1 files changed, 211 insertions, 0 deletions
diff --git a/src/cmd/internal/buildid/note.go b/src/cmd/internal/buildid/note.go
new file mode 100644
index 0000000..ab98701
--- /dev/null
+++ b/src/cmd/internal/buildid/note.go
@@ -0,0 +1,211 @@
+// Copyright 2015 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 buildid
+
+import (
+	"bytes"
+	"debug/elf"
+	"debug/macho"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+)
+
+func readAligned4(r io.Reader, sz int32) ([]byte, error) {
+	full := (sz + 3) &^ 3
+	data := make([]byte, full)
+	_, err := io.ReadFull(r, data)
+	if err != nil {
+		return nil, err
+	}
+	data = data[:sz]
+	return data, nil
+}
+
+func ReadELFNote(filename, name string, typ int32) ([]byte, error) {
+	f, err := elf.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	for _, sect := range f.Sections {
+		if sect.Type != elf.SHT_NOTE {
+			continue
+		}
+		r := sect.Open()
+		for {
+			var namesize, descsize, noteType int32
+			err = binary.Read(r, f.ByteOrder, &namesize)
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				return nil, fmt.Errorf("read namesize failed: %v", err)
+			}
+			err = binary.Read(r, f.ByteOrder, &descsize)
+			if err != nil {
+				return nil, fmt.Errorf("read descsize failed: %v", err)
+			}
+			err = binary.Read(r, f.ByteOrder, &noteType)
+			if err != nil {
+				return nil, fmt.Errorf("read type failed: %v", err)
+			}
+			noteName, err := readAligned4(r, namesize)
+			if err != nil {
+				return nil, fmt.Errorf("read name failed: %v", err)
+			}
+			desc, err := readAligned4(r, descsize)
+			if err != nil {
+				return nil, fmt.Errorf("read desc failed: %v", err)
+			}
+			if name == string(noteName) && typ == noteType {
+				return desc, nil
+			}
+		}
+	}
+	return nil, nil
+}
+
+var elfGoNote = []byte("Go\x00\x00")
+var elfGNUNote = []byte("GNU\x00")
+
+// The Go build ID is stored in a note described by an ELF PT_NOTE prog
+// header. The caller has already opened filename, to get f, and read
+// at least 4 kB out, in data.
+func readELF(name string, f *os.File, data []byte) (buildid string, err error) {
+	// Assume the note content is in the data, already read.
+	// Rewrite the ELF header to set shoff and shnum to 0, so that we can pass
+	// the data to elf.NewFile and it will decode the Prog list but not
+	// try to read the section headers and the string table from disk.
+	// That's a waste of I/O when all we care about is the Prog list
+	// and the one ELF note.
+	switch elf.Class(data[elf.EI_CLASS]) {
+	case elf.ELFCLASS32:
+		data[32], data[33], data[34], data[35] = 0, 0, 0, 0
+		data[48] = 0
+		data[49] = 0
+	case elf.ELFCLASS64:
+		data[40], data[41], data[42], data[43] = 0, 0, 0, 0
+		data[44], data[45], data[46], data[47] = 0, 0, 0, 0
+		data[60] = 0
+		data[61] = 0
+	}
+
+	const elfGoBuildIDTag = 4
+	const gnuBuildIDTag = 3
+
+	ef, err := elf.NewFile(bytes.NewReader(data))
+	if err != nil {
+		return "", &fs.PathError{Path: name, Op: "parse", Err: err}
+	}
+	var gnu string
+	for _, p := range ef.Progs {
+		if p.Type != elf.PT_NOTE || p.Filesz < 16 {
+			continue
+		}
+
+		var note []byte
+		if p.Off+p.Filesz < uint64(len(data)) {
+			note = data[p.Off : p.Off+p.Filesz]
+		} else {
+			// For some linkers, such as the Solaris linker,
+			// the buildid may not be found in data (which
+			// likely contains the first 16kB of the file)
+			// or even the first few megabytes of the file
+			// due to differences in note segment placement;
+			// in that case, extract the note data manually.
+			_, err = f.Seek(int64(p.Off), io.SeekStart)
+			if err != nil {
+				return "", err
+			}
+
+			note = make([]byte, p.Filesz)
+			_, err = io.ReadFull(f, note)
+			if err != nil {
+				return "", err
+			}
+		}
+
+		filesz := p.Filesz
+		off := p.Off
+		for filesz >= 16 {
+			nameSize := ef.ByteOrder.Uint32(note)
+			valSize := ef.ByteOrder.Uint32(note[4:])
+			tag := ef.ByteOrder.Uint32(note[8:])
+			nname := note[12:16]
+			if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == elfGoBuildIDTag && bytes.Equal(nname, elfGoNote) {
+				return string(note[16 : 16+valSize]), nil
+			}
+
+			if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == gnuBuildIDTag && bytes.Equal(nname, elfGNUNote) {
+				gnu = string(note[16 : 16+valSize])
+			}
+
+			nameSize = (nameSize + 3) &^ 3
+			valSize = (valSize + 3) &^ 3
+			notesz := uint64(12 + nameSize + valSize)
+			if filesz <= notesz {
+				break
+			}
+			off += notesz
+			align := p.Align
+			alignedOff := (off + align - 1) &^ (align - 1)
+			notesz += alignedOff - off
+			off = alignedOff
+			filesz -= notesz
+			note = note[notesz:]
+		}
+	}
+
+	// If we didn't find a Go note, use a GNU note if available.
+	// This is what gccgo uses.
+	if gnu != "" {
+		return gnu, nil
+	}
+
+	// No note. Treat as successful but build ID empty.
+	return "", nil
+}
+
+// The Go build ID is stored at the beginning of the Mach-O __text segment.
+// The caller has already opened filename, to get f, and read a few kB out, in data.
+// Sadly, that's not guaranteed to hold the note, because there is an arbitrary amount
+// of other junk placed in the file ahead of the main text.
+func readMacho(name string, f *os.File, data []byte) (buildid string, err error) {
+	// If the data we want has already been read, don't worry about Mach-O parsing.
+	// This is both an optimization and a hedge against the Mach-O parsing failing
+	// in the future due to, for example, the name of the __text section changing.
+	if b, err := readRaw(name, data); b != "" && err == nil {
+		return b, err
+	}
+
+	mf, err := macho.NewFile(f)
+	if err != nil {
+		return "", &fs.PathError{Path: name, Op: "parse", Err: err}
+	}
+
+	sect := mf.Section("__text")
+	if sect == nil {
+		// Every binary has a __text section. Something is wrong.
+		return "", &fs.PathError{Path: name, Op: "parse", Err: fmt.Errorf("cannot find __text section")}
+	}
+
+	// It should be in the first few bytes, but read a lot just in case,
+	// especially given our past problems on OS X with the build ID moving.
+	// There shouldn't be much difference between reading 4kB and 32kB:
+	// the hard part is getting to the data, not transferring it.
+	n := sect.Size
+	if n > uint64(readSize) {
+		n = uint64(readSize)
+	}
+	buf := make([]byte, n)
+	if _, err := f.ReadAt(buf, int64(sect.Offset)); err != nil {
+		return "", err
+	}
+
+	return readRaw(name, buf)
+}