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1.1 root 1: /*
2: * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
3: *
4: * @APPLE_LICENSE_HEADER_START@
5: *
6: * The contents of this file constitute Original Code as defined in and
7: * are subject to the Apple Public Source License Version 1.1 (the
8: * "License"). You may not use this file except in compliance with the
9: * License. Please obtain a copy of the License at
10: * http://www.apple.com/publicsource and read it before using this file.
11: *
12: * This Original Code and all software distributed under the License are
13: * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
14: * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
15: * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
16: * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
17: * License for the specific language governing rights and limitations
18: * under the License.
19: *
20: * @APPLE_LICENSE_HEADER_END@
21: */
22: #ifndef _MACHO_LOADER_H_
23: #define _MACHO_LOADER_H_
24:
25: /*
26: * This file describes the format of mach object files.
27: */
28:
29: /*
30: * <mach/machine.h> is needed here for the cpu_type_t and cpu_subtype_t types
31: * and contains the constants for the possible values of these types.
32: */
33: #import <mach/machine.h>
34:
35: /*
36: * <mach/vm_prot.h> is needed here for the vm_prot_t type and contains the
37: * constants that are or'ed together for the possible values of this type.
38: */
39: #import <mach/vm_prot.h>
40:
41: /*
42: * <machine/thread_status.h> is expected to define the flavors of the thread
43: * states and the structures of those flavors for each machine.
44: */
45: #import <mach/machine/thread_status.h>
46: #import <architecture/byte_order.h>
47:
48: /*
49: * The mach header appears at the very beginning of the object file.
50: */
51: struct mach_header {
52: unsigned long magic; /* mach magic number identifier */
53: cpu_type_t cputype; /* cpu specifier */
54: cpu_subtype_t cpusubtype; /* machine specifier */
55: unsigned long filetype; /* type of file */
56: unsigned long ncmds; /* number of load commands */
57: unsigned long sizeofcmds; /* the size of all the load commands */
58: unsigned long flags; /* flags */
59: };
60:
61: /* Constant for the magic field of the mach_header */
62: #define MH_MAGIC 0xfeedface /* the mach magic number */
63: #define MH_CIGAM NXSwapInt(MH_MAGIC)
64:
65: /*
66: * The layout of the file depends on the filetype. For all but the MH_OBJECT
67: * file type the segments are padded out and aligned on a segment alignment
68: * boundary for efficient demand pageing. The MH_EXECUTE, MH_FVMLIB, MH_DYLIB,
69: * MH_DYLINKER and MH_BUNDLE file types also have the headers included as part
70: * of their first segment.
71: *
72: * The file type MH_OBJECT is a compact format intended as output of the
73: * assembler and input (and possibly output) of the link editor (the .o
74: * format). All sections are in one unnamed segment with no segment padding.
75: * This format is used as an executable format when the file is so small the
76: * segment padding greatly increases it's size.
77: *
78: * The file type MH_PRELOAD is an executable format intended for things that
79: * not executed under the kernel (proms, stand alones, kernels, etc). The
80: * format can be executed under the kernel but may demand paged it and not
81: * preload it before execution.
82: *
83: * A core file is in MH_CORE format and can be any in an arbritray legal
84: * Mach-O file.
