sections are always last in their segment (in all formats).  This
* allows the zeroed segment padding to be mapped into memory where zero fill
* sections might be. The gigabyte zero fill sections, those with the section
* type S_GB_ZEROFILL, can only be in a segment with sections of this type.
* These segments are then placed after all other segments.
*
* The MH_OBJECT format has all of its sections in one segment for
* compactness.  There is no padding to a specified segment boundary and the
* mach_header and load commands are not part of the segment.
*
* Sections with the same section name, sectname, going into the same segment,
* segname, are combined by the link editor.  The resulting section is aligned
* to the maximum alignment of the combined sections and is the new section's
* alignment.  The combined sections are aligned to their original alignment in
* the combined section.  Any padded bytes to get the specified alignment are
* zeroed.
*
* The format of the relocation entries referenced by the reloff and nreloc
* fields of the section structure for mach object files is described in the
* header file <reloc.h>.
*/
struct section { /* for 32-bit architectures */
    char        sectname[16];    /* name of this section */
    char        segname[16];    /* segment this section goes in */
    TYP(addr,4); /* memory address of this section */
    TYP(size,4); /* size in bytes of this section */
    TYP(offset,4); /* file offset of this section */
    TYP(align,4); /* section alignment (power of 2) */
    TYP(reloff,4); /* file offset of relocation entries */
    TYP(nreloc,4); /* number of relocation entries */
    TYP(flags,4); /* flags (section type and attributes)*/
    TYP(reserved1,4); /* reserved (for offset or index) */
    TYP(reserved2,4); /* reserved (for count or sizeof) */
};

struct section_64 { /* for 64-bit architectures */
    char        sectname[16];    /* name of this section */
    char        segname[16];    /* segment this section goes in */
    TYP(addr,8); /* memory address of this section */
    TYP(size,8); /* size in bytes of this section */
    TYP(offset,4); /* file offset of this section */
    TYP(align,4); /* section alignment (power of 2) */
    TYP(reloff,4); /* file offset of relocation entries */
    TYP(nreloc,4); /* number of relocation entries */
    TYP(flags,4); /* flags (section type and attributes)*/
    TYP(reserved1,4); /* reserved (for offset or index) */
    TYP(reserved2,4); /* reserved (for count or sizeof) */
    TYP(reserved3,4); /* reserved */
};

/*
* The flags field of a section structure is separated into two parts a section
* type and section attributes.  The section types are mutually exclusive (it
* can only have one type) but the section attributes are not (it may have more
* than one attribute).
*/
#define SECTION_TYPE         0x000000ff    /* 256 section types */
#define SECTION_ATTRIBUTES     0xffffff00    /*  24 section attributes */

/* Constants for the type of a section */
#define    S_REGULAR        0x0    /* regular section */
#define    S_ZEROFILL        0x1    /* zero fill on demand section */
#define    S_CSTRING_LITERALS    0x2    /* section with only literal C strings*/
#define    S_4BYTE_LITERALS    0x3    /* section with only 4 byte literals */
#define    S_8BYTE_LITERALS    0x4    /* section with only 8 byte literals */
#define    S_LITERAL_POINTERS    0x5    /* section with only pointers to */
    /*  literals */
/*
* For the two types of symbol pointers sections and the symbol stubs section
* they have indirect symbol table entries.  For each of the entries in the
* section the indirect symbol table entries, in corresponding order in the
* indirect symbol table, start at the index stored in the reserved1 field
* of the section structure.  Since the indirect symbol table entries
* correspond to the entries in the section the number of indirect symbol table
* entries is inferred from the size of the section divided by the size of the
* entries in the section.  For symbol pointers sections the size of the entries
* in the section is 4 bytes and for symbol stubs sections the byte size of the
* stubs is stored in the reserved2 field of the section structure.
*/
#define    S_NON_LAZY_SYMBOL_POINTERS    0x6    /* section with only non-lazy
    symbol pointers */
#define    S_LAZY_SYMBOL_POINTERS        0x7    /* section with only lazy symbol
    pointers */
#define    S_SYMBOL_STUBS            0x8    /* section with only symbol
    stubs, byte size of stub in
    the reserved2 field */
#define    S_MOD_INIT_FUNC_POINTERS    0x9    /* section with only function
    pointers for initialization*/
#define    S_MOD_TERM_FUNC_POINTERS    0xa    /* section with only function
    pointers for termination */
#define    S_COALESCED            0xb    /* section contains symbols that
    are to be coalesced */
#define    S_GB_ZEROFILL            0xc    /* zero fill on demand section
    (that can be larger than 4
    gigabytes) */
#define    S_INTERPOSING            0xd    /* section with only pairs of
    function pointers for
    interposing */
#define    S_16BYTE_LITERALS        0xe    /* section with only 16 byte
    literals */
#define    S_DTRACE_DOF            0xf    /* section contains
    DTrace Object Format */
#define    S_LAZY_DYLIB_SYMBOL_POINTERS    0x10    /* section with only lazy
    symbol pointers to lazy
    loaded dylibs */
/*
* Section types to support thread local variables
*/
#define S_THREAD_LOCAL_REGULAR                   0x11  /* template of initial
    values for TLVs */
#define S_THREAD_LOCAL_ZEROFILL                  0x12  /* template of initial
    values for TLVs */
#define S_THREAD_LOCAL_VARIABLES                 0x13  /* TLV descriptors */
#define S_THREAD_LOCAL_VARIABLE_POINTERS         0x14  /* pointers to TLV
    descriptors */
#define S_THREAD_LOCAL_INIT_FUNCTION_POINTERS    0x15  /* functions to call
    to initialize TLV
    values */

