1 files changed, 400 insertions, 0 deletions
diff --git a/src/debug/buildinfo/buildinfo.go b/src/debug/buildinfo/buildinfo.go
new file mode 100644
index 0000000..d1f4892
--- /dev/null
+++ b/src/debug/buildinfo/buildinfo.go
@@ -0,0 +1,400 @@
+// Copyright 2021 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 buildinfo provides access to information embedded in a Go binary
+// about how it was built. This includes the Go toolchain version, and the
+// set of modules used (for binaries built in module mode).
+//
+// Build information is available for the currently running binary in
+// runtime/debug.ReadBuildInfo.
+package buildinfo
+
+import (
+	"bytes"
+	"debug/elf"
+	"debug/macho"
+	"debug/pe"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"internal/xcoff"
+	"io"
+	"io/fs"
+	"os"
+	"runtime/debug"
+)
+
+// Type alias for build info. We cannot move the types here, since
+// runtime/debug would need to import this package, which would make it
+// a much larger dependency.
+type BuildInfo = debug.BuildInfo
+
+var (
+	// errUnrecognizedFormat is returned when a given executable file doesn't
+	// appear to be in a known format, or it breaks the rules of that format,
+	// or when there are I/O errors reading the file.
+	errUnrecognizedFormat = errors.New("unrecognized file format")
+
+	// errNotGoExe is returned when a given executable file is valid but does
+	// not contain Go build information.
+	errNotGoExe = errors.New("not a Go executable")
+
+	// The build info blob left by the linker is identified by
+	// a 16-byte header, consisting of buildInfoMagic (14 bytes),
+	// the binary's pointer size (1 byte),
+	// and whether the binary is big endian (1 byte).
+	buildInfoMagic = []byte("\xff Go buildinf:")
+)
+
+// ReadFile returns build information embedded in a Go binary
+// file at the given path. Most information is only available for binaries built
+// with module support.
+func ReadFile(name string) (info *BuildInfo, err error) {
+	defer func() {
+		if pathErr := (*fs.PathError)(nil); errors.As(err, &pathErr) {
+			err = fmt.Errorf("could not read Go build info: %w", err)
+		} else if err != nil {
+			err = fmt.Errorf("could not read Go build info from %s: %w", name, err)
+		}
+	}()
+
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return Read(f)
+}
+
+// Read returns build information embedded in a Go binary file
+// accessed through the given ReaderAt. Most information is only available for
+// binaries built with module support.
+func Read(r io.ReaderAt) (*BuildInfo, error) {
+	vers, mod, err := readRawBuildInfo(r)
+	if err != nil {
+		return nil, err
+	}
+	bi, err := debug.ParseBuildInfo(mod)
+	if err != nil {
+		return nil, err
+	}
+	bi.GoVersion = vers
+	return bi, nil
+}
+
+type exe interface {
+	// ReadData reads and returns up to size bytes starting at virtual address addr.
+	ReadData(addr, size uint64) ([]byte, error)
+
+	// DataStart returns the virtual address of the segment or section that
+	// should contain build information. This is either a specially named section
+	// or the first writable non-zero data segment.
+	DataStart() uint64
+}
+
+// readRawBuildInfo extracts the Go toolchain version and module information
+// strings from a Go binary. On success, vers should be non-empty. mod
+// is empty if the binary was not built with modules enabled.
+func readRawBuildInfo(r io.ReaderAt) (vers, mod string, err error) {
+	// Read the first bytes of the file to identify the format, then delegate to
+	// a format-specific function to load segment and section headers.
+	ident := make([]byte, 16)
+	if n, err := r.ReadAt(ident, 0); n < len(ident) || err != nil {
+		return "", "", errUnrecognizedFormat
+	}
+
+	var x exe
+	switch {
+	case bytes.HasPrefix(ident, []byte("\x7FELF")):
+		f, err := elf.NewFile(r)
+		if err != nil {
+			return "", "", errUnrecognizedFormat
+		}
+		x = &elfExe{f}
+	case bytes.HasPrefix(ident, []byte("MZ")):
+		f, err := pe.NewFile(r)
+		if err != nil {
+			return "", "", errUnrecognizedFormat
+		}
+		x = &peExe{f}
+	case bytes.HasPrefix(ident, []byte("\xFE\xED\xFA")) || bytes.HasPrefix(ident[1:], []byte("\xFA\xED\xFE")):
+		f, err := macho.NewFile(r)
+		if err != nil {
+			return "", "", errUnrecognizedFormat
+		}
+		x = &machoExe{f}
+	case bytes.HasPrefix(ident, []byte{0x01, 0xDF}) || bytes.HasPrefix(ident, []byte{0x01, 0xF7}):
+		f, err := xcoff.NewFile(r)
+		if err != nil {
+			return "", "", errUnrecognizedFormat
+		}
+		x = &xcoffExe{f}
+	default:
+		return "", "", errUnrecognizedFormat
+	}
+
+	// Read the first 64kB of dataAddr to find the build info blob.
