| 1 | // Copyright 2018 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Except for this comment, this file is a verbatim copy of the file |
| 6 | // with the same name in $GOROOT/src/go/internal/gccgoimporter. |
| 7 | |
| 8 | package gccgoimporter |
| 9 | |
| 10 | import ( |
| 11 | "bytes" |
| 12 | "debug/elf" |
| 13 | "errors" |
| 14 | "fmt" |
| 15 | "io" |
| 16 | "strconv" |
| 17 | "strings" |
| 18 | ) |
| 19 | |
| 20 | // Magic strings for different archive file formats. |
| 21 | const ( |
| 22 | armag = "!<arch>\n" |
| 23 | armagt = "!<thin>\n" |
| 24 | armagb = "<bigaf>\n" |
| 25 | ) |
| 26 | |
| 27 | // Offsets and sizes for fields in a standard archive header. |
| 28 | const ( |
| 29 | arNameOff = 0 |
| 30 | arNameSize = 16 |
| 31 | arDateOff = arNameOff + arNameSize |
| 32 | arDateSize = 12 |
| 33 | arUIDOff = arDateOff + arDateSize |
| 34 | arUIDSize = 6 |
| 35 | arGIDOff = arUIDOff + arUIDSize |
| 36 | arGIDSize = 6 |
| 37 | arModeOff = arGIDOff + arGIDSize |
| 38 | arModeSize = 8 |
| 39 | arSizeOff = arModeOff + arModeSize |
| 40 | arSizeSize = 10 |
| 41 | arFmagOff = arSizeOff + arSizeSize |
| 42 | arFmagSize = 2 |
| 43 | |
| 44 | arHdrSize = arFmagOff + arFmagSize |
| 45 | ) |
| 46 | |
| 47 | // The contents of the fmag field of a standard archive header. |
| 48 | const arfmag = "`\n" |
| 49 | |
| 50 | // arExportData takes an archive file and returns a ReadSeeker for the |
| 51 | // export data in that file. This assumes that there is only one |
| 52 | // object in the archive containing export data, which is not quite |
| 53 | // what gccgo does; gccgo concatenates together all the export data |
| 54 | // for all the objects in the file. In practice that case does not arise. |
| 55 | func arExportData(archive io.ReadSeeker) (io.ReadSeeker, error) { |
| 56 | if _, err := archive.Seek(0, io.SeekStart); err != nil { |
| 57 | return nil, err |
| 58 | } |
| 59 | |
| 60 | var buf [len(armag)]byte |
| 61 | if _, err := archive.Read(buf[:]); err != nil { |
| 62 | return nil, err |
| 63 | } |
| 64 | |
| 65 | switch string(buf[:]) { |
| 66 | case armag: |
| 67 | return standardArExportData(archive) |
| 68 | case armagt: |
| 69 | return nil, errors.New("unsupported thin archive") |
| 70 | case armagb: |
| 71 | return nil, errors.New("unsupported AIX big archive") |
| 72 | default: |
| 73 | return nil, fmt.Errorf("unrecognized archive file format %q", buf[:]) |
| 74 | } |
| 75 | } |
| 76 | |
| 77 | // standardArExportData returns export data form a standard archive. |
| 78 | func standardArExportData(archive io.ReadSeeker) (io.ReadSeeker, error) { |
| 79 | off := int64(len(armag)) |
| 80 | for { |
| 81 | var hdrBuf [arHdrSize]byte |
| 82 | if _, err := archive.Read(hdrBuf[:]); err != nil { |
| 83 | return nil, err |
| 84 | } |
| 85 | off += arHdrSize |
| 86 | |
| 87 | if !bytes.Equal(hdrBuf[arFmagOff:arFmagOff+arFmagSize], []byte(arfmag)) { |
| 88 | return nil, fmt.Errorf("archive header format header (%q)", hdrBuf[:]) |
| 89 | } |
| 90 | |
| 91 | size, err := strconv.ParseInt(strings.TrimSpace(string(hdrBuf[arSizeOff:arSizeOff+arSizeSize])), 10, 64) |
| 92 | if err != nil { |
| 93 | return nil, fmt.Errorf("error parsing size in archive header (%q): %v", hdrBuf[:], err) |
| 94 | } |
| 95 | |
| 96 | fn := hdrBuf[arNameOff : arNameOff+arNameSize] |
| 97 | if fn[0] == '/' && (fn[1] == ' ' || fn[1] == '/' || bytes.Equal(fn[:8], []byte("/SYM64/ "))) { |
| 98 | // Archive symbol table or extended name table, |
| 99 | // which we don't care about. |
| 100 | } else { |
| 101 | archiveAt := readerAtFromSeeker(archive) |
| 102 | ret, err := elfFromAr(io.NewSectionReader(archiveAt, off, size)) |
| 103 | if ret != nil || err != nil { |
| 104 | return ret, err |
| 105 | } |
| 106 | } |
| 107 | |
| 108 | if size&1 != 0 { |
| 109 | size++ |
| 110 | } |
| 111 | off += size |
| 112 | if _, err := archive.Seek(off, io.SeekStart); err != nil { |
| 113 | return nil, err |
| 114 | } |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | // elfFromAr tries to get export data from an archive member as an ELF file. |
| 119 | // If there is no export data, this returns nil, nil. |
| 120 | func elfFromAr(member *io.SectionReader) (io.ReadSeeker, error) { |
| 121 | ef, err := elf.NewFile(member) |
| 122 | if err != nil { |
| 123 | return nil, err |
| 124 | } |
| 125 | sec := ef.Section(".go_export") |
| 126 | if sec == nil { |
| 127 | return nil, nil |
| 128 | } |
| 129 | return sec.Open(), nil |
| 130 | } |
| 131 | |
| 132 | // readerAtFromSeeker turns an io.ReadSeeker into an io.ReaderAt. |
| 133 | // This is only safe because there won't be any concurrent seeks |
| 134 | // while this code is executing. |
| 135 | func readerAtFromSeeker(rs io.ReadSeeker) io.ReaderAt { |
| 136 | if ret, ok := rs.(io.ReaderAt); ok { |
| 137 | return ret |
| 138 | } |
| 139 | return seekerReadAt{rs} |
| 140 | } |
| 141 | |
| 142 | type seekerReadAt struct { |
| 143 | seeker io.ReadSeeker |
| 144 | } |
| 145 | |
| 146 | func (sra seekerReadAt) ReadAt(p []byte, off int64) (int, error) { |
| 147 | if _, err := sra.seeker.Seek(off, io.SeekStart); err != nil { |
| 148 | return 0, err |
| 149 | } |
| 150 | return sra.seeker.Read(p) |
| 151 | } |
| 152 |
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