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// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package macho implements access to Mach-O object files, as defined by
// http://developer.apple.com/mac/library/documentation/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html.
package macho

// High level access to low level data structures.

import (
        "bytes"
        "debug/dwarf"
        "encoding/binary"
        "errors"
        "fmt"
        "io"
        "os"
)

// A File represents an open Mach-O file.
type File struct {
        FileHeader
        ByteOrder binary.ByteOrder
        Loads     []Load
        Sections  []*Section

        Symtab   *Symtab
        Dysymtab *Dysymtab

        closer io.Closer
}

// A Load represents any Mach-O load command.
type Load interface {
        Raw() []byte
}

// A LoadBytes is the uninterpreted bytes of a Mach-O load command.
type LoadBytes []byte

func (b LoadBytes) Raw() []byte { return b }

// A SegmentHeader is the header for a Mach-O 32-bit or 64-bit load segment command.
type SegmentHeader struct {
        Cmd     LoadCmd
        Len     uint32
        Name    string
        Addr    uint64
        Memsz   uint64
        Offset  uint64
        Filesz  uint64
        Maxprot uint32
        Prot    uint32
        Nsect   uint32
        Flag    uint32
}

// A Segment represents a Mach-O 32-bit or 64-bit load segment command.
type Segment struct {
        LoadBytes
        SegmentHeader

        // Embed ReaderAt for ReadAt method.
        // Do not embed SectionReader directly
        // to avoid having Read and Seek.
        // If a client wants Read and Seek it must use
        // Open() to avoid fighting over the seek offset
        // with other clients.
        io.ReaderAt
        sr *io.SectionReader
}

// Data reads and returns the contents of the segment.
func (s *Segment) Data() ([]byte, error) {
        dat := make([]byte, s.sr.Size())
        n, err := s.sr.ReadAt(dat, 0)
        return dat[0:n], err
}

// Open returns a new ReadSeeker reading the segment.
func (s *Segment) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }

type SectionHeader struct {
        Name   string
        Seg    string
        Addr   uint64
        Size   uint64
        Offset uint32
        Align  uint32
        Reloff uint32
        Nreloc uint32
        Flags  uint32
}

type Section struct {
        SectionHeader

        // Embed ReaderAt for ReadAt method.
        // Do not embed SectionReader directly
        // to avoid having Read and Seek.
        // If a client wants Read and Seek it must use
        // Open() to avoid fighting over the seek offset
        // with other clients.
        io.ReaderAt
        sr *io.SectionReader
}

// Data reads and returns the contents of the Mach-O section.
func (s *Section) Data() ([]byte, error) {
        dat := make([]byte, s.sr.Size())
        n, err := s.sr.ReadAt(dat, 0)
        return dat[0:n], err
}

// Open returns a new ReadSeeker reading the Mach-O section.
func (s *Section) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }

// A Dylib represents a Mach-O load dynamic library command.
type Dylib struct {
        LoadBytes
        Name           string
        Time           uint32
        CurrentVersion uint32
        CompatVersion  uint32
}

// A Symtab represents a Mach-O symbol table command.
type Symtab struct {
        LoadBytes
        SymtabCmd
        Syms []Symbol
}

// A Dysymtab represents a Mach-O dynamic symbol table command.
type Dysymtab struct {
        LoadBytes
        DysymtabCmd
        IndirectSyms []uint32 // indices into Symtab.Syms
}

/*
 * Mach-O reader
 */

type FormatError struct {
        off int64
        msg string
        val interface{}
}

func (e *FormatError) Error() string {
        msg := e.msg
        if e.val != nil {
                msg += fmt.Sprintf(" '%v'", e.val)
        }
        msg += fmt.Sprintf(" in record at byte %#x", e.off)
        return msg
}

// Open opens the named file using os.Open and prepares it for use as a Mach-O binary.
func Open(name string) (*File, error) {
        f, err := os.Open(name)
        if err != nil {
                return nil, err
        }
        ff, err := NewFile(f)
        if err != nil {
                f.Close()
                return nil, err
        }
        ff.closer = f
        return ff, nil
}

