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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 gosym implements access to the Go symbol
// and line number tables embedded in Go binaries generated
// by the gc compilers.
package gosym

// The table format is a variant of the format used in Plan 9's a.out
// format, documented at http://plan9.bell-labs.com/magic/man2html/6/a.out.
// The best reference for the differences between the Plan 9 format
// and the Go format is the runtime source, specifically ../../runtime/symtab.c.

import (
        "encoding/binary"
        "fmt"
        "strconv"
        "strings"
)

/*
 * Symbols
 */

// A Sym represents a single symbol table entry.
type Sym struct {
        Value  uint64
        Type   byte
        Name   string
        GoType uint64
        // If this symbol if a function symbol, the corresponding Func
        Func *Func
}

// Static returns whether this symbol is static (not visible outside its file).
func (s *Sym) Static() bool { return s.Type >= 'a' }

// PackageName returns the package part of the symbol name,
// or the empty string if there is none.
func (s *Sym) PackageName() string {
        if i := strings.Index(s.Name, "."); i != -1 {
                return s.Name[0:i]
        }
        return ""
}

// ReceiverName returns the receiver type name of this symbol,
// or the empty string if there is none.
func (s *Sym) ReceiverName() string {
        l := strings.Index(s.Name, ".")
        r := strings.LastIndex(s.Name, ".")
        if l == -1 || r == -1 || l == r {
                return ""
        }
        return s.Name[l+1 : r]
}

// BaseName returns the symbol name without the package or receiver name.
func (s *Sym) BaseName() string {
        if i := strings.LastIndex(s.Name, "."); i != -1 {
                return s.Name[i+1:]
        }
        return s.Name
}

// A Func collects information about a single function.
type Func struct {
        Entry uint64
        *Sym
        End       uint64
        Params    []*Sym
        Locals    []*Sym
        FrameSize int
        LineTable *LineTable
        Obj       *Obj
}

// An Obj represents a single object file.
type Obj struct {
        Funcs []Func
        Paths []Sym
}

/*
 * Symbol tables
 */

// Table represents a Go symbol table.  It stores all of the
// symbols decoded from the program and provides methods to translate
// between symbols, names, and addresses.
type Table struct {
        Syms  []Sym
        Funcs []Func
        Files map[string]*Obj
        Objs  []Obj
        //      textEnd uint64;
}

type sym struct {
        value  uint32
        gotype uint32
        typ    byte
        name   []byte
}

func walksymtab(data []byte, fn func(sym) error) error {
        var s sym
        p := data
        for len(p) >= 6 {
                s.value = binary.BigEndian.Uint32(p[0:4])
                typ := p[4]
                if typ&0x80 == 0 {
                        return &DecodingError{len(data) - len(p) + 4, "bad symbol type", typ}
                }
                typ &^= 0x80
                s.typ = typ
                p = p[5:]
                var i int
                var nnul int
                for i = 0; i < len(p); i++ {
                        if p[i] == 0 {
                                nnul = 1
                                break
                        }
                }
                switch typ {
                case 'z', 'Z':
                        p = p[i+nnul:]
                        for i = 0; i+2 <= len(p); i += 2 {
                                if p[i] == 0 && p[i+1] == 0 {
                                        nnul = 2
                                        break
                                }
                        }
                }
                if i+nnul+4 > len(p) {
                        return &DecodingError{len(data), "unexpected EOF", nil}
                }
                s.name = p[0:i]
                i += nnul
                s.gotype = binary.BigEndian.Uint32(p[i : i+4])
                p = p[i+4:]
                fn(s)
        }
        return nil
}

// NewTable decodes the Go symbol table in data,
// returning an in-memory representation.
func NewTable(symtab []byte, pcln *LineTable) (*Table, error) {
        var n int
        err := walksymtab(symtab, func(s sym) error {
                n++
                return nil
        })
        if err != nil {
                return nil, err
        }

