/* -*- mode: C++; c-basic-offset: 4; tab-width: 4 -*- * * Copyright (c) 2004-2005 Apple Computer, Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ #include #include #include #include #include #include #if __ppc__ || __ppc64__ #include #endif #include "dyld.h" #if __LP64__ #define macho_header mach_header_64 #define LC_SEGMENT_COMMAND LC_SEGMENT_64 #define macho_segment_command segment_command_64 #define macho_section section_64 #define RELOC_SIZE 3 #else #define macho_header mach_header #define LC_SEGMENT_COMMAND LC_SEGMENT #define macho_segment_command segment_command #define macho_section section #define RELOC_SIZE 2 #endif // // Code to bootstrap dyld into a runnable state // // namespace dyldbootstrap { typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]); // // For a regular executable, the crt code calls dyld to run the executables initializers. // For a static executable, crt directly runs the initializers. // dyld (should be static) but is a dynamic executable and needs this hack to run its own initializers. // We pass argc, argv, etc in case libc.a uses those arguments // static void runDyldInitializers(const struct macho_header* mh, intptr_t slide, int argc, const char* argv[], const char* envp[], const char* apple[]) { const uint32_t cmd_count = mh->ncmds; const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header)); const struct load_command* cmd = cmds; for (uint32_t i = 0; i < cmd_count; ++i) { switch (cmd->cmd) { case LC_SEGMENT_COMMAND: { const struct macho_segment_command* seg = (struct macho_segment_command*)cmd; const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command)); const struct macho_section* const sectionsEnd = §ionsStart[seg->nsects]; for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) { const uint8_t type = sect->flags & SECTION_TYPE; if ( type == S_MOD_INIT_FUNC_POINTERS ){ Initializer* inits = (Initializer*)(sect->addr + slide); const uint32_t count = sect->size / sizeof(uintptr_t); for (uint32_t i=0; i < count; ++i) { Initializer func = inits[i]; func(argc, argv, envp, apple); } } } } break; } cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize); } } // // If the kernel does not load dyld at its preferred address, we need to apply // fixups to various initialized parts of the __DATA segment // static void rebaseDyld(const struct macho_header* mh, intptr_t slide) { // get interesting pointers into dyld const uint32_t cmd_count = mh->ncmds; const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header)); const struct load_command* cmd = cmds; const struct macho_segment_command* linkEditSeg = NULL; const struct dysymtab_command* dynamicSymbolTable = NULL; const struct macho_section* nonLazySection = NULL; for (uint32_t i = 0; i < cmd_count; ++i) { switch (cmd->cmd) { case LC_SEGMENT_COMMAND: { const struct macho_segment_command* seg = (struct macho_segment_command*)cmd; if ( strcmp(seg->segname, "__LINKEDIT") == 0 ) linkEditSeg = seg; const struct macho_section* const sectionsStart = (struct macho_section*)((char*)seg + sizeof(struct macho_segment_command)); const struct macho_section* const sectionsEnd = §ionsStart[seg->nsects]; for (const struct macho_section* sect=sectionsStart; sect < sectionsEnd; ++sect) { const uint8_t type = sect->flags & SECTION_TYPE; if ( type == S_NON_LAZY_SYMBOL_POINTERS ) nonLazySection = sect; } } break; case LC_DYSYMTAB: dynamicSymbolTable = (struct dysymtab_command *)cmd; break; } cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize); } // use reloc's to rebase all random data pointers const uintptr_t relocBase = (uintptr_t)mh; const relocation_info* const relocsStart = (struct relocation_info*)(linkEditSeg->vmaddr + slide + dynamicSymbolTable->locreloff - linkEditSeg->fileoff); const relocation_info* const relocsEnd = &relocsStart[dynamicSymbolTable->nlocrel]; for (const relocation_info* reloc=relocsStart; reloc < relocsEnd; ++reloc) { if ( (reloc->r_address & R_SCATTERED) == 0 ) { if (reloc->r_length == RELOC_SIZE) { switch(reloc->r_type) { case GENERIC_RELOC_VANILLA: *((uintptr_t*)(reloc->r_address + relocBase)) += slide; break; } } } else { const struct scattered_relocation_info* sreloc = (struct scattered_relocation_info*)reloc; if (sreloc->r_length == RELOC_SIZE) { uintptr_t* locationToFix = (uintptr_t*)(sreloc->r_address + relocBase); switch(sreloc->r_type) { case GENERIC_RELOC_VANILLA: #if __ppc__ || __ppc64__ case PPC_RELOC_PB_LA_PTR: #elif __i386__ case GENERIC_RELOC_PB_LA_PTR: #endif // Note the use of PB_LA_PTR is unique here. Seems like ld should strip out all lazy pointers // but it does not. But, since all lazy-pointers point within dyld, they can be slid too *locationToFix += slide; break; } } } } // rebase non-lazy pointers (which all point internal to dyld, since dyld uses no shared libraries) if ( nonLazySection != NULL ) { const uint32_t pointerCount = nonLazySection->size / sizeof(uintptr_t); uintptr_t* const symbolPointers = (uintptr_t*)(nonLazySection->addr + slide); for (uint32_t j=0; j < pointerCount; ++j) { symbolPointers[j] += slide; } } } // // For some reason the kernel loads dyld with __TEXT and __LINKEDIT writable // rdar://problem/3702311 // static void segmentProtectDyld(const struct macho_header* mh, intptr_t slide) { const uint32_t cmd_count = mh->ncmds; const struct load_command* const cmds = (struct load_command*)(((char*)mh)+sizeof(macho_header)); const struct load_command* cmd = cmds; for (uint32_t i = 0; i < cmd_count; ++i) { switch (cmd->cmd) { case LC_SEGMENT_COMMAND: { const struct macho_segment_command* seg = (struct macho_segment_command*)cmd; vm_address_t addr = seg->vmaddr + slide; vm_size_t size = seg->vmsize; const bool setCurrentPermissions = false; vm_protect(mach_task_self(), addr, size, setCurrentPermissions, seg->initprot); //fprintf(stderr, "dyld: segment %s, 0x%08X -> 0x%08X, set to %d\n", seg->segname, addr, addr+size-1, seg->initprot); } break; } cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize); } } extern "C" void dyld_exceptions_init(const struct macho_header*, uintptr_t slide); // in dyldExceptions.cpp extern "C" void mach_init(); // // This is code to bootstrap dyld. This work in normally done for a program by dyld and crt. // In dyld we have to do this manually. // uintptr_t start(const struct mach_header* appsMachHeader, int argc, const char* argv[], intptr_t slide) { // _mh_dylinker_header is magic symbol defined by static linker (ld), see const struct macho_header* dyldsMachHeader = (const struct macho_header*)(((char*)&_mh_dylinker_header)+slide); // if kernel had to slide dyld, we need to fix up load sensitive locations // we have to do this before using any global variables if ( slide != 0 ) { rebaseDyld(dyldsMachHeader, slide); } // enable C++ exceptions to work inside dyld dyld_exceptions_init(dyldsMachHeader, slide); // allow dyld to use mach messaging mach_init(); // set protection on segments (has to be done after mach_init) segmentProtectDyld(dyldsMachHeader, slide); // kernel sets up env pointer to be just past end of agv array const char** envp = &argv[argc+1]; // kernel sets up apple pointer to be just past end of envp array const char** apple = envp; while(*apple != NULL) { ++apple; } ++apple; // run all C++ initializers inside dyld runDyldInitializers(dyldsMachHeader, slide, argc, argv, envp, apple); // now that we are done bootstrapping dyld, call dyld's main return dyld::_main(appsMachHeader, argc, argv, envp, apple); } } // end of namespace