/*
* Constants for the section attributes part of the flags field of a section
* structure.
*/
#define SECTION_ATTRIBUTES_USR     0xff000000    /* User setable attributes */
#define S_ATTR_PURE_INSTRUCTIONS 0x80000000    /* section contains only true
    machine instructions */
#define S_ATTR_NO_TOC          0x40000000    /* section contains coalesced
    symbols that are not to be
    in a ranlib table of
    contents */
#define S_ATTR_STRIP_STATIC_SYMS 0x20000000    /* ok to strip static symbols
    in this section in files
    with the MH_DYLDLINK flag */
#define S_ATTR_NO_DEAD_STRIP     0x10000000    /* no dead stripping */
#define S_ATTR_LIVE_SUPPORT     0x08000000    /* blocks are live if they
    reference live blocks */
#define S_ATTR_SELF_MODIFYING_CODE 0x04000000    /* Used with i386 code stubs
    written on by dyld */
/*
* If a segment contains any sections marked with S_ATTR_DEBUG then all
* sections in that segment must have this attribute.  No section other than
* a section marked with this attribute may reference the contents of this
* section.  A section with this attribute may contain no symbols and must have
* a section type S_REGULAR.  The static linker will not copy section contents
* from sections with this attribute into its output file.  These sections
* generally contain DWARF debugging info.
*/
#define    S_ATTR_DEBUG         0x02000000    /* a debug section */
#define SECTION_ATTRIBUTES_SYS     0x00ffff00    /* system setable attributes */
#define S_ATTR_SOME_INSTRUCTIONS 0x00000400    /* section contains some
    machine instructions */
#define S_ATTR_EXT_RELOC     0x00000200    /* section has external
    relocation entries */
#define S_ATTR_LOC_RELOC     0x00000100    /* section has local
    relocation entries */


/*
* The names of segments and sections in them are mostly meaningless to the
* link-editor.  But there are few things to support traditional UNIX
* executables that require the link-editor and assembler to use some names
* agreed upon by convention.
*
* The initial protection of the "__TEXT" segment has write protection turned
* off (not writeable).
*
* The link-editor will allocate common symbols at the end of the "__common"
* section in the "__DATA" segment.  It will create the section and segment
* if needed.
*/

/* The currently known segment names and the section names in those segments */

#define    SEG_PAGEZERO    "__PAGEZERO"    /* the pagezero segment which has no */
                    /* protections and catches NULL */
                    /* references for MH_EXECUTE files */


#define    SEG_TEXT    "__TEXT"    /* the tradition UNIX text segment */
#define    SECT_TEXT    "__text"    /* the real text part of the text */
                    /* section no headers, and no padding */
#define SECT_FVMLIB_INIT0 "__fvmlib_init0"    /* the fvmlib initialization */
                        /*  section */
#define SECT_FVMLIB_INIT1 "__fvmlib_init1"    /* the section following the */
                            /*  fvmlib initialization */
                        /*  section */

#define    SEG_DATA    "__DATA"    /* the tradition UNIX data segment */
#define    SECT_DATA    "__data"    /* the real initialized data section */
                    /* no padding, no bss overlap */
#define    SECT_BSS    "__bss"        /* the real uninitialized data section*/
                    /* no padding */
#define SECT_COMMON    "__common"    /* the section common symbols are */
                    /* allocated in by the link editor */

#define    SEG_OBJC    "__OBJC"    /* objective-C runtime segment */
#define SECT_OBJC_SYMBOLS "__symbol_table"    /* symbol table */
#define SECT_OBJC_MODULES "__module_info"    /* module information */
#define SECT_OBJC_STRINGS "__selector_strs"    /* string table */
#define SECT_OBJC_REFS "__selector_refs"    /* string table */

#define    SEG_ICON     "__ICON"    /* the icon segment */
#define    SECT_ICON_HEADER "__header"    /* the icon headers */
#define    SECT_ICON_TIFF   "__tiff"    /* the icons in tiff format */

#define    SEG_LINKEDIT    "__LINKEDIT"    /* the segment containing all structs */
                    /* created and maintained by the link */
                    /* editor.  Created with -seglinkedit */
                    /* option to ld(1) for MH_EXECUTE and */
                    /* FVMLIB file types only */

#define SEG_UNIXSTACK    "__UNIXSTACK"    /* the unix stack segment */

#define SEG_IMPORT    "__IMPORT"    /* the segment for the self (dyld) */
                    /* modifing code stubs that has read, */
                    /* write and execute permissions */

/*
* Fixed virtual memory shared libraries are identified by two things.  The
* target pathname (the name of the library as found for execution), and the
* minor version number.  The address of where the headers are loaded is in
* header_addr. (THIS IS OBSOLETE and no longer supported).
*/
struct fvmlib {
    union lc_str    name;        /* library's target pathname */
    TYP(minor_version,4); /* library's minor version number */
    TYP(header_addr,4); /* library's header address */
};

/*
* A fixed virtual shared library (filetype == MH_FVMLIB in the mach header)
* contains a fvmlib_command (cmd == LC_IDFVMLIB) to identify the library.
* An object that uses a fixed virtual shared library also contains a
* fvmlib_command (cmd == LC_LOADFVMLIB) for each library it uses.
* (THIS IS OBSOLETE and no longer supported).
*/
struct fvmlib_command {
    TYP(cmd,4); /* LC_IDFVMLIB or LC_LOADFVMLIB */
    TYP(cmdsize,4); /* includes pathname string */
    struct fvmlib    fvmlib;        /* the library identification */
};

/*
* Dynamicly linked shared libraries are identified by two things.  The
* pathname (the name of the library as found for execution), and the
* compatibility version number.  The pathname must match and the compatibility
* number in the user of the library must be greater than or equal to the
* library being used.  The time stamp is used to record the time a library was
* built and copied into user so it can be use to determined if the library used
* at runtime is exactly the same as used to built the program.
*/
struct dylib {
    union lc_str  name;            /* library's path name */
    TYP(timestamp,4); /* library's build time stamp */
    TYP(current_version,4); /* library's current version number */
    TYP(compatibility_version,4); /* library's compatibility vers number*/
};