85: *
86: * Constants for the filetype field of the mach_header
87: */
88: #define MH_OBJECT 0x1 /* relocatable object file */
89: #define MH_EXECUTE 0x2 /* demand paged executable file */
90: #define MH_FVMLIB 0x3 /* fixed VM shared library file */
91: #define MH_CORE 0x4 /* core file */
92: #define MH_PRELOAD 0x5 /* preloaded executable file */
93: #define MH_DYLIB 0x6 /* dynamicly bound shared library file*/
94: #define MH_DYLINKER 0x7 /* dynamic link editor */
95: #define MH_BUNDLE 0x8 /* dynamicly bound bundle file */
96:
97: /* Constants for the flags field of the mach_header */
98: #define MH_NOUNDEFS 0x1 /* the object file has no undefined
99: references, can be executed */
100: #define MH_INCRLINK 0x2 /* the object file is the output of an
101: incremental link against a base file
102: and can't be link edited again */
103: #define MH_DYLDLINK 0x4 /* the object file is input for the
104: dynamic linker and can't be staticly
105: link edited again */
106: #define MH_BINDATLOAD 0x8 /* the object file's undefined
107: references are bound by the dynamic
108: linker when loaded. */
109: #define MH_PREBOUND 0x10 /* the file has it's dynamic undefined
110: references prebound. */
111:
112: /*
113: * The load commands directly follow the mach_header. The total size of all
114: * of the commands is given by the sizeofcmds field in the mach_header. All
115: * load commands must have as their first two fields cmd and cmdsize. The cmd
116: * field is filled in with a constant for that command type. Each command type
117: * has a structure specifically for it. The cmdsize field is the size in bytes
118: * of the particular load command structure plus anything that follows it that
119: * is a part of the load command (i.e. section structures, strings, etc.). To
120: * advance to the next load command the cmdsize can be added to the offset or
121: * pointer of the current load command. The cmdsize MUST be a multiple of
122: * sizeof(long) (this is forever the maximum alignment of any load commands).
123: * The padded bytes must be zero. All tables in the object file must also
124: * follow these rules so the file can be memory mapped. Otherwise the pointers
125: * to these tables will not work well or at all on some machines. With all
126: * padding zeroed like objects will compare byte for byte.
127: */
128: struct load_command {
129: unsigned long cmd; /* type of load command */
130: unsigned long cmdsize; /* total size of command in bytes */
131: };
132:
133: /* Constants for the cmd field of all load commands, the type */
134: #define LC_SEGMENT 0x1 /* segment of this file to be mapped */
135: #define LC_SYMTAB 0x2 /* link-edit stab symbol table info */
136: #define LC_SYMSEG 0x3 /* link-edit gdb symbol table info (obsolete) */
137: #define LC_THREAD 0x4 /* thread */
138: #define LC_UNIXTHREAD 0x5 /* unix thread (includes a stack) */
139: #define LC_LOADFVMLIB 0x6 /* load a specified fixed VM shared library */
140: #define LC_IDFVMLIB 0x7 /* fixed VM shared library identification */
141: #define LC_IDENT 0x8 /* object identification info (obsolete) */
142: #define LC_FVMFILE 0x9 /* fixed VM file inclusion (internal use) */
143: #define LC_PREPAGE 0xa /* prepage command (internal use) */
144: #define LC_DYSYMTAB 0xb /* dynamic link-edit symbol table info */
145: #define LC_LOAD_DYLIB 0xc /* load a dynamicly linked shared library */
146: #define LC_ID_DYLIB 0xd /* dynamicly linked shared lib identification */
147: #define LC_LOAD_DYLINKER 0xe /* load a dynamic linker */
148: #define LC_ID_DYLINKER 0xf /* dynamic linker identification */
149: #define LC_PREBOUND_DYLIB 0x10 /* modules prebound for a dynamicly */
150: /* linked shared library */
151:
152: /*
153: * A variable length string in a load command is represented by an lc_str
154: * union. The strings are stored just after the load command structure and
155: * the offset is from the start of the load command structure. The size
156: * of the string is reflected in the cmdsize field of the load command.
157: * Once again any padded bytes to bring the cmdsize field to a multiple
158: * of sizeof(long) must be zero.
159: */
160: union lc_str {
161: unsigned long offset; /* offset to the string */
162: char *ptr; /* pointer to the string */
163: };
164:
165: /*
166: * The segment load command indicates that a part of this file is to be
167: * mapped into the task's address space. The size of this segment in memory,
168: * vmsize, maybe equal to or larger than the amount to map from this file,
169: * filesize. The file is mapped starting at fileoff to the beginning of
170: * the segment in memory, vmaddr. The rest of the memory of the segment,
171: * if any, is allocated zero fill on demand. The segment's maximum virtual
172: * memory protection and initial virtual memory protection are specified
173: * by the maxprot and initprot fields. If the segment has sections then the
174: * section structures directly follow the segment command and their size is
175: * reflected in cmdsize.