+	// On some platforms, the blob will be in its own section, and DataStart
+	// returns the address of that section. On others, it's somewhere in the
+	// data segment; the linker puts it near the beginning.
+	// See cmd/link/internal/ld.Link.buildinfo.
+	dataAddr := x.DataStart()
+	data, err := x.ReadData(dataAddr, 64*1024)
+	if err != nil {
+		return "", "", err
+	}
+	const (
+		buildInfoAlign = 16
+		buildInfoSize  = 32
+	)
+	for {
+		i := bytes.Index(data, buildInfoMagic)
+		if i < 0 || len(data)-i < buildInfoSize {
+			return "", "", errNotGoExe
+		}
+		if i%buildInfoAlign == 0 && len(data)-i >= buildInfoSize {
+			data = data[i:]
+			break
+		}
+		data = data[(i+buildInfoAlign-1)&^buildInfoAlign:]
+	}
+
+	// Decode the blob.
+	// The first 14 bytes are buildInfoMagic.
+	// The next two bytes indicate pointer size in bytes (4 or 8) and endianness
+	// (0 for little, 1 for big).
+	// Two virtual addresses to Go strings follow that: runtime.buildVersion,
+	// and runtime.modinfo.
+	// On 32-bit platforms, the last 8 bytes are unused.
+	// If the endianness has the 2 bit set, then the pointers are zero
+	// and the 32-byte header is followed by varint-prefixed string data
+	// for the two string values we care about.
+	ptrSize := int(data[14])
+	if data[15]&2 != 0 {
+		vers, data = decodeString(data[32:])
+		mod, data = decodeString(data)
+	} else {
+		bigEndian := data[15] != 0
+		var bo binary.ByteOrder
+		if bigEndian {
+			bo = binary.BigEndian
+		} else {
+			bo = binary.LittleEndian
+		}
+		var readPtr func([]byte) uint64
+		if ptrSize == 4 {
+			readPtr = func(b []byte) uint64 { return uint64(bo.Uint32(b)) }
+		} else {
+			readPtr = bo.Uint64
+		}
+		vers = readString(x, ptrSize, readPtr, readPtr(data[16:]))
+		mod = readString(x, ptrSize, readPtr, readPtr(data[16+ptrSize:]))
+	}
+	if vers == "" {
+		return "", "", errNotGoExe
+	}
+	if len(mod) >= 33 && mod[len(mod)-17] == '\n' {
+		// Strip module framing: sentinel strings delimiting the module info.
+		// These are cmd/go/internal/modload.infoStart and infoEnd.
+		mod = mod[16 : len(mod)-16]
+	} else {
+		mod = ""
+	}
+
+	return vers, mod, nil
+}
+
+func decodeString(data []byte) (s string, rest []byte) {
+	u, n := binary.Uvarint(data)
+	if n <= 0 || u >= uint64(len(data)-n) {
+		return "", nil
+	}
+	return string(data[n : uint64(n)+u]), data[uint64(n)+u:]
+}
+
+// readString returns the string at address addr in the executable x.
+func readString(x exe, ptrSize int, readPtr func([]byte) uint64, addr uint64) string {
+	hdr, err := x.ReadData(addr, uint64(2*ptrSize))
+	if err != nil || len(hdr) < 2*ptrSize {
+		return ""
+	}
+	dataAddr := readPtr(hdr)
+	dataLen := readPtr(hdr[ptrSize:])
+	data, err := x.ReadData(dataAddr, dataLen)
+	if err != nil || uint64(len(data)) < dataLen {
+		return ""
+	}
+	return string(data)
+}
+
+// elfExe is the ELF implementation of the exe interface.
+type elfExe struct {
+	f *elf.File
+}
+
+func (x *elfExe) ReadData(addr, size uint64) ([]byte, error) {
+	for _, prog := range x.f.Progs {
+		if prog.Vaddr <= addr && addr <= prog.Vaddr+prog.Filesz-1 {
+			n := prog.Vaddr + prog.Filesz - addr
+			if n > size {
+				n = size
+			}
+			data := make([]byte, n)
+			_, err := prog.ReadAt(data, int64(addr-prog.Vaddr))
+			if err != nil {
+				return nil, err
+			}
+			return data, nil
+		}
+	}
+	return nil, errUnrecognizedFormat
+}
+
+func (x *elfExe) DataStart() uint64 {
+	for _, s := range x.f.Sections {
+		if s.Name == ".go.buildinfo" {
+			return s.Addr
+		}
+	}
+	for _, p := range x.f.Progs {
+		if p.Type == elf.PT_LOAD && p.Flags&(elf.PF_X|elf.PF_W) == elf.PF_W {
+			return p.Vaddr
+		}
+	}
+	return 0
+}
+
+// peExe is the PE (Windows Portable Executable) implementation of the exe interface.