/*
* A dynamically linked shared library (filetype == MH_DYLIB in the mach header)
* contains a dylib_command (cmd == LC_ID_DYLIB) to identify the library.
* An object that uses a dynamically linked shared library also contains a
* dylib_command (cmd == LC_LOAD_DYLIB, LC_LOAD_WEAK_DYLIB, or
* LC_REEXPORT_DYLIB) for each library it uses.
*/
struct dylib_command {
    TYP(cmd,4); /* LC_ID_DYLIB, LC_LOAD_{,WEAK_}DYLIB,
        LC_REEXPORT_DYLIB */
    TYP(cmdsize,4); /* includes pathname string */
    struct dylib    dylib;        /* the library identification */
};

/*
* A dynamically linked shared library may be a subframework of an umbrella
* framework.  If so it will be linked with "-umbrella umbrella_name" where
* Where "umbrella_name" is the name of the umbrella framework. A subframework
* can only be linked against by its umbrella framework or other subframeworks
* that are part of the same umbrella framework.  Otherwise the static link
* editor produces an error and states to link against the umbrella framework.
* The name of the umbrella framework for subframeworks is recorded in the
* following structure.
*/
struct sub_framework_command {
    TYP(cmd,4); /* LC_SUB_FRAMEWORK */
    TYP(cmdsize,4); /* includes umbrella string */
    union lc_str     umbrella;    /* the umbrella framework name */
};

/*
* For dynamically linked shared libraries that are subframework of an umbrella
* framework they can allow clients other than the umbrella framework or other
* subframeworks in the same umbrella framework.  To do this the subframework
* is built with "-allowable_client client_name" and an LC_SUB_CLIENT load
* command is created for each -allowable_client flag.  The client_name is
* usually a framework name.  It can also be a name used for bundles clients
* where the bundle is built with "-client_name client_name".
*/
struct sub_client_command {
    TYP(cmd,4); /* LC_SUB_CLIENT */
    TYP(cmdsize,4); /* includes client string */
    union lc_str     client;        /* the client name */
};

/*
* A dynamically linked shared library may be a sub_umbrella of an umbrella
* framework.  If so it will be linked with "-sub_umbrella umbrella_name" where
* Where "umbrella_name" is the name of the sub_umbrella framework.  When
* staticly linking when -twolevel_namespace is in effect a twolevel namespace
* umbrella framework will only cause its subframeworks and those frameworks
* listed as sub_umbrella frameworks to be implicited linked in.  Any other
* dependent dynamic libraries will not be linked it when -twolevel_namespace
* is in effect.  The primary library recorded by the static linker when
* resolving a symbol in these libraries will be the umbrella framework.
* Zero or more sub_umbrella frameworks may be use by an umbrella framework.
* The name of a sub_umbrella framework is recorded in the following structure.
*/
struct sub_umbrella_command {
    TYP(cmd,4); /* LC_SUB_UMBRELLA */
    TYP(cmdsize,4); /* includes sub_umbrella string */
    union lc_str     sub_umbrella;    /* the sub_umbrella framework name */
};

/*
* A dynamically linked shared library may be a sub_library of another shared
* library.  If so it will be linked with "-sub_library library_name" where
* Where "library_name" is the name of the sub_library shared library.  When
* staticly linking when -twolevel_namespace is in effect a twolevel namespace
* shared library will only cause its subframeworks and those frameworks
* listed as sub_umbrella frameworks and libraries listed as sub_libraries to
* be implicited linked in.  Any other dependent dynamic libraries will not be
* linked it when -twolevel_namespace is in effect.  The primary library
* recorded by the static linker when resolving a symbol in these libraries
* will be the umbrella framework (or dynamic library). Zero or more sub_library
* shared libraries may be use by an umbrella framework or (or dynamic library).
* The name of a sub_library framework is recorded in the following structure.
* For example /usr/lib/libobjc_profile.A.dylib would be recorded as "libobjc".
*/
struct sub_library_command {
    TYP(cmd,4); /* LC_SUB_LIBRARY */
    TYP(cmdsize,4); /* includes sub_library string */
    union lc_str     sub_library;    /* the sub_library name */
};

/*
* A program (filetype == MH_EXECUTE) that is
* prebound to its dynamic libraries has one of these for each library that
* the static linker used in prebinding.  It contains a bit vector for the
* modules in the library.  The bits indicate which modules are bound (1) and
* which are not (0) from the library.  The bit for module 0 is the low bit
* of the first byte.  So the bit for the Nth module is:
* (linked_modules[N/8] >> N%8) & 1
*/
struct prebound_dylib_command {
    TYP(cmd,4); /* LC_PREBOUND_DYLIB */
    TYP(cmdsize,4); /* includes strings */
    union lc_str    name;        /* library's path name */
    TYP(nmodules,4); /* number of modules in library */
    union lc_str    linked_modules;    /* bit vector of linked modules */
};

/*
* A program that uses a dynamic linker contains a dylinker_command to identify
* the name of the dynamic linker (LC_LOAD_DYLINKER).  And a dynamic linker
* contains a dylinker_command to identify the dynamic linker (LC_ID_DYLINKER).
* A file can have at most one of these.
* This struct is also used for the LC_DYLD_ENVIRONMENT load command and
* contains string for dyld to treat like environment variable.
*/
struct dylinker_command {
    TYP(cmd,4); /* LC_ID_DYLINKER, LC_LOAD_DYLINKER or
        LC_DYLD_ENVIRONMENT */
    TYP(cmdsize,4); /* includes pathname string */
    union lc_str    name;        /* dynamic linker's path name */
};