// Close closes the File.
// If the File was created using NewFile directly instead of Open,
// Close has no effect.
func (f *File) Close() error {
        var err error
        if f.closer != nil {
                err = f.closer.Close()
                f.closer = nil
        }
        return err
}

// NewFile creates a new File for accessing a Mach-O binary in an underlying reader.
// The Mach-O binary is expected to start at position 0 in the ReaderAt.
func NewFile(r io.ReaderAt) (*File, error) {
        f := new(File)
        sr := io.NewSectionReader(r, 0, 1<<63-1)

        // Read and decode Mach magic to determine byte order, size.
        // Magic32 and Magic64 differ only in the bottom bit.
        var ident [4]byte
        if _, err := r.ReadAt(ident[0:], 0); err != nil {
                return nil, err
        }
        be := binary.BigEndian.Uint32(ident[0:])
        le := binary.LittleEndian.Uint32(ident[0:])
        switch Magic32 &^ 1 {
        case be &^ 1:
                f.ByteOrder = binary.BigEndian
                f.Magic = be
        case le &^ 1:
                f.ByteOrder = binary.LittleEndian
                f.Magic = le
        default:
                return nil, &FormatError{0, "invalid magic number", nil}
        }

        // Read entire file header.
        if err := binary.Read(sr, f.ByteOrder, &f.FileHeader); err != nil {
                return nil, err
        }

        // Then load commands.
        offset := int64(fileHeaderSize32)
        if f.Magic == Magic64 {
                offset = fileHeaderSize64
        }
        dat := make([]byte, f.Cmdsz)
        if _, err := r.ReadAt(dat, offset); err != nil {
                return nil, err
        }
        f.Loads = make([]Load, f.Ncmd)
        bo := f.ByteOrder
        for i := range f.Loads {
                // Each load command begins with uint32 command and length.
                if len(dat) < 8 {
                        return nil, &FormatError{offset, "command block too small", nil}
                }
                cmd, siz := LoadCmd(bo.Uint32(dat[0:4])), bo.Uint32(dat[4:8])
                if siz < 8 || siz > uint32(len(dat)) {
                        return nil, &FormatError{offset, "invalid command block size", nil}
                }
                var cmddat []byte
                cmddat, dat = dat[0:siz], dat[siz:]
                offset += int64(siz)
                var s *Segment
                switch cmd {
                default:
                        f.Loads[i] = LoadBytes(cmddat)

                case LoadCmdDylib:
                        var hdr DylibCmd
                        b := bytes.NewBuffer(cmddat)
                        if err := binary.Read(b, bo, &hdr); err != nil {
                                return nil, err
                        }
                        l := new(Dylib)
                        if hdr.Name >= uint32(len(cmddat)) {
                                return nil, &FormatError{offset, "invalid name in dynamic library command", hdr.Name}
                        }
                        l.Name = cstring(cmddat[hdr.Name:])
                        l.Time = hdr.Time
                        l.CurrentVersion = hdr.CurrentVersion
                        l.CompatVersion = hdr.CompatVersion
                        l.LoadBytes = LoadBytes(cmddat)
                        f.Loads[i] = l

                case LoadCmdSymtab:
                        var hdr SymtabCmd
                        b := bytes.NewBuffer(cmddat)
                        if err := binary.Read(b, bo, &hdr); err != nil {
                                return nil, err
                        }
                        strtab := make([]byte, hdr.Strsize)
                        if _, err := r.ReadAt(strtab, int64(hdr.Stroff)); err != nil {
                                return nil, err
                        }
                        var symsz int
                        if f.Magic == Magic64 {
                                symsz = 16
                        } else {
                                symsz = 12
                        }
                        symdat := make([]byte, int(hdr.Nsyms)*symsz)
                        if _, err := r.ReadAt(symdat, int64(hdr.Symoff)); err != nil {
                                return nil, err
                        }
                        st, err := f.parseSymtab(symdat, strtab, cmddat, &hdr, offset)
                        if err != nil {
                                return nil, err
                        }
                        f.Loads[i] = st
                        f.Symtab = st

