dyld-45.1.tar.gz
[apple/dyld.git] / src / dyldInitialization.cpp
1 /* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*-
2 *
3 * Copyright (c) 2004-2005 Apple Computer, Inc. All rights reserved.
4 *
5 * @APPLE_LICENSE_HEADER_START@
6 *
7 * This file contains Original Code and/or Modifications of Original Code
8 * as defined in and that are subject to the Apple Public Source License
9 * Version 2.0 (the 'License'). You may not use this file except in
10 * compliance with the License. Please obtain a copy of the License at
11 * http://www.opensource.apple.com/apsl/ and read it before using this
12 * file.
13 *
14 * The Original Code and all software distributed under the License are
15 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
16 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
17 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
19 * Please see the License for the specific language governing rights and
20 * limitations under the License.
21 *
22 * @APPLE_LICENSE_HEADER_END@
23 */
24
25 #include <stddef.h>
26 #include <string.h>
27 #include <mach/mach.h>
28 #include <mach-o/loader.h>
29 #include <mach-o/ldsyms.h>
30 #include <mach-o/reloc.h>
31 #if __ppc__ || __ppc64__
32 #include <mach-o/ppc/reloc.h>
33 #endif
34 #include "dyld.h"
35
36 #if __LP64__
37 #define macho_header mach_header_64
38 #define LC_SEGMENT_COMMAND LC_SEGMENT_64
39 #define macho_segment_command segment_command_64
40 #define macho_section section_64
41 #define RELOC_SIZE 3
42 #else
43 #define macho_header mach_header
44 #define LC_SEGMENT_COMMAND LC_SEGMENT
45 #define macho_segment_command segment_command
46 #define macho_section section
47 #define RELOC_SIZE 2
48 #endif
49
50 #define POINTER_RELOC GENERIC_RELOC_VANILLA
51
52 //
53 // Code to bootstrap dyld into a runnable state
54 //
55 //
56
57 namespace dyldbootstrap {
58
59
60 typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]);
61
62 //
63 // For a regular executable, the crt code calls dyld to run the executables initializers.
64 // For a static executable, crt directly runs the initializers.
65 // dyld (should be static) but is a dynamic executable and needs this hack to run its own initializers.
66 // We pass argc, argv, etc in case libc.a uses those arguments
67 //
68 static void runDyldInitializers(const struct macho_header* mh, intptr_t slide, int argc, const char* argv[], const char* envp[], const char* apple[])
69 {
70 const uint32_t cmd_count = mh->ncmds;
71 const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
72 const struct load_command* cmd = cmds;
73 for (uint32_t i = 0; i < cmd_count; ++i) {
74 switch (cmd->cmd) {
75 case LC_SEGMENT_COMMAND:
76 {
77 const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
78 const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
79 const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
80 for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
81 const uint8_t type = sect->flags & SECTION_TYPE;
82 if ( type == S_MOD_INIT_FUNC_POINTERS ){
83 Initializer* inits = (Initializer*)(sect->addr + slide);
84 const uint32_t count = sect->size / sizeof(uintptr_t);
85 for (uint32_t i=0; i < count; ++i) {
86 Initializer func = inits[i];
87 func(argc, argv, envp, apple);
88 }
89 }
90 }
91 }
92 break;
93 }
94 cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
95 }
96 }
97
98 //
99 // If the kernel does not load dyld at its preferred address, we need to apply
100 // fixups to various initialized parts of the __DATA segment
101 //
102 static void rebaseDyld(const struct macho_header* mh, intptr_t slide)
103 {
104 // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries)
105 // and get interesting pointers into dyld
106 const uint32_t cmd_count = mh->ncmds;
107 const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
108 const struct load_command* cmd = cmds;
109 const struct macho_segment_command* linkEditSeg = NULL;
110 const struct dysymtab_command* dynamicSymbolTable = NULL;
111 for (uint32_t i = 0; i < cmd_count; ++i) {
112 switch (cmd->cmd) {
113 case LC_SEGMENT_COMMAND:
114 {
115 const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
116 if ( strcmp(seg->segname, "__LINKEDIT") == 0 )
117 linkEditSeg = seg;
118 const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command));