/*
* Thread commands contain machine-specific data structures suitable for
* use in the thread state primitives.  The machine specific data structures
* follow the struct thread_command as follows.
* Each flavor of machine specific data structure is preceded by an unsigned
* long constant for the flavor of that data structure, an uint32_t
* that is the count of longs of the size of the state data structure and then
* the state data structure follows.  This triple may be repeated for many
* flavors.  The constants for the flavors, counts and state data structure
* definitions are expected to be in the header file <machine/thread_status.h>.
* These machine specific data structures sizes must be multiples of
* 4 bytes  The cmdsize reflects the total size of the thread_command
* and all of the sizes of the constants for the flavors, counts and state
* data structures.
*
* For executable objects that are unix processes there will be one
* thread_command (cmd == LC_UNIXTHREAD) created for it by the link-editor.
* This is the same as a LC_THREAD, except that a stack is automatically
* created (based on the shell's limit for the stack size).  Command arguments
* and environment variables are copied onto that stack.
*/
struct thread_command {
    TYP(cmd,4); /* LC_THREAD or LC_UNIXTHREAD */
    TYP(cmdsize,4); /* total size of this command */
    /* uint32_t flavor           flavor of thread state */
    /* uint32_t count           count of longs in thread state */
    /* struct XXX_thread_state state   thread state for this flavor */
    /* ... */
};

/*
* The routines command contains the address of the dynamic shared library
* initialization routine and an index into the module table for the module
* that defines the routine.  Before any modules are used from the library the
* dynamic linker fully binds the module that defines the initialization routine
* and then calls it.  This gets called before any module initialization
* routines (used for C++ static constructors) in the library.
*/
struct routines_command { /* for 32-bit architectures */
    TYP(cmd,4); /* LC_ROUTINES */
    TYP(cmdsize,4); /* total size of this command */
    TYP(init_address,4); /* address of initialization routine */
    TYP(init_module,4); /* index into the module table that */
        /*  the init routine is defined in */
    TYP(reserved1,4);
    TYP(reserved2,4);
    TYP(reserved3,4);
    TYP(reserved4,4);
    TYP(reserved5,4);
    TYP(reserved6,4);
};

/*
* The 64-bit routines command.  Same use as above.
*/
struct routines_command_64 { /* for 64-bit architectures */
    TYP(cmd,4); /* LC_ROUTINES_64 */
    TYP(cmdsize,4); /* total size of this command */
    TYP(init_address,8); /* address of initialization routine */
    TYP(init_module,8); /* index into the module table that */
        /*  the init routine is defined in */
    TYP(reserved1,8);
    TYP(reserved2,8);
    TYP(reserved3,8);
    TYP(reserved4,8);
    TYP(reserved5,8);
    TYP(reserved6,8);
};

/*
* The symtab_command contains the offsets and sizes of the link-edit 4.3BSD
* "stab" style symbol table information as described in the header files
* <nlist.h> and <stab.h>.
*/
struct symtab_command {
    TYP(cmd,4); /* LC_SYMTAB */
    TYP(cmdsize,4); /* sizeof(struct symtab_command) */
    TYP(symoff,4); /* symbol table offset */
    TYP(nsyms,4); /* number of symbol table entries */
    TYP(stroff,4); /* string table offset */
    TYP(strsize,4); /* string table size in bytes */
};

/*
* This is the second set of the symbolic information which is used to support
* the data structures for the dynamically link editor.
*
* The original set of symbolic information in the symtab_command which contains
* the symbol and string tables must also be present when this load command is
* present.  When this load command is present the symbol table is organized
* into three groups of symbols:
*    local symbols (static and debugging symbols) - grouped by module
*    defined external symbols - grouped by module (sorted by name if not lib)
*    undefined external symbols (sorted by name if MH_BINDATLOAD is not set,
*                         and in order the were seen by the static
*                    linker if MH_BINDATLOAD is set)
* In this load command there are offsets and counts to each of the three groups
* of symbols.
*
* This load command contains a the offsets and sizes of the following new
* symbolic information tables:
*    table of contents
*    module table
*    reference symbol table
*    indirect symbol table
* The first three tables above (the table of contents, module table and
* reference symbol table) are only present if the file is a dynamically linked
* shared library.  For executable and object modules, which are files
* containing only one module, the information that would be in these three
* tables is determined as follows:
*     table of contents - the defined external symbols are sorted by name
*    module table - the file contains only one module so everything in the
*               file is part of the module.
*    reference symbol table - is the defined and undefined external symbols
*
* For dynamically linked shared library files this load command also contains
* offsets and sizes to the pool of relocation entries for all sections
* separated into two groups:
*    external relocation entries
*    local relocation entries
* For executable and object modules the relocation entries continue to hang
* off the section structures.
*/
struct dysymtab_command {
    TYP(cmd,4); /* LC_DYSYMTAB */
    TYP(cmdsize,4); /* sizeof(struct dysymtab_command) */

    /*
    * The symbols indicated by symoff and nsyms of the LC_SYMTAB load command
    * are grouped into the following three groups:
    *    local symbols (further grouped by the module they are from)
    *    defined external symbols (further grouped by the module they are from)
    *    undefined symbols
    *
    * The local symbols are used only for debugging.  The dynamic binding
    * process may have to use them to indicate to the debugger the local
    * symbols for a module that is being bound.
    *
    * The last two groups are used by the dynamic binding process to do the
    * binding (indirectly through the module table and the reference symbol
    * table when this is a dynamically linked shared library file).
    */
    TYP(ilocalsym,4); /* index to local symbols */
    TYP(nlocalsym,4); /* number of local symbols */

    TYP(iextdefsym,4); /* index to externally defined symbols */
    TYP(nextdefsym,4); /* number of externally defined symbols */

    TYP(iundefsym,4); /* index to undefined symbols */
    TYP(nundefsym,4); /* number of undefined symbols */

    /*
    * For the for the dynamic binding process to find which module a symbol
    * is defined in the table of contents is used (analogous to the ranlib
    * structure in an archive) which maps defined external symbols to modules
    * they are defined in.  This exists only in a dynamically linked shared
    * library file.  For executable and object modules the defined external
    * symbols are sorted by name and is use as the table of contents.
    */
    TYP(tocoff,4); /* file offset to table of contents */
    TYP(ntoc,4); /* number of entries in table of contents */