176: */
177: struct segment_command {
178: unsigned long cmd; /* LC_SEGMENT */
179: unsigned long cmdsize; /* includes sizeof section structs */
180: char segname[16]; /* segment name */
181: unsigned long vmaddr; /* memory address of this segment */
182: unsigned long vmsize; /* memory size of this segment */
183: unsigned long fileoff; /* file offset of this segment */
184: unsigned long filesize; /* amount to map from the file */
185: vm_prot_t maxprot; /* maximum VM protection */
186: vm_prot_t initprot; /* initial VM protection */
187: unsigned long nsects; /* number of sections in segment */
188: unsigned long flags; /* flags */
189: };
190:
191: /* Constants for the flags field of the segment_command */
192: #define SG_HIGHVM 0x1 /* the file contents for this segment is for
193: the high part of the VM space, the low part
194: is zero filled (for stacks in core files) */
195: #define SG_FVMLIB 0x2 /* this segment is the VM that is allocated by
196: a fixed VM library, for overlap checking in
197: the link editor */
198: #define SG_NORELOC 0x4 /* this segment has nothing that was relocated
199: in it and nothing relocated to it, that is
200: it maybe safely replaced without relocation*/
201:
202: /*
203: * A segment is made up of zero or more sections. Non-MH_OBJECT files have
204: * all of their segments with the proper sections in each, and padded to the
205: * specified segment alignment when produced by the link editor. The first
206: * segment of a MH_EXECUTE and MH_FVMLIB format file contains the mach_header
207: * and load commands of the object file before it's first section. The zero
208: * fill sections are always last in their segment (in all formats). This
209: * allows the zeroed segment padding to be mapped into memory where zero fill
210: * sections might be.
211: *
212: * The MH_OBJECT format has all of it's sections in one segment for
213: * compactness. There is no padding to a specified segment boundary and the
214: * mach_header and load commands are not part of the segment.
215: *
216: * Sections with the same section name, sectname, going into the same segment,
217: * segname, are combined by the link editor. The resulting section is aligned
218: * to the maximum alignment of the combined sections and is the new section's
219: * alignment. The combined sections are aligned to their original alignment in
220: * the combined section. Any padded bytes to get the specified alignment are
221: * zeroed.
222: *
223: * The format of the relocation entries referenced by the reloff and nreloc
224: * fields of the section structure for mach object files is described in the
225: * header file <reloc.h>.
226: */
227: struct section {
228: char sectname[16]; /* name of this section */
229: char segname[16]; /* segment this section goes in */
230: unsigned long addr; /* memory address of this section */
231: unsigned long size; /* size in bytes of this section */
232: unsigned long offset; /* file offset of this section */
233: unsigned long align; /* section alignment (power of 2) */
234: unsigned long reloff; /* file offset of relocation entries */
235: unsigned long nreloc; /* number of relocation entries */
236: unsigned long flags; /* flags (section type and attributes)*/
237: unsigned long reserved1; /* reserved */
238: unsigned long reserved2; /* reserved */
239: };
240:
241: /*
242: * The flags field of a section structure is separated into two parts a section
243: * type and section attributes. The section types are mutually exclusive (it
244: * can only have one type) but the section attributes are not (it may have more
245: * than one attribute).
246: */
247: #define SECTION_TYPE 0x000000ff /* 256 section types */
248: #define SECTION_ATTRIBUTES 0xffffff00 /* 24 section attributes */
249:
250: /* Constants for the type of a section */
251: #define S_REGULAR 0x0 /* regular section */
252: #define S_ZEROFILL 0x1 /* zero fill on demand section */
253: #define S_CSTRING_LITERALS 0x2 /* section with only literal C strings*/
254: #define S_4BYTE_LITERALS 0x3 /* section with only 4 byte literals */
255: #define S_8BYTE_LITERALS 0x4 /* section with only 8 byte literals */
256: #define S_LITERAL_POINTERS 0x5 /* section with only pointers to */
257: /* literals */
258: /*
259: * For the two types of symbol pointers sections and the symbol stubs section
260: * they have indirect symbol table entries. For each of the entries in the
261: * section the indirect symbol table entries, in corresponding order in the
262: * indirect symbol table, start at the index stored in the reserved1 field
263: * of the section structure. Since the indirect symbol table entries
264: * correspond to the entries in the section the number of indirect symbol table
265: * entries is inferred from the size of the section divided by the size of the
266: * entries in the section. For symbol pointers sections the size of the entries
267: * in the section is 4 bytes and for symbol stubs sections the byte size of the
268: * stubs is stored in the reserved2 field of the section structure.