        var t Table
        fname := make(map[uint16]string)
        t.Syms = make([]Sym, 0, n)
        nf := 0
        nz := 0
        lasttyp := uint8(0)
        err = walksymtab(symtab, func(s sym) error {
                n := len(t.Syms)
                t.Syms = t.Syms[0 : n+1]
                ts := &t.Syms[n]
                ts.Type = s.typ
                ts.Value = uint64(s.value)
                ts.GoType = uint64(s.gotype)
                switch s.typ {
                default:
                        // rewrite name to use . instead of · (c2 b7)
                        w := 0
                        b := s.name
                        for i := 0; i < len(b); i++ {
                                if b[i] == 0xc2 && i+1 < len(b) && b[i+1] == 0xb7 {
                                        i++
                                        b[i] = '.'
                                }
                                b[w] = b[i]
                                w++
                        }
                        ts.Name = string(s.name[0:w])
                case 'z', 'Z':
                        if lasttyp != 'z' && lasttyp != 'Z' {
                                nz++
                        }
                        for i := 0; i < len(s.name); i += 2 {
                                eltIdx := binary.BigEndian.Uint16(s.name[i : i+2])
                                elt, ok := fname[eltIdx]
                                if !ok {
                                        return &DecodingError{-1, "bad filename code", eltIdx}
                                }
                                if n := len(ts.Name); n > 0 && ts.Name[n-1] != '/' {
                                        ts.Name += "/"
                                }
                                ts.Name += elt
                        }
                }
                switch s.typ {
                case 'T', 't', 'L', 'l':
                        nf++
                case 'f':
                        fname[uint16(s.value)] = ts.Name
                }
                lasttyp = s.typ
                return nil
        })
        if err != nil {
                return nil, err
        }

        t.Funcs = make([]Func, 0, nf)
        t.Objs = make([]Obj, 0, nz)
        t.Files = make(map[string]*Obj)

        // Count text symbols and attach frame sizes, parameters, and
        // locals to them.  Also, find object file boundaries.
        var obj *Obj
        lastf := 0
        for i := 0; i < len(t.Syms); i++ {
                sym := &t.Syms[i]
                switch sym.Type {
                case 'Z', 'z': // path symbol
                        // Finish the current object
                        if obj != nil {
                                obj.Funcs = t.Funcs[lastf:]
                        }
                        lastf = len(t.Funcs)

                        // Start new object
                        n := len(t.Objs)
                        t.Objs = t.Objs[0 : n+1]
                        obj = &t.Objs[n]

                        // Count & copy path symbols
                        var end int
                        for end = i + 1; end < len(t.Syms); end++ {
                                if c := t.Syms[end].Type; c != 'Z' && c != 'z' {
                                        break
                                }
                        }
                        obj.Paths = t.Syms[i:end]
                        i = end - 1 // loop will i++

                        // Record file names
                        depth := 0
                        for j := range obj.Paths {
                                s := &obj.Paths[j]
                                if s.Name == "" {
                                        depth--
                                } else {
                                        if depth == 0 {
                                                t.Files[s.Name] = obj
                                        }
                                        depth++
                                }
                        }

                case 'T', 't', 'L', 'l': // text symbol
                        if n := len(t.Funcs); n > 0 {
                                t.Funcs[n-1].End = sym.Value
                        }
                        if sym.Name == "etext" {
                                continue
                        }

                        // Count parameter and local (auto) syms
                        var np, na int
                        var end int
                countloop:
                        for end = i + 1; end < len(t.Syms); end++ {
                                switch t.Syms[end].Type {
                                case 'T', 't', 'L', 'l', 'Z', 'z':
                                        break countloop
                                case 'p':
                                        np++
                                case 'a':
                                        na++
                                }
                        }

                        // Fill in the function symbol
                        n := len(t.Funcs)
                        t.Funcs = t.Funcs[0 : n+1]
                        fn := &t.Funcs[n]
                        sym.Func = fn
                        fn.Params = make([]*Sym, 0, np)
                        fn.Locals = make([]*Sym, 0, na)
                        fn.Sym = sym
                        fn.Entry = sym.Value
                        fn.Obj = obj
                        if pcln != nil {
                                fn.LineTable = pcln.slice(fn.Entry)
                                pcln = fn.LineTable
                        }
                        for j := i; j < end; j++ {
                                s := &t.Syms[j]
                                switch s.Type {
                                case 'm':
                                        fn.FrameSize = int(s.Value)
                                case 'p':
                                        n := len(fn.Params)
                                        fn.Params = fn.Params[0 : n+1]
                                        fn.Params[n] = s
                                case 'a':
                                        n := len(fn.Locals)
                                        fn.Locals = fn.Locals[0 : n+1]
                                        fn.Locals[n] = s
                                }
                        }
                        i = end - 1 // loop will i++
                }
        }
        if obj != nil {
                obj.Funcs = t.Funcs[lastf:]
        }
        return &t, nil
}

// PCToFunc returns the function containing the program counter pc,
// or nil if there is no such function.
func (t *Table) PCToFunc(pc uint64) *Func {
        funcs := t.Funcs
        for len(funcs) > 0 {
                m := len(funcs) / 2
                fn := &funcs[m]
                switch {
                case pc < fn.Entry:
                        funcs = funcs[0:m]
                case fn.Entry <= pc && pc < fn.End:
                        return fn
                default:
                        funcs = funcs[m+1:]
                }
        }
        return nil
}