    /*
    * To support dynamic binding of "modules" (whole object files) the symbol
    * table must reflect the modules that the file was created from.  This is
    * done by having a module table that has indexes and counts into the merged
    * tables for each module.  The module structure that these two entries
    * refer to is described below.  This exists only in a dynamically linked
    * shared library file.  For executable and object modules the file only
    * contains one module so everything in the file belongs to the module.
    */
    TYP(modtaboff,4); /* file offset to module table */
    TYP(nmodtab,4); /* number of module table entries */

    /*
    * To support dynamic module binding the module structure for each module
    * indicates the external references (defined and undefined) each module
    * makes.  For each module there is an offset and a count into the
    * reference symbol table for the symbols that the module references.
    * This exists only in a dynamically linked shared library file.  For
    * executable and object modules the defined external symbols and the
    * undefined external symbols indicates the external references.
    */
    TYP(extrefsymoff,4); /* offset to referenced symbol table */
    TYP(nextrefsyms,4); /* number of referenced symbol table entries */

    /*
    * The sections that contain "symbol pointers" and "routine stubs" have
    * indexes and (implied counts based on the size of the section and fixed
    * size of the entry) into the "indirect symbol" table for each pointer
    * and stub.  For every section of these two types the index into the
    * indirect symbol table is stored in the section header in the field
    * reserved1.  An indirect symbol table entry is simply a 32bit index into
    * the symbol table to the symbol that the pointer or stub is referring to.
    * The indirect symbol table is ordered to match the entries in the section.
    */
    TYP(indirectsymoff,4); /* file offset to the indirect symbol table */
    TYP(nindirectsyms,4); /* number of indirect symbol table entries */

    /*
    * To support relocating an individual module in a library file quickly the
    * external relocation entries for each module in the library need to be
    * accessed efficiently.  Since the relocation entries can't be accessed
    * through the section headers for a library file they are separated into
    * groups of local and external entries further grouped by module.  In this
    * case the presents of this load command who's extreloff, nextrel,
    * locreloff and nlocrel fields are non-zero indicates that the relocation
    * entries of non-merged sections are not referenced through the section
    * structures (and the reloff and nreloc fields in the section headers are
    * set to zero).
    *
    * Since the relocation entries are not accessed through the section headers
    * this requires the r_address field to be something other than a section
    * offset to identify the item to be relocated.  In this case r_address is
    * set to the offset from the vmaddr of the first LC_SEGMENT command.
    * For MH_SPLIT_SEGS images r_address is set to the the offset from the
    * vmaddr of the first read-write LC_SEGMENT command.
    *
    * The relocation entries are grouped by module and the module table
    * entries have indexes and counts into them for the group of external
    * relocation entries for that the module.
    *
    * For sections that are merged across modules there must not be any
    * remaining external relocation entries for them (for merged sections
    * remaining relocation entries must be local).
    */
    TYP(extreloff,4); /* offset to external relocation entries */
    TYP(nextrel,4); /* number of external relocation entries */

    /*
    * All the local relocation entries are grouped together (they are not
    * grouped by their module since they are only used if the object is moved
    * from it staticly link edited address).
    */
    TYP(locreloff,4); /* offset to local relocation entries */
    TYP(nlocrel,4); /* number of local relocation entries */
};

/*
* An indirect symbol table entry is simply a 32bit index into the symbol table
* to the symbol that the pointer or stub is refering to.  Unless it is for a
* non-lazy symbol pointer section for a defined symbol which strip(1) as
* removed.  In which case it has the value INDIRECT_SYMBOL_LOCAL.  If the
* symbol was also absolute INDIRECT_SYMBOL_ABS is or'ed with that.
*/
#define INDIRECT_SYMBOL_LOCAL    0x80000000
#define INDIRECT_SYMBOL_ABS    0x40000000


/* a table of contents entry */
struct dylib_table_of_contents {
    TYP(symbol_index,4); /* the defined external symbol
        (index into the symbol table) */
    TYP(module_index,4); /* index into the module table this symbol
        is defined in */
};

/* a module table entry */
struct dylib_module {
    TYP(module_name,4); /* the module name (index into string table) */

    TYP(iextdefsym,4); /* index into externally defined symbols */
    TYP(nextdefsym,4); /* number of externally defined symbols */
    TYP(irefsym,4); /* index into reference symbol table */
    TYP(nrefsym,4); /* number of reference symbol table entries */
    TYP(ilocalsym,4); /* index into symbols for local symbols */
    TYP(nlocalsym,4); /* number of local symbols */

    TYP(iextrel,4); /* index into external relocation entries */
    TYP(nextrel,4); /* number of external relocation entries */

    TYP(iinit_iterm,4); /* low 16 bits are the index into the init
        section, high 16 bits are the index into
        the term section */
    TYP(ninit_nterm,4); /* low 16 bits are the number of init section
        entries, high 16 bits are the number of
        term section entries */

    /* for this module address of the start of */
    /*  the (__OBJC,__module_info) section */
    TYP(objc_module_info_addr,4);

    /* for this module size of */
    /*  the (__OBJC,__module_info) section */
    TYP(objc_module_info_size,4);
};

/* a 64-bit module table entry */
struct dylib_module_64 {
    TYP(module_name,4); /* the module name (index into string table) */

    TYP(iextdefsym,4); /* index into externally defined symbols */
    TYP(nextdefsym,4); /* number of externally defined symbols */
    TYP(irefsym,4); /* index into reference symbol table */
    TYP(nrefsym,4); /* number of reference symbol table entries */
    TYP(ilocalsym,4); /* index into symbols for local symbols */
    TYP(nlocalsym,4); /* number of local symbols */

    TYP(iextrel,4); /* index into external relocation entries */
    TYP(nextrel,4); /* number of external relocation entries */