269: */
270: #define S_NON_LAZY_SYMBOL_POINTERS 0x6 /* section with only non-lazy
271: symbol pointers */
272: #define S_LAZY_SYMBOL_POINTERS 0x7 /* section with only lazy symbol
273: pointers */
274: #define S_SYMBOL_STUBS 0x8 /* section with only symbol
275: stubs, byte size of stub in
276: the reserved2 field */
277: #define S_MOD_INIT_FUNC_POINTERS 0x9 /* section with only function
278: pointers for initialization*/
279: /*
280: * Constants for the section attributes part of the flags field of a section
281: * structure.
282: */
283: #define SECTION_ATTRIBUTES_USR 0xff000000 /* User setable attributes */
284: #define S_ATTR_PURE_INSTRUCTIONS 0x80000000 /* section contains only true
285: machine instructions */
286: #define SECTION_ATTRIBUTES_SYS 0x00ffff00 /* system setable attributes */
287: #define S_ATTR_SOME_INSTRUCTIONS 0x00000400 /* section contains some
288: machine instructions */
289: #define S_ATTR_EXT_RELOC 0x00000200 /* section has external
290: relocation entries */
291: #define S_ATTR_LOC_RELOC 0x00000100 /* section has local
292: relocation entries */
293:
294:
295: /*
296: * The names of segments and sections in them are mostly meaningless to the
297: * link-editor. But there are few things to support traditional UNIX
298: * executables that require the link-editor and assembler to use some names
299: * agreed upon by convention.
300: *
301: * The initial protection of the "__TEXT" segment has write protection turned
302: * off (not writeable).
303: *
304: * The link-editor will allocate common symbols at the end of the "__common"
305: * section in the "__DATA" segment. It will create the section and segment
306: * if needed.
307: */
308:
309: /* The currently known segment names and the section names in those segments */
310:
311: #define SEG_PAGEZERO "__PAGEZERO" /* the pagezero segment which has no */
312: /* protections and catches NULL */
313: /* references for MH_EXECUTE files */
314:
315:
316: #define SEG_TEXT "__TEXT" /* the tradition UNIX text segment */
317: #define SECT_TEXT "__text" /* the real text part of the text */
318: /* section no headers, and no padding */
319: #define SECT_FVMLIB_INIT0 "__fvmlib_init0" /* the fvmlib initialization */
320: /* section */
321: #define SECT_FVMLIB_INIT1 "__fvmlib_init1" /* the section following the */
322: /* fvmlib initialization */
323: /* section */
324:
325: #define SEG_DATA "__DATA" /* the tradition UNIX data segment */
326: #define SECT_DATA "__data" /* the real initialized data section */
327: /* no padding, no bss overlap */
328: #define SECT_BSS "__bss" /* the real uninitialized data section*/
329: /* no padding */
330: #define SECT_COMMON "__common" /* the section common symbols are */
331: /* allocated in by the link editor */
332:
333: #define SEG_OBJC "__OBJC" /* objective-C runtime segment */
334: #define SECT_OBJC_SYMBOLS "__symbol_table" /* symbol table */
335: #define SECT_OBJC_MODULES "__module_info" /* module information */
336: #define SECT_OBJC_STRINGS "__selector_strs" /* string table */
337: #define SECT_OBJC_REFS "__selector_refs" /* string table */
338:
339: #define SEG_ICON "__ICON" /* the NeXT icon segment */
340: #define SECT_ICON_HEADER "__header" /* the icon headers */
341: #define SECT_ICON_TIFF "__tiff" /* the icons in tiff format */
342:
343: #define SEG_LINKEDIT "__LINKEDIT" /* the segment containing all structs */
344: /* created and maintained by the link */
345: /* editor. Created with -seglinkedit */
346: /* option to ld(1) for MH_EXECUTE and */
347: /* FVMLIB file types only */
348:
349: #define SEG_UNIXSTACK "__UNIXSTACK" /* the unix stack segment */
350:
351: /*
352: * Fixed virtual memory shared libraries are identified by two things. The
353: * target pathname (the name of the library as found for execution), and the
354: * minor version number. The address of where the headers are loaded is in
355: * header_addr.
