LWG 3035. std::allocator's constructors should be constexpr

[official-gcc.git] / libgo / go / debug / gosym / pclntab.go

// 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.

/*
 * Line tables
 */

package gosym

import (
        "encoding/binary"
        "sync"
)

// A LineTable is a data structure mapping program counters to line numbers.
//
// In Go 1.1 and earlier, each function (represented by a Func) had its own LineTable,
// and the line number corresponded to a numbering of all source lines in the
// program, across all files. That absolute line number would then have to be
// converted separately to a file name and line number within the file.
//
// In Go 1.2, the format of the data changed so that there is a single LineTable
// for the entire program, shared by all Funcs, and there are no absolute line
// numbers, just line numbers within specific files.
//
// For the most part, LineTable's methods should be treated as an internal
// detail of the package; callers should use the methods on Table instead.
type LineTable struct {
        Data []byte
        PC   uint64
        Line int

        // Go 1.2 state
        mu       sync.Mutex
        go12     int // is this in Go 1.2 format? -1 no, 0 unknown, 1 yes
        binary   binary.ByteOrder
        quantum  uint32
        ptrsize  uint32
        functab  []byte
        nfunctab uint32
        filetab  []byte
        nfiletab uint32
        fileMap  map[string]uint32
}

// NOTE(rsc): This is wrong for GOARCH=arm, which uses a quantum of 4,
// but we have no idea whether we're using arm or not. This only
// matters in the old (pre-Go 1.2) symbol table format, so it's not worth
// fixing.
const oldQuantum = 1

func (t *LineTable) parse(targetPC uint64, targetLine int) (b []byte, pc uint64, line int) {
        // The PC/line table can be thought of as a sequence of
        //  <pc update>* <line update>
        // batches. Each update batch results in a (pc, line) pair,
        // where line applies to every PC from pc up to but not
        // including the pc of the next pair.
        //
        // Here we process each update individually, which simplifies
        // the code, but makes the corner cases more confusing.
        b, pc, line = t.Data, t.PC, t.Line
        for pc <= targetPC && line != targetLine && len(b) > 0 {
                code := b[0]
                b = b[1:]
                switch {
                case code == 0:
                        if len(b) < 4 {
                                b = b[0:0]
                                break
                        }
                        val := binary.BigEndian.Uint32(b)
                        b = b[4:]
                        line += int(val)
                case code <= 64:
                        line += int(code)
                case code <= 128:
                        line -= int(code - 64)
                default:
                        pc += oldQuantum * uint64(code-128)
                        continue
                }
                pc += oldQuantum
        }
        return b, pc, line
}

func (t *LineTable) slice(pc uint64) *LineTable {
        data, pc, line := t.parse(pc, -1)
        return &LineTable{Data: data, PC: pc, Line: line}
}

// PCToLine returns the line number for the given program counter.
// Callers should use Table's PCToLine method instead.
func (t *LineTable) PCToLine(pc uint64) int {
        if t.isGo12() {
                return t.go12PCToLine(pc)
        }
        _, _, line := t.parse(pc, -1)
        return line
}

// LineToPC returns the program counter for the given line number,
// considering only program counters before maxpc.
// Callers should use Table's LineToPC method instead.
func (t *LineTable) LineToPC(line int, maxpc uint64) uint64 {
        if t.isGo12() {
                return 0
        }
        _, pc, line1 := t.parse(maxpc, line)
        if line1 != line {
                return 0
        }
        // Subtract quantum from PC to account for post-line increment
        return pc - oldQuantum
}

// NewLineTable returns a new PC/line table
// corresponding to the encoded data.
// Text must be the start address of the
// corresponding text segment.
func NewLineTable(data []byte, text uint64) *LineTable {
        return &LineTable{Data: data, PC: text, Line: 0}
}

// Go 1.2 symbol table format.
// See golang.org/s/go12symtab.
//
// A general note about the methods here: rather than try to avoid
// index out of bounds errors, we trust Go to detect them, and then
// we recover from the panics and treat them as indicative of a malformed
// or incomplete table.
//
// The methods called by symtab.go, which begin with "go12" prefixes,
// are expected to have that recovery logic.