    TYP(iinit_iterm,4); /* low 16 bits are the index into the init
        section, high 16 bits are the index into
        the term section */
    TYP(ninit_nterm,4); /* low 16 bits are the number of init section
        entries, high 16 bits are the number of
        term section entries */

    TYP(objc_module_info_size,4); /* for this module size of */
        /*  the (__OBJC,__module_info) section */
    TYP(objc_module_info_addr,8); /* for this module address of the start of */
        /*  the (__OBJC,__module_info) section */
};

/*
* The entries in the reference symbol table are used when loading the module
* (both by the static and dynamic link editors) and if the module is unloaded
* or replaced.  Therefore all external symbols (defined and undefined) are
* listed in the module's reference table.  The flags describe the type of
* reference that is being made.  The constants for the flags are defined in
* <mach-o/nlist.h> as they are also used for symbol table entries.
*/
#if 0 /* dwarf readers not using this */
struct dylib_reference {
    UNUSED uint32_t isym:24,        /* index into the symbol table */
    UNUSED flags:8;    /* flags to indicate the type of reference */
};
#endif /* 0 */

/*
* The twolevel_hints_command contains the offset and number of hints in the
* two-level namespace lookup hints table.
*/
struct twolevel_hints_command {
    TYP(cmd,4); /* LC_TWOLEVEL_HINTS */
    TYP(cmdsize,4); /* sizeof(struct twolevel_hints_command) */
    TYP(offset,4); /* offset to the hint table */
    TYP(nhints,4); /* number of hints in the hint table */
};

/*
* The entries in the two-level namespace lookup hints table are twolevel_hint
* structs.  These provide hints to the dynamic link editor where to start
* looking for an undefined symbol in a two-level namespace image.  The
* isub_image field is an index into the sub-images (sub-frameworks and
* sub-umbrellas list) that made up the two-level image that the undefined
* symbol was found in when it was built by the static link editor.  If
* isub-image is 0 the the symbol is expected to be defined in library and not
* in the sub-images.  If isub-image is non-zero it is an index into the array
* of sub-images for the umbrella with the first index in the sub-images being
* 1. The array of sub-images is the ordered list of sub-images of the umbrella
* that would be searched for a symbol that has the umbrella recorded as its
* primary library.  The table of contents index is an index into the
* library's table of contents.  This is used as the starting point of the
* binary search or a directed linear search.
*/
#if 0
/* Not used by dwarf readers. */
struct twolevel_hint {
    UNUSED uint32_t
    isub_image:8,    /* index into the sub images */
    itoc:24;    /* index into the table of contents */
};
#endif

/*
* The prebind_cksum_command contains the value of the original check sum for
* prebound files or zero.  When a prebound file is first created or modified
* for other than updating its prebinding information the value of the check sum
* is set to zero.  When the file has it prebinding re-done and if the value of
* the check sum is zero the original check sum is calculated and stored in
* cksum field of this load command in the output file.  If when the prebinding
* is re-done and the cksum field is non-zero it is left unchanged from the
* input file.
*/
struct prebind_cksum_command {
    TYP(cmd,4); /* LC_PREBIND_CKSUM */
    TYP(cmdsize,4); /* sizeof(struct prebind_cksum_command) */
    TYP(cksum,4); /* the check sum or zero */
};

/*
* The uuid load command contains a single 128-bit unique random number that
* identifies an object produced by the static link editor.
*/
struct uuid_command {
    TYP(cmd,4); /* LC_UUID */
    TYP(cmdsize,4); /* sizeof(struct uuid_command) */
    unsigned char uuid[16];    /* the 128-bit uuid */
};

/*
* The rpath_command contains a path which at runtime should be added to
* the current run path used to find @rpath prefixed dylibs.
*/
struct rpath_command {
    TYP(cmd,4); /* LC_RPATH */
    TYP(cmdsize,4); /* includes string */
    union lc_str path;        /* path to add to run path */
};

/*
* The linkedit_data_command contains the offsets and sizes of a blob
* of data in the __LINKEDIT segment.
*/
struct linkedit_data_command {
    TYP(cmd,4); /* LC_CODE_SIGNATURE, LC_SEGMENT_SPLIT_INFO,
        LC_FUNCTION_STARTS, LC_DATA_IN_CODE,
        LC_DYLIB_CODE_SIGN_DRS or
        LC_LINKER_OPTIMIZATION_HINT. */
    TYP(cmdsize,4); /* sizeof(struct linkedit_data_command) */
    TYP(dataoff,4); /* file offset of data in __LINKEDIT segment */
    TYP(datasize,4); /* file size of data in __LINKEDIT segment */
};

/*
* The encryption_info_command contains the file offset and size of an
* of an encrypted segment.
*/
struct encryption_info_command {
    TYP(cmd,4); /* LC_ENCRYPTION_INFO */
    TYP(cmdsize,4); /* sizeof(struct encryption_info_command) */
    TYP(cryptoff,4); /* file offset of encrypted range */
    TYP(cryptsize,4); /* file size of encrypted range */
    TYP(cryptid,4); /* which enryption system,
        0 means not-encrypted yet */
};

/*
* The encryption_info_command_64 contains the file offset and size of an
* of an encrypted segment (for use in x86_64 targets).
*/
struct encryption_info_command_64 {
    TYP(cmd,4); /* LC_ENCRYPTION_INFO_64 */
    TYP(cmdsize,4); /* sizeof(struct encryption_info_command_64) */
    TYP(cryptoff,4); /* file offset of encrypted range */
    TYP(cryptsize,4); /* file size of encrypted range */
    TYP(cryptid,4); /* which enryption system,
        0 means not-encrypted yet */
    TYP(pad,4); /* padding to make this struct's size a multiple
        of 8 bytes */
};

