dyldInitialization.cpp [plain text]
#include <stddef.h>
#include <string.h>
#include <mach/mach.h>
#include <mach-o/loader.h>
#include <mach-o/ldsyms.h>
#include <mach-o/reloc.h>
#if __ppc__ || __ppc64__
#include <mach-o/ppc/reloc.h>
#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
namespace dyldbootstrap {
typedef void (*Initializer)(int argc, const char* argv[], const char* envp[], const char* apple[]);
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);
}
}
static void rebaseDyld(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;
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);
}
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
*locationToFix += slide;
break;
}
}
}
}
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;
}
}
}
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);
}
break;
}
cmd = (const struct load_command*)(((char*)cmd)+cmd->cmdsize);
}
}
extern "C" void dyld_exceptions_init(const struct macho_header*, uintptr_t slide); extern "C" void mach_init();
uintptr_t start(const struct mach_header* appsMachHeader, int argc, const char* argv[], intptr_t slide)
{
const struct macho_header* dyldsMachHeader = (const struct macho_header*)(((char*)&_mh_dylinker_header)+slide);
if ( slide != 0 ) {
rebaseDyld(dyldsMachHeader, slide);
}
dyld_exceptions_init(dyldsMachHeader, slide);
mach_init();
segmentProtectDyld(dyldsMachHeader, slide);
const char** envp = &argv[argc+1];
const char** apple = envp;
while(*apple != NULL) { ++apple; }
++apple;
runDyldInitializers(dyldsMachHeader, slide, argc, argv, envp, apple);
return dyld::_main(appsMachHeader, argc, argv, envp, apple);
}
}