// isGo12 reports whether this is a Go 1.2 (or later) symbol table.
func (t *LineTable) isGo12() bool {
        t.go12Init()
        return t.go12 == 1
}

const go12magic = 0xfffffffb

// uintptr returns the pointer-sized value encoded at b.
// The pointer size is dictated by the table being read.
func (t *LineTable) uintptr(b []byte) uint64 {
        if t.ptrsize == 4 {
                return uint64(t.binary.Uint32(b))
        }
        return t.binary.Uint64(b)
}

// go12init initializes the Go 1.2 metadata if t is a Go 1.2 symbol table.
func (t *LineTable) go12Init() {
        t.mu.Lock()
        defer t.mu.Unlock()
        if t.go12 != 0 {
                return
        }

        defer func() {
                // If we panic parsing, assume it's not a Go 1.2 symbol table.
                recover()
        }()

        // Check header: 4-byte magic, two zeros, pc quantum, pointer size.
        t.go12 = -1 // not Go 1.2 until proven otherwise
        if len(t.Data) < 16 || t.Data[4] != 0 || t.Data[5] != 0 ||
                (t.Data[6] != 1 && t.Data[6] != 2 && t.Data[6] != 4) || // pc quantum
                (t.Data[7] != 4 && t.Data[7] != 8) { // pointer size
                return
        }

        switch uint32(go12magic) {
        case binary.LittleEndian.Uint32(t.Data):
                t.binary = binary.LittleEndian
        case binary.BigEndian.Uint32(t.Data):
                t.binary = binary.BigEndian
        default:
                return
        }

        t.quantum = uint32(t.Data[6])
        t.ptrsize = uint32(t.Data[7])

        t.nfunctab = uint32(t.uintptr(t.Data[8:]))
        t.functab = t.Data[8+t.ptrsize:]
        functabsize := t.nfunctab*2*t.ptrsize + t.ptrsize
        fileoff := t.binary.Uint32(t.functab[functabsize:])
        t.functab = t.functab[:functabsize]
        t.filetab = t.Data[fileoff:]
        t.nfiletab = t.binary.Uint32(t.filetab)
        t.filetab = t.filetab[:t.nfiletab*4]

        t.go12 = 1 // so far so good
}

// go12Funcs returns a slice of Funcs derived from the Go 1.2 pcln table.
func (t *LineTable) go12Funcs() []Func {
        // Assume it is malformed and return nil on error.
        defer func() {
                recover()
        }()

        n := len(t.functab) / int(t.ptrsize) / 2
        funcs := make([]Func, n)
        for i := range funcs {
                f := &funcs[i]
                f.Entry = t.uintptr(t.functab[2*i*int(t.ptrsize):])
                f.End = t.uintptr(t.functab[(2*i+2)*int(t.ptrsize):])
                info := t.Data[t.uintptr(t.functab[(2*i+1)*int(t.ptrsize):]):]
                f.LineTable = t
                f.FrameSize = int(t.binary.Uint32(info[t.ptrsize+2*4:]))
                f.Sym = &Sym{
                        Value:  f.Entry,
                        Type:   'T',
                        Name:   t.string(t.binary.Uint32(info[t.ptrsize:])),
                        GoType: 0,
                        Func:   f,
                }
        }
        return funcs
}

// findFunc returns the func corresponding to the given program counter.
func (t *LineTable) findFunc(pc uint64) []byte {
        if pc < t.uintptr(t.functab) || pc >= t.uintptr(t.functab[len(t.functab)-int(t.ptrsize):]) {
                return nil
        }

        // The function table is a list of 2*nfunctab+1 uintptrs,
        // alternating program counters and offsets to func structures.
        f := t.functab
        nf := t.nfunctab
        for nf > 0 {
                m := nf / 2
                fm := f[2*t.ptrsize*m:]
                if t.uintptr(fm) <= pc && pc < t.uintptr(fm[2*t.ptrsize:]) {
                        return t.Data[t.uintptr(fm[t.ptrsize:]):]
                } else if pc < t.uintptr(fm) {
                        nf = m
                } else {
                        f = f[(m+1)*2*t.ptrsize:]
                        nf -= m + 1
                }
        }
        return nil
}

// readvarint reads, removes, and returns a varint from *pp.
func (t *LineTable) readvarint(pp *[]byte) uint32 {
        var v, shift uint32
        p := *pp
        for shift = 0; ; shift += 7 {
                b := p[0]
                p = p[1:]
                v |= (uint32(b) & 0x7F) << shift
                if b&0x80 == 0 {
                        break
                }
        }
        *pp = p
        return v
}

// string returns a Go string found at off.
func (t *LineTable) string(off uint32) string {
        for i := off; ; i++ {
                if t.Data[i] == 0 {
                        return string(t.Data[off:i])
                }
        }
}

// step advances to the next pc, value pair in the encoded table.
func (t *LineTable) step(p *[]byte, pc *uint64, val *int32, first bool) bool {
        uvdelta := t.readvarint(p)
        if uvdelta == 0 && !first {
                return false
        }
        if uvdelta&1 != 0 {
                uvdelta = ^(uvdelta >> 1)
        } else {
                uvdelta >>= 1
        }
        vdelta := int32(uvdelta)
        pcdelta := t.readvarint(p) * t.quantum
        *pc += uint64(pcdelta)
        *val += vdelta
        return true
}