/*
* The version_min_command contains the min OS version on which this
* binary was built to run.
*/
struct version_min_command {
    TYP(cmd,4); /* LC_VERSION_MIN_MACOSX or
        LC_VERSION_MIN_IPHONEOS or
        LC_VERSION_MIN_WATCHOS or
        LC_VERSION_MIN_TVOS */
    TYP(cmdsize,4); /* sizeof(struct min_version_command) */
    TYP(version,4); /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
    TYP(sdk,4); /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
};

/*
* The dyld_info_command contains the file offsets and sizes of
* the new compressed form of the information dyld needs to
* load the image.  This information is used by dyld on Mac OS X
* 10.6 and later.  All information pointed to by this command
* is encoded using byte streams, so no endian swapping is needed
* to interpret it.
*/
struct dyld_info_command {
    TYP(cmd,4); /* LC_DYLD_INFO or LC_DYLD_INFO_ONLY */
    TYP(cmdsize,4); /* sizeof(struct dyld_info_command) */

    /*
    * Dyld rebases an image whenever dyld loads it at an address different
    * from its preferred address.  The rebase information is a stream
    * of byte sized opcodes whose symbolic names start with REBASE_OPCODE_.
    * Conceptually the rebase information is a table of tuples:
    *    <seg-index, seg-offset, type>
    * The opcodes are a compressed way to encode the table by only
    * encoding when a column changes.  In addition simple patterns
    * like "every n'th offset for m times" can be encoded in a few
    * bytes.
    */
    TYP(rebase_off,4); /* file offset to rebase info */
    TYP(rebase_size,4); /* size of rebase info */

    /*
    * Dyld binds an image during the loading process, if the image
    * requires any pointers to be initialized to symbols in other images.
    * The bind information is a stream of byte sized
    * opcodes whose symbolic names start with BIND_OPCODE_.
    * Conceptually the bind information is a table of tuples:
    *    <seg-index, seg-offset, type, symbol-library-ordinal, symbol-name, addend>
    * The opcodes are a compressed way to encode the table by only
    * encoding when a column changes.  In addition simple patterns
    * like for runs of pointers initialzed to the same value can be
    * encoded in a few bytes.
    */
    TYP(bind_off,4); /* file offset to binding info */
    TYP(bind_size,4); /* size of binding info */

    /*
    * Some C++ programs require dyld to unique symbols so that all
    * images in the process use the same copy of some code/data.
    * This step is done after binding. The content of the weak_bind
    * info is an opcode stream like the bind_info.  But it is sorted
    * alphabetically by symbol name.  This enable dyld to walk
    * all images with weak binding information in order and look
    * for collisions.  If there are no collisions, dyld does
    * no updating.  That means that some fixups are also encoded
    * in the bind_info.  For instance, all calls to "operator new"
    * are first bound to libstdc++.dylib using the information
    * in bind_info.  Then if some image overrides operator new
    * that is detected when the weak_bind information is processed
    * and the call to operator new is then rebound.
    */
    TYP(weak_bind_off,4); /* file offset to weak binding info */
    TYP(weak_bind_size,4); /* size of weak binding info */

    /*
    * Some uses of external symbols do not need to be bound immediately.
    * Instead they can be lazily bound on first use.  The lazy_bind
    * are contains a stream of BIND opcodes to bind all lazy symbols.
    * Normal use is that dyld ignores the lazy_bind section when
    * loading an image.  Instead the static linker arranged for the
    * lazy pointer to initially point to a helper function which
    * pushes the offset into the lazy_bind area for the symbol
    * needing to be bound, then jumps to dyld which simply adds
    * the offset to lazy_bind_off to get the information on what
    * to bind.
    */
    TYP(lazy_bind_off,4); /* file offset to lazy binding info */
    TYP(lazy_bind_size,4); /* size of lazy binding infs */

    /*
    * The symbols exported by a dylib are encoded in a trie.  This
    * is a compact representation that factors out common prefixes.
    * It also reduces LINKEDIT pages in RAM because it encodes all
    * information (name, address, flags) in one small, contiguous range.
    * The export area is a stream of nodes.  The first node sequentially
    * is the start node for the trie.
    *
    * Nodes for a symbol start with a uleb128 that is the length of
    * the exported symbol information for the string so far.
    * If there is no exported symbol, the node starts with a zero byte.
    * If there is exported info, it follows the length.
    *
    * First is a uleb128 containing flags. Normally, it is followed by
    * a uleb128 encoded offset which is location of the content named
    * by the symbol from the mach_header for the image.  If the flags
    * is EXPORT_SYMBOL_FLAGS_REEXPORT, then following the flags is
    * a uleb128 encoded library ordinal, then a zero terminated
    * UTF8 string.  If the string is zero length, then the symbol
    * is re-export from the specified dylib with the same name.
    * If the flags is EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER, then following
    * the flags is two uleb128s: the stub offset and the resolver offset.
    * The stub is used by non-lazy pointers.  The resolver is used
    * by lazy pointers and must be called to get the actual address to use.
    *
    * After the optional exported symbol information is a byte of
    * how many edges (0-255) that this node has leaving it,
    * followed by each edge.
    * Each edge is a zero terminated UTF8 of the addition chars
    * in the symbol, followed by a uleb128 offset for the node that
    * edge points to.
    *
    */
    TYP(export_off,4); /* file offset to lazy binding info */
    TYP(export_size,4); /* size of lazy binding infs */
};

/*
* The following are used to encode rebasing information
*/
#define REBASE_TYPE_POINTER                    1
#define REBASE_TYPE_TEXT_ABSOLUTE32                2
#define REBASE_TYPE_TEXT_PCREL32                3

#define REBASE_OPCODE_MASK                    0xF0
#define REBASE_IMMEDIATE_MASK                    0x0F
#define REBASE_OPCODE_DONE                    0x00
#define REBASE_OPCODE_SET_TYPE_IMM                0x10
#define REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB        0x20
#define REBASE_OPCODE_ADD_ADDR_ULEB                0x30
#define REBASE_OPCODE_ADD_ADDR_IMM_SCALED            0x40
#define REBASE_OPCODE_DO_REBASE_IMM_TIMES            0x50
#define REBASE_OPCODE_DO_REBASE_ULEB_TIMES            0x60
#define REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB            0x70
#define REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB    0x80