+type peExe struct {
+	f *pe.File
+}
+
+func (x *peExe) imageBase() uint64 {
+	switch oh := x.f.OptionalHeader.(type) {
+	case *pe.OptionalHeader32:
+		return uint64(oh.ImageBase)
+	case *pe.OptionalHeader64:
+		return oh.ImageBase
+	}
+	return 0
+}
+
+func (x *peExe) ReadData(addr, size uint64) ([]byte, error) {
+	addr -= x.imageBase()
+	for _, sect := range x.f.Sections {
+		if uint64(sect.VirtualAddress) <= addr && addr <= uint64(sect.VirtualAddress+sect.Size-1) {
+			n := uint64(sect.VirtualAddress+sect.Size) - addr
+			if n > size {
+				n = size
+			}
+			data := make([]byte, n)
+			_, err := sect.ReadAt(data, int64(addr-uint64(sect.VirtualAddress)))
+			if err != nil {
+				return nil, errUnrecognizedFormat
+			}
+			return data, nil
+		}
+	}
+	return nil, errUnrecognizedFormat
+}
+
+func (x *peExe) DataStart() uint64 {
+	// Assume data is first writable section.
+	const (
+		IMAGE_SCN_CNT_CODE               = 0x00000020
+		IMAGE_SCN_CNT_INITIALIZED_DATA   = 0x00000040
+		IMAGE_SCN_CNT_UNINITIALIZED_DATA = 0x00000080
+		IMAGE_SCN_MEM_EXECUTE            = 0x20000000
+		IMAGE_SCN_MEM_READ               = 0x40000000
+		IMAGE_SCN_MEM_WRITE              = 0x80000000
+		IMAGE_SCN_MEM_DISCARDABLE        = 0x2000000
+		IMAGE_SCN_LNK_NRELOC_OVFL        = 0x1000000
+		IMAGE_SCN_ALIGN_32BYTES          = 0x600000
+	)
+	for _, sect := range x.f.Sections {
+		if sect.VirtualAddress != 0 && sect.Size != 0 &&
+			sect.Characteristics&^IMAGE_SCN_ALIGN_32BYTES == IMAGE_SCN_CNT_INITIALIZED_DATA|IMAGE_SCN_MEM_READ|IMAGE_SCN_MEM_WRITE {
+			return uint64(sect.VirtualAddress) + x.imageBase()
+		}
+	}
+	return 0
+}
+
+// machoExe is the Mach-O (Apple macOS/iOS) implementation of the exe interface.
+type machoExe struct {
+	f *macho.File
+}
+
+func (x *machoExe) ReadData(addr, size uint64) ([]byte, error) {
+	for _, load := range x.f.Loads {
+		seg, ok := load.(*macho.Segment)
+		if !ok {
+			continue
+		}
+		if seg.Addr <= addr && addr <= seg.Addr+seg.Filesz-1 {
+			if seg.Name == "__PAGEZERO" {
+				continue
+			}
+			n := seg.Addr + seg.Filesz - addr
+			if n > size {
+				n = size
+			}
+			data := make([]byte, n)
+			_, err := seg.ReadAt(data, int64(addr-seg.Addr))
+			if err != nil {
+				return nil, err
+			}
+			return data, nil
+		}
+	}
+	return nil, errUnrecognizedFormat
+}
+
+func (x *machoExe) DataStart() uint64 {
+	// Look for section named "__go_buildinfo".
+	for _, sec := range x.f.Sections {
+		if sec.Name == "__go_buildinfo" {
+			return sec.Addr
+		}
+	}
+	// Try the first non-empty writable segment.
+	const RW = 3
+	for _, load := range x.f.Loads {
+		seg, ok := load.(*macho.Segment)
+		if ok && seg.Addr != 0 && seg.Filesz != 0 && seg.Prot == RW && seg.Maxprot == RW {
+			return seg.Addr
+		}
+	}
+	return 0
+}
+
+// xcoffExe is the XCOFF (AIX eXtended COFF) implementation of the exe interface.
+type xcoffExe struct {
+	f *xcoff.File
+}
+
+func (x *xcoffExe) ReadData(addr, size uint64) ([]byte, error) {
+	for _, sect := range x.f.Sections {
+		if uint64(sect.VirtualAddress) <= addr && addr <= uint64(sect.VirtualAddress+sect.Size-1) {
+			n := uint64(sect.VirtualAddress+sect.Size) - addr
+			if n > size {
+				n = size
+			}
+			data := make([]byte, n)
+			_, err := sect.ReadAt(data, int64(addr-uint64(sect.VirtualAddress)))
+			if err != nil {
+				return nil, err
+			}
+			return data, nil
+		}
+	}
+	return nil, fmt.Errorf("address not mapped")
+}
+
+func (x *xcoffExe) DataStart() uint64 {
+	if s := x.f.SectionByType(xcoff.STYP_DATA); s != nil {
+		return s.VirtualAddress
+	}
+	return 0
+}