356: */
357: struct fvmlib {
358: union lc_str name; /* library's target pathname */
359: unsigned long minor_version; /* library's minor version number */
360: unsigned long header_addr; /* library's header address */
361: };
362:
363: /*
364: * A fixed virtual shared library (filetype == MH_FVMLIB in the mach header)
365: * contains a fvmlib_command (cmd == LC_IDFVMLIB) to identify the library.
366: * An object that uses a fixed virtual shared library also contains a
367: * fvmlib_command (cmd == LC_LOADFVMLIB) for each library it uses.
368: */
369: struct fvmlib_command {
370: unsigned long cmd; /* LC_IDFVMLIB or LC_LOADFVMLIB */
371: unsigned long cmdsize; /* includes pathname string */
372: struct fvmlib fvmlib; /* the library identification */
373: };
374:
375: /*
376: * Dynamicly linked shared libraries are identified by two things. The
377: * pathname (the name of the library as found for execution), and the
378: * compatibility version number. The pathname must match and the compatibility
379: * number in the user of the library must be greater than or equal to the
380: * library being used. The time stamp is used to record the time a library was
381: * built and copied into user so it can be use to determined if the library used
382: * at runtime is exactly the same as used to built the program.
383: */
384: struct dylib {
385: union lc_str name; /* library's path name */
386: unsigned long timestamp; /* library's build time stamp */
387: unsigned long current_version; /* library's current version number */
388: unsigned long compatibility_version;/* library's compatibility vers number*/
389: };
390:
391: /*
392: * A dynamicly linked shared library (filetype == MH_DYLIB in the mach header)
393: * contains a dylib_command (cmd == LC_ID_DYLIB) to identify the library.
394: * An object that uses a dynamicly linked shared library also contains a
395: * dylib_command (cmd == LC_LOAD_DYLIB) for each library it uses.
396: */
397: struct dylib_command {
398: unsigned long cmd; /* LC_ID_DYLIB or LC_LOAD_DYLIB */
399: unsigned long cmdsize; /* includes pathname string */
400: struct dylib dylib; /* the library identification */
401: };
402:
403: /*
404: * A program (filetype == MH_EXECUTE) or bundle (filetype == MH_BUNDLE) that is
405: * prebound to it's dynamic libraries has one of these for each library that
406: * the static linker used in prebinding. It contains a bit vector for the
407: * modules in the library. The bits indicate which modules are bound (1) and
408: * which are not (0) from the library. The bit for module 0 is the low bit
409: * of the first byte. So the bit for the Nth module is:
410: * (linked_modules[N/8] >> N%8) & 1
411: */
412: struct prebound_dylib_command {
413: unsigned long cmd; /* LC_PREBOUND_DYLIB */
414: unsigned long cmdsize; /* includes strings */
415: union lc_str name; /* library's path name */
416: unsigned long nmodules; /* number of modules in library */
417: union lc_str linked_modules; /* bit vector of linked modules */
418: };
419:
420: /*
421: * A program that uses a dynamic linker contains a dylinker_command to identify
422: * the name of the dynamic linker (LC_LOAD_DYLINKER). And a dynamic linker
423: * contains a dylinker_command to identify the dynamic linker (LC_ID_DYLINKER).
424: * A file can have at most one of these.
425: */
426: struct dylinker_command {
427: unsigned long cmd; /* LC_ID_DYLINKER or LC_LOAD_DYLINKER */
428: unsigned long cmdsize; /* includes pathname string */
429: union lc_str name; /* dynamic linker's path name */
430: };
431:
432: /*
433: * Thread commands contain machine-specific data structures suitable for
434: * use in the thread state primitives. The machine specific data structures
435: * follow the struct thread_command as follows.