// PCToLine looks up line number information for a program counter.
// If there is no information, it returns fn == nil.
func (t *Table) PCToLine(pc uint64) (file string, line int, fn *Func) {
        if fn = t.PCToFunc(pc); fn == nil {
                return
        }
        file, line = fn.Obj.lineFromAline(fn.LineTable.PCToLine(pc))
        return
}

// LineToPC looks up the first program counter on the given line in
// the named file.  Returns UnknownPathError or UnknownLineError if
// there is an error looking up this line.
func (t *Table) LineToPC(file string, line int) (pc uint64, fn *Func, err error) {
        obj, ok := t.Files[file]
        if !ok {
                return 0, nil, UnknownFileError(file)
        }
        abs, err := obj.alineFromLine(file, line)
        if err != nil {
                return
        }
        for i := range obj.Funcs {
                f := &obj.Funcs[i]
                pc := f.LineTable.LineToPC(abs, f.End)
                if pc != 0 {
                        return pc, f, nil
                }
        }
        return 0, nil, &UnknownLineError{file, line}
}

// LookupSym returns the text, data, or bss symbol with the given name,
// or nil if no such symbol is found.
func (t *Table) LookupSym(name string) *Sym {
        // TODO(austin) Maybe make a map
        for i := range t.Syms {
                s := &t.Syms[i]
                switch s.Type {
                case 'T', 't', 'L', 'l', 'D', 'd', 'B', 'b':
                        if s.Name == name {
                                return s
                        }
                }
        }
        return nil
}

// LookupFunc returns the text, data, or bss symbol with the given name,
// or nil if no such symbol is found.
func (t *Table) LookupFunc(name string) *Func {
        for i := range t.Funcs {
                f := &t.Funcs[i]
                if f.Sym.Name == name {
                        return f
                }
        }
        return nil
}

// SymByAddr returns the text, data, or bss symbol starting at the given address.
// TODO(rsc): Allow lookup by any address within the symbol.
func (t *Table) SymByAddr(addr uint64) *Sym {
        // TODO(austin) Maybe make a map
        for i := range t.Syms {
                s := &t.Syms[i]
                switch s.Type {
                case 'T', 't', 'L', 'l', 'D', 'd', 'B', 'b':
                        if s.Value == addr {
                                return s
                        }
                }
        }
        return nil
}

/*
 * Object files
 */

func (o *Obj) lineFromAline(aline int) (string, int) {
        type stackEnt struct {
                path   string
                start  int
                offset int
                prev   *stackEnt
        }

        noPath := &stackEnt{"", 0, 0, nil}
        tos := noPath

        // TODO(austin) I have no idea how 'Z' symbols work, except
        // that they pop the stack.
pathloop:
        for _, s := range o.Paths {
                val := int(s.Value)
                switch {
                case val > aline:
                        break pathloop

                case val == 1:
                        // Start a new stack
                        tos = &stackEnt{s.Name, val, 0, noPath}

                case s.Name == "":
                        // Pop
                        if tos == noPath {
                                return "<malformed symbol table>", 0
                        }
                        tos.prev.offset += val - tos.start
                        tos = tos.prev

                default:
                        // Push
                        tos = &stackEnt{s.Name, val, 0, tos}
                }
        }

        if tos == noPath {
                return "", 0
        }
        return tos.path, aline - tos.start - tos.offset + 1
}

func (o *Obj) alineFromLine(path string, line int) (int, error) {
        if line < 1 {
                return 0, &UnknownLineError{path, line}
        }

        for i, s := range o.Paths {
                // Find this path
                if s.Name != path {
                        continue
                }

                // Find this line at this stack level
                depth := 0
                var incstart int
                line += int(s.Value)
        pathloop:
                for _, s := range o.Paths[i:] {
                        val := int(s.Value)
                        switch {
                        case depth == 1 && val >= line:
                                return line - 1, nil

                        case s.Name == "":
                                depth--
                                if depth == 0 {
                                        break pathloop
                                } else if depth == 1 {
                                        line += val - incstart
                                }

                        default:
                                if depth == 1 {
                                        incstart = val
                                }
                                depth++
                        }
                }
                return 0, &UnknownLineError{path, line}
        }
        return 0, UnknownFileError(path)
}

/*
 * Errors
 */

// UnknownFileError represents a failure to find the specific file in
// the symbol table.
type UnknownFileError string

func (e UnknownFileError) Error() string { return "unknown file: " + string(e) }

// UnknownLineError represents a failure to map a line to a program
// counter, either because the line is beyond the bounds of the file
// or because there is no code on the given line.
type UnknownLineError struct {
        File string
        Line int
}

func (e *UnknownLineError) Error() string {
        return "no code at " + e.File + ":" + strconv.Itoa(e.Line)
}

// DecodingError represents an error during the decoding of
// the symbol table.
type DecodingError struct {
        off int
        msg string
        val interface{}
}

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