119 const struct macho_section* const sectionsEnd = &sectionsStart[seg->nsects];
120 for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) {
121 const uint8_t type = sect->flags & SECTION_TYPE;
122 if ( type == S_NON_LAZY_SYMBOL_POINTERS ) {
123 // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries)
124 const uint32_t pointerCount = sect->size / sizeof(uintptr_t);
125 uintptr_t* const symbolPointers = (uintptr_t*)(sect->addr + slide);
126 for (uint32_t j=0; j < pointerCount; ++j) {
127 symbolPointers[j] += slide;
128 }
129 }
130 }
131 }
132 break;
133 case LC_DYSYMTAB:
134 dynamicSymbolTable = (struct dysymtab_command *)cmd;
135 break;
136 }
137 cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
138 }
139
140 // use reloc's to rebase all random data pointers
141 const uintptr_t relocBase = (uintptr_t)mh;
142 const relocation_info* const relocsStart = (struct relocation_info*)(linkEditSeg->vmaddr + slide + dynamicSymbolTable->locreloff - linkEditSeg->fileoff);
143 const relocation_info* const relocsEnd = &relocsStart[dynamicSymbolTable->nlocrel];
144 for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) {
145 #if __ppc__ || __ppc64__ || __i36__
146 if ( (reloc->r_address & R_SCATTERED) != 0 )
147 throw "scattered relocation in dyld";
148 #endif
149 if ( reloc->r_length != RELOC_SIZE )
150 throw "relocation in dyld has wrong size";
151
152 if ( reloc->r_type != POINTER_RELOC )
153 throw "relocation in dyld has wrong type";
154
155 // update pointer by amount dyld slid
156 *((uintptr_t*)(reloc->r_address + relocBase)) += slide;
157 }
158 }
159
160
161 //
162 // For some reason the kernel loads dyld with __TEXT and __LINKEDIT writable
163 // rdar://problem/3702311
164 //
165 static void segmentProtectDyld(const struct macho_header* mh, intptr_t slide)
166 {
167 const uint32_t cmd_count = mh->ncmds;
168 const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header));
169 const struct load_command* cmd = cmds;
170 for (uint32_t i = 0; i < cmd_count; ++i) {
171 switch (cmd->cmd) {
172 case LC_SEGMENT_COMMAND:
173 {
174 const struct macho_segment_command* seg = (struct macho_segment_command*)cmd;
175 vm_address_t addr = seg->vmaddr + slide;
176 vm_size_t size = seg->vmsize;
177 const bool setCurrentPermissions = false;
178 vm_protect(mach_task_self(), addr, size, setCurrentPermissions, seg->initprot);
179 //fprintf(stderr, "dyld: segment %s, 0x%08X -> 0x%08X, set to %d\n", seg->segname, addr, addr+size-1, seg->initprot);
180 }
181 break;
182 }
183 cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
184 }
185
186 }
187
188 extern "C" void dyld_exceptions_init(const struct macho_header*, uintptr_t slide); // in dyldExceptions.cpp
189 extern "C" void mach_init();
190
191 //
192 // This is code to bootstrap dyld. This work in normally done for a program by dyld and crt.
193 // In dyld we have to do this manually.
194 //
195 uintptr_t start(const struct mach_header* appsMachHeader, int argc, const char* argv[], intptr_t slide)
196 {
197 // _mh_dylinker_header is magic symbol defined by static linker (ld), see <mach-o/ldsyms.h>
198 const struct macho_header* dyldsMachHeader = (const struct macho_header*)(((char*)&_mh_dylinker_header)+slide);
199
200 // if kernel had to slide dyld, we need to fix up load sensitive locations
201 // we have to do this before using any global variables
202 if ( slide != 0 ) {
203 rebaseDyld(dyldsMachHeader, slide);
204 }
205
206 // enable C++ exceptions to work inside dyld
207 dyld_exceptions_init(dyldsMachHeader, slide);
208
209 // allow dyld to use mach messaging
210 mach_init();
211
212 // set protection on segments (has to be done after mach_init)
213 segmentProtectDyld(dyldsMachHeader, slide);
214
215 // kernel sets up env pointer to be just past end of agv array
216 const char** envp = &argv[argc+1];
217
218 // kernel sets up apple pointer to be just past end of envp array
219 const char** apple = envp;
220 while(*apple != NULL) { ++apple; }
221 ++apple;
222
223 // run all C++ initializers inside dyld
224 runDyldInitializers(dyldsMachHeader, slide, argc, argv, envp, apple);
225
226 // now that we are done bootstrapping dyld, call dyld's main
227 return dyld::_main(appsMachHeader, argc, argv, envp, apple);
228 }
229
230
231
232
233 } // end of namespace
234
235
236
237