                case LoadCmdDysymtab:
                        var hdr DysymtabCmd
                        b := bytes.NewBuffer(cmddat)
                        if err := binary.Read(b, bo, &hdr); err != nil {
                                return nil, err
                        }
                        dat := make([]byte, hdr.Nindirectsyms*4)
                        if _, err := r.ReadAt(dat, int64(hdr.Indirectsymoff)); err != nil {
                                return nil, err
                        }
                        x := make([]uint32, hdr.Nindirectsyms)
                        if err := binary.Read(bytes.NewBuffer(dat), bo, x); err != nil {
                                return nil, err
                        }
                        st := new(Dysymtab)
                        st.LoadBytes = LoadBytes(cmddat)
                        st.DysymtabCmd = hdr
                        st.IndirectSyms = x
                        f.Loads[i] = st
                        f.Dysymtab = st

                case LoadCmdSegment:
                        var seg32 Segment32
                        b := bytes.NewBuffer(cmddat)
                        if err := binary.Read(b, bo, &seg32); err != nil {
                                return nil, err
                        }
                        s = new(Segment)
                        s.LoadBytes = cmddat
                        s.Cmd = cmd
                        s.Len = siz
                        s.Name = cstring(seg32.Name[0:])
                        s.Addr = uint64(seg32.Addr)
                        s.Memsz = uint64(seg32.Memsz)
                        s.Offset = uint64(seg32.Offset)
                        s.Filesz = uint64(seg32.Filesz)
                        s.Maxprot = seg32.Maxprot
                        s.Prot = seg32.Prot
                        s.Nsect = seg32.Nsect
                        s.Flag = seg32.Flag
                        f.Loads[i] = s
                        for i := 0; i < int(s.Nsect); i++ {
                                var sh32 Section32
                                if err := binary.Read(b, bo, &sh32); err != nil {
                                        return nil, err
                                }
                                sh := new(Section)
                                sh.Name = cstring(sh32.Name[0:])
                                sh.Seg = cstring(sh32.Seg[0:])
                                sh.Addr = uint64(sh32.Addr)
                                sh.Size = uint64(sh32.Size)
                                sh.Offset = sh32.Offset
                                sh.Align = sh32.Align
                                sh.Reloff = sh32.Reloff
                                sh.Nreloc = sh32.Nreloc
                                sh.Flags = sh32.Flags
                                f.pushSection(sh, r)
                        }

                case LoadCmdSegment64:
                        var seg64 Segment64
                        b := bytes.NewBuffer(cmddat)
                        if err := binary.Read(b, bo, &seg64); err != nil {
                                return nil, err
                        }
                        s = new(Segment)
                        s.LoadBytes = cmddat
                        s.Cmd = cmd
                        s.Len = siz
                        s.Name = cstring(seg64.Name[0:])
                        s.Addr = seg64.Addr
                        s.Memsz = seg64.Memsz
                        s.Offset = seg64.Offset
                        s.Filesz = seg64.Filesz
                        s.Maxprot = seg64.Maxprot
                        s.Prot = seg64.Prot
                        s.Nsect = seg64.Nsect
                        s.Flag = seg64.Flag
                        f.Loads[i] = s
                        for i := 0; i < int(s.Nsect); i++ {
                                var sh64 Section64
                                if err := binary.Read(b, bo, &sh64); err != nil {
                                        return nil, err
                                }
                                sh := new(Section)
                                sh.Name = cstring(sh64.Name[0:])
                                sh.Seg = cstring(sh64.Seg[0:])
                                sh.Addr = sh64.Addr
                                sh.Size = sh64.Size
                                sh.Offset = sh64.Offset
                                sh.Align = sh64.Align
                                sh.Reloff = sh64.Reloff
                                sh.Nreloc = sh64.Nreloc
                                sh.Flags = sh64.Flags
                                f.pushSection(sh, r)
                        }
                }
                if s != nil {
                        s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Filesz))
                        s.ReaderAt = s.sr
                }
        }
        return f, nil
}