436: * Each flavor of machine specific data structure is preceded by an unsigned
437: * long constant for the flavor of that data structure, an unsigned long
438: * that is the count of longs of the size of the state data structure and then
439: * the state data structure follows. This triple may be repeated for many
440: * flavors. The constants for the flavors, counts and state data structure
441: * definitions are expected to be in the header file <machine/thread_status.h>.
442: * These machine specific data structures sizes must be multiples of
443: * sizeof(long). The cmdsize reflects the total size of the thread_command
444: * and all of the sizes of the constants for the flavors, counts and state
445: * data structures.
446: *
447: * For executable objects that are unix processes there will be one
448: * thread_command (cmd == LC_UNIXTHREAD) created for it by the link-editor.
449: * This is the same as a LC_THREAD, except that a stack is automatically
450: * created (based on the shell's limit for the stack size). Command arguments
451: * and environment variables are copied onto that stack.
452: */
453: struct thread_command {
454: unsigned long cmd; /* LC_THREAD or LC_UNIXTHREAD */
455: unsigned long cmdsize; /* total size of this command */
456: /* unsigned long flavor flavor of thread state */
457: /* unsigned long count count of longs in thread state */
458: /* struct XXX_thread_state state thread state for this flavor */
459: /* ... */
460: };
461:
462: /*
463: * The symtab_command contains the offsets and sizes of the link-edit 4.3BSD
464: * "stab" style symbol table information as described in the header files
465: * <nlist.h> and <stab.h>.
466: */
467: struct symtab_command {
468: unsigned long cmd; /* LC_SYMTAB */
469: unsigned long cmdsize; /* sizeof(struct symtab_command) */
470: unsigned long symoff; /* symbol table offset */
471: unsigned long nsyms; /* number of symbol table entries */
472: unsigned long stroff; /* string table offset */
473: unsigned long strsize; /* string table size in bytes */
474: };
475:
476: /*
477: * This is the second set of the symbolic information which is used to support
478: * the data structures for the dynamicly link editor.
479: *
480: * The original set of symbolic information in the symtab_command which contains
481: * the symbol and string tables must also be present when this load command is
482: * present. When this load command is present the symbol table is organized
483: * into three groups of symbols:
484: * local symbols (static and debugging symbols) - grouped by module
485: * defined external symbols - grouped by module (sorted by name if not lib)
486: * undefined external symbols (sorted by name)
487: * In this load command there are offsets and counts to each of the three groups
488: * of symbols.
489: *
490: * This load command contains a the offsets and sizes of the following new
491: * symbolic information tables:
492: * table of contents
493: * module table
494: * reference symbol table
495: * indirect symbol table
496: * The first three tables above (the table of contents, module table and
497: * reference symbol table) are only present if the file is a dynamicly linked
498: * shared library. For executable and object modules, which are files
499: * containing only one module, the information that would be in these three
500: * tables is determined as follows:
501: * table of contents - the defined external symbols are sorted by name
502: * module table - the file contains only one module so everything in the
503: * file is part of the module.
504: * reference symbol table - is the defined and undefined external symbols
505: *
506: * For dynamicly linked shared library files this load command also contains
507: * offsets and sizes to the pool of relocation entries for all sections
508: * separated into two groups:
509: * external relocation entries
510: * local relocation entries
511: * For executable and object modules the relocation entries continue to hang
512: * off the section structures.
513: */
514: struct dysymtab_command {
515: unsigned long cmd; /* LC_DYSYMTAB */
516: unsigned long cmdsize; /* sizeof(struct dysymtab_command) */
517:
518: /*
519: * The symbols indicated by symoff and nsyms of the LC_SYMTAB load command
520: * are grouped into the following three groups:
521: * local symbols (further grouped by the module they are from)
522: * defined external symbols (further grouped by the module they are from)
523: * undefined symbols
524: *
525: * The local symbols are used only for debugging. The dynamic binding
526: * process may have to use them to indicate to the debugger the local
527: * symbols for a module that is being bound.
528: *
529: * The last two groups are used by the dynamic binding process to do the
530: * binding (indirectly through the module table and the reference symbol
531: * table when this is a dynamicly linked shared library file).