/*
* The following are used to encode binding information
*/
#define BIND_TYPE_POINTER                    1
#define BIND_TYPE_TEXT_ABSOLUTE32                2
#define BIND_TYPE_TEXT_PCREL32                    3

#define BIND_SPECIAL_DYLIB_SELF                     0
#define BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE            -1
#define BIND_SPECIAL_DYLIB_FLAT_LOOKUP                -2

#define BIND_SYMBOL_FLAGS_WEAK_IMPORT                0x1
#define BIND_SYMBOL_FLAGS_NON_WEAK_DEFINITION            0x8

#define BIND_OPCODE_MASK                    0xF0
#define BIND_IMMEDIATE_MASK                    0x0F
#define BIND_OPCODE_DONE                    0x00
#define BIND_OPCODE_SET_DYLIB_ORDINAL_IMM            0x10
#define BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB            0x20
#define BIND_OPCODE_SET_DYLIB_SPECIAL_IMM            0x30
#define BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM        0x40
#define BIND_OPCODE_SET_TYPE_IMM                0x50
#define BIND_OPCODE_SET_ADDEND_SLEB                0x60
#define BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB            0x70
#define BIND_OPCODE_ADD_ADDR_ULEB                0x80
#define BIND_OPCODE_DO_BIND                    0x90
#define BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB            0xA0
#define BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED            0xB0
#define BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB        0xC0


/*
* The following are used on the flags byte of a terminal node
* in the export information.
*/
#define EXPORT_SYMBOL_FLAGS_KIND_MASK                0x03
#define EXPORT_SYMBOL_FLAGS_KIND_REGULAR            0x00
#define EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL            0x01
#define EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION            0x04
#define EXPORT_SYMBOL_FLAGS_REEXPORT                0x08
#define EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER            0x10

/*
* The linker_option_command contains linker options embedded in object files.
*/
struct linker_option_command {
    TYP(cmd,4); /* LC_LINKER_OPTION only used in MH_OBJECT filetypes */
    TYP(cmdsize,4);
    TYP(count,4); /* number of strings */
    /* concatenation of zero terminated UTF8 strings.
        Zero filled at end to align */
};

/*
* The symseg_command contains the offset and size of the GNU style
* symbol table information as described in the header file <symseg.h>.
* The symbol roots of the symbol segments must also be aligned properly
* in the file.  So the requirement of keeping the offsets aligned to a
* multiple of a 4 bytes translates to the length field of the symbol
* roots also being a multiple of a long.  Also the padding must again be
* zeroed. (THIS IS OBSOLETE and no longer supported).
*/
struct symseg_command {
    TYP(cmd,4); /* LC_SYMSEG */
    TYP(cmdsize,4); /* sizeof(struct symseg_command) */
    TYP(offset,4); /* symbol segment offset */
    TYP(size,4); /* symbol segment size in bytes */
};

/*
* The ident_command contains a free format string table following the
* ident_command structure.  The strings are null terminated and the size of
* the command is padded out with zero bytes to a multiple of 4 bytes/
* (THIS IS OBSOLETE and no longer supported).
*/
struct ident_command {
    TYP(cmd,4); /* LC_IDENT */
    TYP(cmdsize,4); /* strings that follow this command */
};

/*
* The fvmfile_command contains a reference to a file to be loaded at the
* specified virtual address.  (Presently, this command is reserved for
* internal use.  The kernel ignores this command when loading a program into
* memory).
*/
struct fvmfile_command {
    TYP(cmd,4); /* LC_FVMFILE */
    TYP(cmdsize,4); /* includes pathname string */
    union lc_str    name;        /* files pathname */
    TYP(header_addr,4); /* files virtual address */
};


/*
* The entry_point_command is a replacement for thread_command.
* It is used for main executables to specify the location (file offset)
* of main().  If -stack_size was used at link time, the stacksize
* field will contain the stack size need for the main thread.
*/
struct entry_point_command {
    TYP(cmd,4); /* LC_MAIN only used in MH_EXECUTE filetypes */
    TYP(cmdsize,4); /* 24 */
    TYP(entryoff,8); /* file (__TEXT) offset of main() */
    TYP(stacksize,8); /* if not zero, initial stack size */
};


/*
* The source_version_command is an optional load command containing
* the version of the sources used to build the binary.
*/
struct source_version_command {
    TYP(cmd,4); /* LC_SOURCE_VERSION */
    TYP(cmdsize,4); /* 16 */
    TYP(version,8); /* A.B.C.D.E packed as a24.b10.c10.d10.e10 */
};


/*
* The LC_DATA_IN_CODE load commands uses a linkedit_data_command
* to point to an array of data_in_code_entry entries. Each entry
* describes a range of data in a code section.
*/
struct data_in_code_entry {
    TYP(offset,4); /* from mach_header to start of data range*/
    TYP(length,2); /* number of bytes in data range */
    TYP(kind,2); /* a DICE_KIND_* value */
};
#define DICE_KIND_DATA              0x0001
#define DICE_KIND_JUMP_TABLE8       0x0002
#define DICE_KIND_JUMP_TABLE16      0x0003
#define DICE_KIND_JUMP_TABLE32      0x0004
#define DICE_KIND_ABS_JUMP_TABLE32  0x0005



/*
* Sections of type S_THREAD_LOCAL_VARIABLES contain an array
* of tlv_descriptor structures.
*/
struct tlv_descriptor
{
    void*          (*thunk)(struct tlv_descriptor*);
    unsigned long  key;
    unsigned long  offset;
};
#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif /* MACHO_LOADER_H */