func (f *File) parseSymtab(symdat, strtab, cmddat []byte, hdr *SymtabCmd, offset int64) (*Symtab, error) {
        bo := f.ByteOrder
        symtab := make([]Symbol, hdr.Nsyms)
        b := bytes.NewBuffer(symdat)
        for i := range symtab {
                var n Nlist64
                if f.Magic == Magic64 {
                        if err := binary.Read(b, bo, &n); err != nil {
                                return nil, err
                        }
                } else {
                        var n32 Nlist32
                        if err := binary.Read(b, bo, &n32); err != nil {
                                return nil, err
                        }
                        n.Name = n32.Name
                        n.Type = n32.Type
                        n.Sect = n32.Sect
                        n.Desc = n32.Desc
                        n.Value = uint64(n32.Value)
                }
                sym := &symtab[i]
                if n.Name >= uint32(len(strtab)) {
                        return nil, &FormatError{offset, "invalid name in symbol table", n.Name}
                }
                sym.Name = cstring(strtab[n.Name:])
                sym.Type = n.Type
                sym.Sect = n.Sect
                sym.Desc = n.Desc
                sym.Value = n.Value
        }
        st := new(Symtab)
        st.LoadBytes = LoadBytes(cmddat)
        st.Syms = symtab
        return st, nil
}

func (f *File) pushSection(sh *Section, r io.ReaderAt) {
        f.Sections = append(f.Sections, sh)
        sh.sr = io.NewSectionReader(r, int64(sh.Offset), int64(sh.Size))
        sh.ReaderAt = sh.sr
}

func cstring(b []byte) string {
        var i int
        for i = 0; i < len(b) && b[i] != 0; i++ {
        }
        return string(b[0:i])
}

// Segment returns the first Segment with the given name, or nil if no such segment exists.
func (f *File) Segment(name string) *Segment {
        for _, l := range f.Loads {
                if s, ok := l.(*Segment); ok && s.Name == name {
                        return s
                }
        }
        return nil
}

// Section returns the first section with the given name, or nil if no such
// section exists.
func (f *File) Section(name string) *Section {
        for _, s := range f.Sections {
                if s.Name == name {
                        return s
                }
        }
        return nil
}

// DWARF returns the DWARF debug information for the Mach-O file.
func (f *File) DWARF() (*dwarf.Data, error) {
        // There are many other DWARF sections, but these
        // are the required ones, and the debug/dwarf package
        // does not use the others, so don't bother loading them.
        var names = [...]string{"abbrev", "info", "str"}
        var dat [len(names)][]byte
        for i, name := range names {
                name = "__debug_" + name
                s := f.Section(name)
                if s == nil {
                        return nil, errors.New("missing Mach-O section " + name)
                }
                b, err := s.Data()
                if err != nil && uint64(len(b)) < s.Size {
                        return nil, err
                }
                dat[i] = b
        }

        abbrev, info, str := dat[0], dat[1], dat[2]
        return dwarf.New(abbrev, nil, nil, info, nil, nil, nil, str)
}

// ImportedSymbols returns the names of all symbols
// referred to by the binary f that are expected to be
// satisfied by other libraries at dynamic load time.
func (f *File) ImportedSymbols() ([]string, error) {
        if f.Dysymtab == nil || f.Symtab == nil {
                return nil, &FormatError{0, "missing symbol table", nil}
        }

        st := f.Symtab
        dt := f.Dysymtab
        var all []string
        for _, s := range st.Syms[dt.Iundefsym : dt.Iundefsym+dt.Nundefsym] {
                all = append(all, s.Name)
        }
        return all, nil
}

// ImportedLibraries returns the paths of all libraries
// referred to by the binary f that are expected to be
// linked with the binary at dynamic link time.
func (f *File) ImportedLibraries() ([]string, error) {
        var all []string
        for _, l := range f.Loads {
                if lib, ok := l.(*Dylib); ok {
                        all = append(all, lib.Name)
                }
        }
        return all, nil
}