112 lines
2.7 KiB
Go
112 lines
2.7 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file implements FindExportData.
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package gcimporter
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import (
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"bufio"
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"errors"
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"fmt"
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"io"
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"strconv"
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"strings"
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)
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func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
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// See $GOROOT/include/ar.h.
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hdr := make([]byte, 16+12+6+6+8+10+2)
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_, err = io.ReadFull(r, hdr)
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if err != nil {
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return
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}
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// leave for debugging
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if false {
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fmt.Printf("header: %s", hdr)
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}
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s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
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size, err = strconv.Atoi(s)
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if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
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err = errors.New("invalid archive header")
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return
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}
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name = strings.TrimSpace(string(hdr[:16]))
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return
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}
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// FindExportData positions the reader r at the beginning of the
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// export data section of an underlying GC-created object/archive
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// file by reading from it. The reader must be positioned at the
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// start of the file before calling this function.
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//
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func FindExportData(r *bufio.Reader) (err error) {
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// Read first line to make sure this is an object file.
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line, err := r.ReadSlice('\n')
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if err != nil {
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return
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}
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if string(line) == "!<arch>\n" {
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// Archive file. Scan to __.PKGDEF, which should
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// be second archive entry.
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var name string
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var size int
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// First entry should be __.GOSYMDEF.
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// Older archives used __.SYMDEF, so allow that too.
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// Read and discard.
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if name, size, err = readGopackHeader(r); err != nil {
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return
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}
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if name != "__.SYMDEF" && name != "__.GOSYMDEF" {
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err = errors.New("go archive does not begin with __.SYMDEF or __.GOSYMDEF")
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return
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}
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const block = 4096
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tmp := make([]byte, block)
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for size > 0 {
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n := size
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if n > block {
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n = block
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}
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if _, err = io.ReadFull(r, tmp[:n]); err != nil {
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return
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}
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size -= n
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}
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// Second entry should be __.PKGDEF.
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if name, size, err = readGopackHeader(r); err != nil {
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return
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}
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if name != "__.PKGDEF" {
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err = errors.New("go archive is missing __.PKGDEF")
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return
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}
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// Read first line of __.PKGDEF data, so that line
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// is once again the first line of the input.
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if line, err = r.ReadSlice('\n'); err != nil {
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return
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}
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}
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// Now at __.PKGDEF in archive or still at beginning of file.
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// Either way, line should begin with "go object ".
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if !strings.HasPrefix(string(line), "go object ") {
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err = errors.New("not a go object file")
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return
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}
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// Skip over object header to export data.
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// Begins after first line with $$.
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for line[0] != '$' {
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if line, err = r.ReadSlice('\n'); err != nil {
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return
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}
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}
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return
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}
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