532: */
533: unsigned long ilocalsym; /* index to local symbols */
534: unsigned long nlocalsym; /* number of local symbols */
535:
536: unsigned long iextdefsym; /* index to externally defined symbols */
537: unsigned long nextdefsym; /* number of externally defined symbols */
538:
539: unsigned long iundefsym; /* index to undefined symbols */
540: unsigned long nundefsym; /* number of undefined symbols */
541:
542: /*
543: * For the for the dynamic binding process to find which module a symbol
544: * is defined in the table of contents is used (analogous to the ranlib
545: * structure in an archive) which maps defined external symbols to modules
546: * they are defined in. This exists only in a dynamicly linked shared
547: * library file. For executable and object modules the defined external
548: * symbols are sorted by name and is use as the table of contents.
549: */
550: unsigned long tocoff; /* file offset to table of contents */
551: unsigned long ntoc; /* number of entries in table of contents */
552:
553: /*
554: * To support dynamic binding of "modules" (whole object files) the symbol
555: * table must reflect the modules that the file was created from. This is
556: * done by having a module table that has indexes and counts into the merged
557: * tables for each module. The module structure that these two entries
558: * refer to is described below. This exists only in a dynamicly linked
559: * shared library file. For executable and object modules the file only
560: * contains one module so everything in the file belongs to the module.
561: */
562: unsigned long modtaboff; /* file offset to module table */
563: unsigned long nmodtab; /* number of module table entries */
564:
565: /*
566: * To support dynamic module binding the module structure for each module
567: * indicates the external references (defined and undefined) each module
568: * makes. For each module there is an offset and a count into the
569: * reference symbol table for the symbols that the module references.
570: * This exists only in a dynamicly linked shared library file. For
571: * executable and object modules the defined external symbols and the
572: * undefined external symbols indicates the external references.
573: */
574: unsigned long extrefsymoff; /* offset to referenced symbol table */
575: unsigned long nextrefsyms; /* number of referenced symbol table entries */
576:
577: /*
578: * The sections that contain "symbol pointers" and "routine stubs" have
579: * indexes and (implied counts based on the size of the section and fixed
580: * size of the entry) into the "indirect symbol" table for each pointer
581: * and stub. For every section of these two types the index into the
582: * indirect symbol table is stored in the section header in the field
583: * reserved1. An indirect symbol table entry is simply a 32bit index into
584: * the symbol table to the symbol that the pointer or stub is referring to.
585: * The indirect symbol table is ordered to match the entries in the section.
586: */
587: unsigned long indirectsymoff; /* file offset to the indirect symbol table */
588: unsigned long nindirectsyms; /* number of indirect symbol table entries */
589:
590: /*
591: * To support relocating an individual module in a library file quickly the
592: * external relocation entries for each module in the library need to be
593: * accessed efficiently. Since the relocation entries can't be accessed
594: * through the section headers for a library file they are separated into
595: * groups of local and external entries further grouped by module. In this
596: * case the presents of this load command who's extreloff, nextrel,
597: * locreloff and nlocrel fields are non-zero indicates that the relocation
598: * entries of non-merged sections are not referenced through the section
599: * structures (and the reloff and nreloc fields in the section headers are
600: * set to zero).
601: *
602: * Since the relocation entries are not accessed through the section headers
603: * this requires the r_address field to be something other than a section
604: * offset to identify the item to be relocated. In this case r_address is
605: * set to the offset from the vmaddr of the first LC_SEGMENT command.
606: *
607: * The relocation entries are grouped by module and the module table
608: * entries have indexes and counts into them for the group of external
609: * relocation entries for that the module.
610: *
611: * For sections that are merged across modules there must not be any
612: * remaining external relocation entries for them (for merged sections
613: * remaining relocation entries must be local).
614: */
615: unsigned long extreloff; /* offset to external relocation entries */
616: unsigned long nextrel; /* number of external relocation entries */
617:
618: /*
619: * All the local relocation entries are grouped together (they are not
620: * grouped by their module since they are only used if the object is moved
621: * from it staticly link edited address).
