macho/macho-go/pkg/ios/fat/create-fat.go

// / Contains the declaration of FatHeader and FatArch
// / These structs are always written using Big-Endian,
// / as documented in the mach-o/fat.h
// / This file also has a CreateFat function to generate
// / Fat file from a list of MachoContext
package fat

import (
	"io"
	"os"
	"sort"

	log "github.com/sirupsen/logrus"

	. "ios-wrapper/pkg/ios"
	macho "ios-wrapper/pkg/ios/macho"
)

// / Get the alignment for the Mach-O in Fat binary
// / The returned value is the multiplier of 2
func GetAlignment(h *macho.Header) uint32 {
	switch h.Cputype() {
	case CPU_TYPE_ARM, CPU_TYPE_ARM64:
		return 0xe // log2(0x4000)
	case CPU_TYPE_POWERPC,
		CPU_TYPE_POWERPC64,
		CPU_TYPE_I386,
		CPU_TYPE_X86_64:
		return 0xc // log2(0x1000)
	default:
		return 0xd // log2(0x2000)
	}
}

func MachosToFatArchs(machos []*macho.MachoContext) []*FatArch {
	var fa []*FatArch
	for _, m := range machos {
		fa = append(fa, &FatArch{
			Cputype:    m.Header().Cputype(),
			Cpusubtype: m.Header().Cpusubtype(),
			Size:       m.FileSize(),
			Offset:     0,
			Align:      GetAlignment(m.Header()),
		})
	}
	return fa
}

// / Create a Fat binary from MachoContext
// / Convert MachoContext to FatArch
// / Calculate the alignment, now using basic calculation
// / because iOS always has valid archs ARM
// /
// / Sort the Fat arch as per the cctools/lipo
// / Calculate the offset with each Mach-O
// /
// / Write the FatHeader
// / Write the FatArchs
// / Write the Mach-Os
func CreateFat(machos []*macho.MachoContext, outfilename string) error {
	archs := MachosToFatArchs(machos)
	sort.SliceStable(archs, func(i, j int) bool {
		if archs[i].Cputype == archs[j].Cputype {
			return archs[i].Cpusubtype < archs[i].Cpusubtype
		}
		if archs[i].Cputype == CPU_TYPE_ARM64 {
			return false
		}
		if archs[j].Cputype == CPU_TYPE_ARM64 {
			return true
		}
		return archs[i].Cpusubtype < archs[j].Cpusubtype
	})

	// calculate the offset for each FatArch
	offset := uint32(8) // size of fat header, bytes
	// offset to the first macho
	offset += uint32(len(archs)) * 5 // size of fat_arch, bytes

	for _, arch := range archs {
		offset = uint32(OffsetRounder(uint64(offset), 1<<arch.Align))
		arch.Offset = offset
		offset += arch.Size

		log.WithFields(log.Fields{
			"cputype":    arch.Cputype,
			"cpusubtype": arch.Cpusubtype,
			"size":       arch.Size,
			"offset":     arch.Offset,
			"algin":      arch.Align,
		}).Debug("Arch to add")
	}

	file, err := os.OpenFile(outfilename, os.O_CREATE|os.O_WRONLY, 0777)
	if err != nil {
		return err
		// log.Fatal("Cannot open output file")
	}

	var w fatWriter
	w.WriteFatHeader(file, &FatHeader{
		Magic:     MagicFat,
		Nfat_arch: uint32(len(archs)),
	})
	w.WriteFatArchs(file, archs)
	w.WriteMachos(file, archs, machos)
	return w.err
}

type fatWriter struct {
	err error
}

func (fw *fatWriter) WriteFatHeader(w io.Writer, h *FatHeader) {
	if fw.err != nil {
		return
	}
	b := h.Serialize()
	_, err := w.Write(b)
	fw.err = err
}

func (fw *fatWriter) WriteFatArchs(w io.Writer, archs []*FatArch) {
	for _, arch := range archs {
		if fw.err != nil {
			return
		}
		b := arch.Serialize()
		_, err := w.Write(b)
		fw.err = err

		log.WithFields(log.Fields{
			"cputype":    arch.Cputype,
			"cpusubtype": arch.Cpusubtype,
			"size":       arch.Size,
			"offset":     arch.Offset,
			"algin":      arch.Align,
		}).Info("Attempt to write Fat Arch")
	}
}

// / for each fat arch sorted, we locate the MachoContext and
// / use it to Write to the buffer
// / locating the macho by its cputype and cpusubtype
func (fw *fatWriter) WriteMachos(
	w io.WriteSeeker,
	archs []*FatArch,
	machos []*macho.MachoContext,
) {
	for _, arch := range archs {
		for _, macho := range machos {
			if fw.err != nil {
				return
			}
			cputype := macho.Header().Cputype()
			cpusubtype := macho.Header().Cpusubtype()
			if cputype == arch.Cputype &&
				cpusubtype == arch.Cpusubtype {

				log.WithFields(log.Fields{
					"cputype":    cputype,
					"cpusubtype": cpusubtype,
					"offset":     arch.Offset,
					"size":       arch.Size,
				}).Info("Attempt to write Mach-O to file")

				_, err1 := w.Seek(int64(arch.Offset), io.SeekStart)
				_, err2 := macho.WriteBufferTo(w)
				if err1 != nil {
					fw.err = err1
				} else if err2 != nil {
					fw.err = err2
				}
			}
		}
	}
}

func OffsetRounder(v, r uint64) uint64 {
	r--
	v += r
	v &= uint64(^int64(r))
	return v
}