This is a simple container format that encapsulates multiple Mach-O files, each generally for a different architecture. XNU can execute these files just like single-arch Mach-Os and will pick the appropriate entry.
This page hosts a formal specification of macOS Mach-O multiarch ("fat") binary using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for C++98/STL generated by Kaitai Struct depends on the C++/STL runtime library. You have to install it before you can parse data.
For C++, the easiest way is to clone the runtime library sources and build them along with your project.
Using Kaitai Struct in C++/STL usually consists of 3 steps.
std::istream). One can open local file for that, or use existing std::string or char* buffer.
#include <fstream>
std::ifstream is("path/to/local/file.bin", std::ifstream::binary);
#include <sstream>
std::istringstream is(str);
#include <sstream>
const char buf[] = { ... };
std::string str(buf, sizeof buf);
std::istringstream is(str);
#include "kaitai/kaitaistream.h"
kaitai::kstream ks(&is);
mach_o_fat_t data(&ks);
After that, one can get various attributes from the structure by invoking getter methods like:
data.magic() // => get magic
#ifndef MACH_O_FAT_H_
#define MACH_O_FAT_H_
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
#include "kaitai/kaitaistruct.h"
#include <stdint.h>
#include "mach_o.h"
#include <vector>
#if KAITAI_STRUCT_VERSION < 9000L
#error "Incompatible Kaitai Struct C++/STL API: version 0.9 or later is required"
#endif
class mach_o_t;
/**
* This is a simple container format that encapsulates multiple Mach-O files,
* each generally for a different architecture. XNU can execute these files just
* like single-arch Mach-Os and will pick the appropriate entry.
* \sa https://opensource.apple.com/source/xnu/xnu-7195.121.3/EXTERNAL_HEADERS/mach-o/fat.h.auto.html Source
*/
class mach_o_fat_t : public kaitai::kstruct {
public:
class fat_arch_t;
mach_o_fat_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent = 0, mach_o_fat_t* p__root = 0);
private:
void _read();
void _clean_up();
public:
~mach_o_fat_t();
class fat_arch_t : public kaitai::kstruct {
public:
fat_arch_t(kaitai::kstream* p__io, mach_o_fat_t* p__parent = 0, mach_o_fat_t* p__root = 0);
private:
void _read();
void _clean_up();
public:
~fat_arch_t();
private:
bool f_object;
mach_o_t* m_object;
public:
mach_o_t* object();
private:
mach_o_t::cpu_type_t m_cpu_type;
uint32_t m_cpu_subtype;
uint32_t m_ofs_object;
uint32_t m_len_object;
uint32_t m_align;
mach_o_fat_t* m__root;
mach_o_fat_t* m__parent;
std::string m__raw_object;
kaitai::kstream* m__io__raw_object;
public:
mach_o_t::cpu_type_t cpu_type() const { return m_cpu_type; }
uint32_t cpu_subtype() const { return m_cpu_subtype; }
uint32_t ofs_object() const { return m_ofs_object; }
uint32_t len_object() const { return m_len_object; }
uint32_t align() const { return m_align; }
mach_o_fat_t* _root() const { return m__root; }
mach_o_fat_t* _parent() const { return m__parent; }
std::string _raw_object() const { return m__raw_object; }
kaitai::kstream* _io__raw_object() const { return m__io__raw_object; }
};
private:
std::string m_magic;
uint32_t m_num_fat_arch;
std::vector<fat_arch_t*>* m_fat_archs;
mach_o_fat_t* m__root;
kaitai::kstruct* m__parent;
public:
std::string magic() const { return m_magic; }
uint32_t num_fat_arch() const { return m_num_fat_arch; }
std::vector<fat_arch_t*>* fat_archs() const { return m_fat_archs; }
mach_o_fat_t* _root() const { return m__root; }
kaitai::kstruct* _parent() const { return m__parent; }
};
#endif // MACH_O_FAT_H_
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
#include "mach_o_fat.h"
#include "kaitai/exceptions.h"
mach_o_fat_t::mach_o_fat_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent, mach_o_fat_t* p__root) : kaitai::kstruct(p__io) {
m__parent = p__parent;
m__root = this;
m_fat_archs = 0;
try {
_read();
} catch(...) {
_clean_up();
throw;
}
}
void mach_o_fat_t::_read() {
m_magic = m__io->read_bytes(4);
if (!(magic() == std::string("\xCA\xFE\xBA\xBE", 4))) {
throw kaitai::validation_not_equal_error<std::string>(std::string("\xCA\xFE\xBA\xBE", 4), magic(), _io(), std::string("/seq/0"));
}
m_num_fat_arch = m__io->read_u4be();
m_fat_archs = new std::vector<fat_arch_t*>();
const int l_fat_archs = num_fat_arch();
for (int i = 0; i < l_fat_archs; i++) {
m_fat_archs->push_back(new fat_arch_t(m__io, this, m__root));
}
}
mach_o_fat_t::~mach_o_fat_t() {
_clean_up();
}
void mach_o_fat_t::_clean_up() {
if (m_fat_archs) {
for (std::vector<fat_arch_t*>::iterator it = m_fat_archs->begin(); it != m_fat_archs->end(); ++it) {
delete *it;
}
delete m_fat_archs; m_fat_archs = 0;
}
}
mach_o_fat_t::fat_arch_t::fat_arch_t(kaitai::kstream* p__io, mach_o_fat_t* p__parent, mach_o_fat_t* p__root) : kaitai::kstruct(p__io) {
m__parent = p__parent;
m__root = p__root;
m_object = 0;
m__io__raw_object = 0;
f_object = false;
try {
_read();
} catch(...) {
_clean_up();
throw;
}
}
void mach_o_fat_t::fat_arch_t::_read() {
m_cpu_type = static_cast<mach_o_t::cpu_type_t>(m__io->read_u4be());
m_cpu_subtype = m__io->read_u4be();
m_ofs_object = m__io->read_u4be();
m_len_object = m__io->read_u4be();
m_align = m__io->read_u4be();
}
mach_o_fat_t::fat_arch_t::~fat_arch_t() {
_clean_up();
}
void mach_o_fat_t::fat_arch_t::_clean_up() {
if (f_object) {
if (m__io__raw_object) {
delete m__io__raw_object; m__io__raw_object = 0;
}
if (m_object) {
delete m_object; m_object = 0;
}
}
}
mach_o_t* mach_o_fat_t::fat_arch_t::object() {
if (f_object)
return m_object;
std::streampos _pos = m__io->pos();
m__io->seek(ofs_object());
m__raw_object = m__io->read_bytes(len_object());
m__io__raw_object = new kaitai::kstream(m__raw_object);
m_object = new mach_o_t(m__io__raw_object);
m__io->seek(_pos);
f_object = true;
return m_object;
}