622: */
623: unsigned long locreloff; /* offset to local relocation entries */
624: unsigned long nlocrel; /* number of local relocation entries */
625:
626: };
627:
628: /*
629: * An indirect symbol table entry is simply a 32bit index into the symbol table
630: * to the symbol that the pointer or stub is refering to. Unless it is for a
631: * non-lazy symbol pointer section for a defined symbol which strip(1) as
632: * removed. In which case it has the value INDIRECT_SYMBOL_LOCAL. If the
633: * symbol was also absolute INDIRECT_SYMBOL_ABS is or'ed with that.
634: */
635: #define INDIRECT_SYMBOL_LOCAL 0x80000000
636: #define INDIRECT_SYMBOL_ABS 0x40000000
637:
638:
639: /* a table of contents entry */
640: struct dylib_table_of_contents {
641: unsigned long symbol_index; /* the defined external symbol
642: (index into the symbol table) */
643: unsigned long module_index; /* index into the module table this symbol
644: is defined in */
645: };
646:
647: /* a module table entry */
648: struct dylib_module {
649: unsigned long module_name; /* the module name (index into string table) */
650:
651: unsigned long iextdefsym; /* index into externally defined symbols */
652: unsigned long nextdefsym; /* number of externally defined symbols */
653: unsigned long irefsym; /* index into reference symbol table */
654: unsigned long nrefsym; /* number of reference symbol table entries */
655: unsigned long ilocalsym; /* index into symbols for local symbols */
656: unsigned long nlocalsym; /* number of local symbols */
657:
658: unsigned long iextrel; /* index into external relocation entries */
659: unsigned long nextrel; /* number of external relocation entries */
660:
661: unsigned long iinit; /* index into the init section */
662: unsigned long ninit; /* number of init section entries */
663:
664: unsigned long /* for this module address of the start of */
665: objc_module_info_addr; /* the (__OBJC,__module_info) section */
666: unsigned long /* for this module size of */
667: objc_module_info_size; /* the (__OBJC,__module_info) section */
668: };
669:
670: /*
671: * The entries in the reference symbol table are used when loading the module
672: * (both by the static and dynamic link editors) and if the module is unloaded
673: * or replaced. Therefore all external symbols (defined and undefined) are
674: * listed in the module's reference table. The flags describe the type of
675: * reference that is being made. The constants for the flags are defined in
676: * <mach-o/nlist.h> as they are also used for symbol table entries.
677: */
678: struct dylib_reference {
679: unsigned long isym:24, /* index into the symbol table */
680: flags:8; /* flags to indicate the type of reference */
681: };
682:
683: /*
684: * The symseg_command contains the offset and size of the GNU style
685: * symbol table information as described in the header file <symseg.h>.
686: * The symbol roots of the symbol segments must also be aligned properly
687: * in the file. So the requirement of keeping the offsets aligned to a
688: * multiple of a sizeof(long) translates to the length field of the symbol
689: * roots also being a multiple of a long. Also the padding must again be
690: * zeroed. (THIS IS OBSOLETE and no longer supported).
691: */
692: struct symseg_command {
693: unsigned long cmd; /* LC_SYMSEG */
694: unsigned long cmdsize; /* sizeof(struct symseg_command) */
695: unsigned long offset; /* symbol segment offset */
696: unsigned long size; /* symbol segment size in bytes */
697: };
698:
699: /*
700: * The ident_command contains a free format string table following the
701: * ident_command structure. The strings are null terminated and the size of
702: * the command is padded out with zero bytes to a multiple of sizeof(long).
703: * (THIS IS OBSOLETE and no longer supported).
704: */
705: struct ident_command {
706: unsigned long cmd; /* LC_IDENT */
707: unsigned long cmdsize; /* strings that follow this command */
708: };
709:
710: /*
711: * The fvmfile_command contains a reference to a file to be loaded at the
712: * specified virtual address. (Presently, this command is reserved for NeXT
713: * internal use. The kernel ignores this command when loading a program into
714: * memory).
715: */
716: struct fvmfile_command {
717: unsigned long cmd; /* LC_FVMFILE */
718: unsigned long cmdsize; /* includes pathname string */
719: union lc_str name; /* files pathname */
720: unsigned long header_addr; /* files virtual address */
721: };
722:
723: #endif _MACHO_LOADER_H_
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