// pcvalue reports the value associated with the target pc.
// off is the offset to the beginning of the pc-value table,
// and entry is the start PC for the corresponding function.
func (t *LineTable) pcvalue(off uint32, entry, targetpc uint64) int32 {
        p := t.Data[off:]

        val := int32(-1)
        pc := entry
        for t.step(&p, &pc, &val, pc == entry) {
                if targetpc < pc {
                        return val
                }
        }
        return -1
}

// findFileLine scans one function in the binary looking for a
// program counter in the given file on the given line.
// It does so by running the pc-value tables mapping program counter
// to file number. Since most functions come from a single file, these
// are usually short and quick to scan. If a file match is found, then the
// code goes to the expense of looking for a simultaneous line number match.
func (t *LineTable) findFileLine(entry uint64, filetab, linetab uint32, filenum, line int32) uint64 {
        if filetab == 0 || linetab == 0 {
                return 0
        }

        fp := t.Data[filetab:]
        fl := t.Data[linetab:]
        fileVal := int32(-1)
        filePC := entry
        lineVal := int32(-1)
        linePC := entry
        fileStartPC := filePC
        for t.step(&fp, &filePC, &fileVal, filePC == entry) {
                if fileVal == filenum && fileStartPC < filePC {
                        // fileVal is in effect starting at fileStartPC up to
                        // but not including filePC, and it's the file we want.
                        // Run the PC table looking for a matching line number
                        // or until we reach filePC.
                        lineStartPC := linePC
                        for linePC < filePC && t.step(&fl, &linePC, &lineVal, linePC == entry) {
                                // lineVal is in effect until linePC, and lineStartPC < filePC.
                                if lineVal == line {
                                        if fileStartPC <= lineStartPC {
                                                return lineStartPC
                                        }
                                        if fileStartPC < linePC {
                                                return fileStartPC
                                        }
                                }
                                lineStartPC = linePC
                        }
                }
                fileStartPC = filePC
        }
        return 0
}

// go12PCToLine maps program counter to line number for the Go 1.2 pcln table.
func (t *LineTable) go12PCToLine(pc uint64) (line int) {
        defer func() {
                if recover() != nil {
                        line = -1
                }
        }()

        f := t.findFunc(pc)
        if f == nil {
                return -1
        }
        entry := t.uintptr(f)
        linetab := t.binary.Uint32(f[t.ptrsize+5*4:])
        return int(t.pcvalue(linetab, entry, pc))
}

// go12PCToFile maps program counter to file name for the Go 1.2 pcln table.
func (t *LineTable) go12PCToFile(pc uint64) (file string) {
        defer func() {
                if recover() != nil {
                        file = ""
                }
        }()

        f := t.findFunc(pc)
        if f == nil {
                return ""
        }
        entry := t.uintptr(f)
        filetab := t.binary.Uint32(f[t.ptrsize+4*4:])
        fno := t.pcvalue(filetab, entry, pc)
        if fno <= 0 {
                return ""
        }
        return t.string(t.binary.Uint32(t.filetab[4*fno:]))
}

// go12LineToPC maps a (file, line) pair to a program counter for the Go 1.2 pcln table.
func (t *LineTable) go12LineToPC(file string, line int) (pc uint64) {
        defer func() {
                if recover() != nil {
                        pc = 0
                }
        }()

        t.initFileMap()
        filenum := t.fileMap[file]
        if filenum == 0 {
                return 0
        }

        // Scan all functions.
        // If this turns out to be a bottleneck, we could build a map[int32][]int32
        // mapping file number to a list of functions with code from that file.
        for i := uint32(0); i < t.nfunctab; i++ {
                f := t.Data[t.uintptr(t.functab[2*t.ptrsize*i+t.ptrsize:]):]
                entry := t.uintptr(f)
                filetab := t.binary.Uint32(f[t.ptrsize+4*4:])
                linetab := t.binary.Uint32(f[t.ptrsize+5*4:])
                pc := t.findFileLine(entry, filetab, linetab, int32(filenum), int32(line))
                if pc != 0 {
                        return pc
                }
        }
        return 0
}

// initFileMap initializes the map from file name to file number.
func (t *LineTable) initFileMap() {
        t.mu.Lock()
        defer t.mu.Unlock()

        if t.fileMap != nil {
                return
        }
        m := make(map[string]uint32)

        for i := uint32(1); i < t.nfiletab; i++ {
                s := t.string(t.binary.Uint32(t.filetab[4*i:]))
                m[s] = i
        }
        t.fileMap = m
}

// go12MapFiles adds to m a key for every file in the Go 1.2 LineTable.
// Every key maps to obj. That's not a very interesting map, but it provides
// a way for callers to obtain the list of files in the program.
func (t *LineTable) go12MapFiles(m map[string]*Obj, obj *Obj) {
        defer func() {
                recover()
        }()

        t.initFileMap()
        for file := range t.fileMap {
                m[file] = obj
        }
}