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// Copyright 2018 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package symbol_inject
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"math"
)
var maxUint64 uint64 = math.MaxUint64
type cantParseError struct {
error
}
func OpenFile(r io.ReaderAt) (*File, error) {
file, err := elfSymbolsFromFile(r)
if elfError, ok := err.(cantParseError); ok {
// Try as a mach-o file
file, err = machoSymbolsFromFile(r)
if _, ok := err.(cantParseError); ok {
// Try as a windows PE file
file, err = peSymbolsFromFile(r)
if _, ok := err.(cantParseError); ok {
// Can't parse as elf, macho, or PE, return the elf error
return nil, elfError
}
}
}
if err != nil {
return nil, err
}
file.r = r
return file, err
}
func InjectStringSymbol(file *File, w io.Writer, symbol, value, from string) error {
offset, size, err := findSymbol(file, symbol)
if err != nil {
return err
}
if uint64(len(value))+1 > size {
return fmt.Errorf("value length %d overflows symbol size %d", len(value), size)
}
if from != "" {
// Read the exsting symbol contents and verify they match the expected value
expected := make([]byte, size)
existing := make([]byte, size)
copy(expected, from)
_, err := file.r.ReadAt(existing, int64(offset))
if err != nil {
return err
}
if bytes.Compare(existing, expected) != 0 {
return fmt.Errorf("existing symbol contents %q did not match expected value %q",
string(existing), string(expected))
}
}
buf := make([]byte, size)
copy(buf, value)
return copyAndInject(file.r, w, offset, buf)
}
func InjectUint64Symbol(file *File, w io.Writer, symbol string, value uint64) error {
offset, size, err := findSymbol(file, symbol)
if err != nil {
return err
}
if size != 8 {
return fmt.Errorf("symbol %q is not a uint64, it is %d bytes long", symbol, size)
}
buf := make([]byte, 8)
binary.LittleEndian.PutUint64(buf, value)
return copyAndInject(file.r, w, offset, buf)
}
func copyAndInject(r io.ReaderAt, w io.Writer, offset uint64, buf []byte) (err error) {
// Copy the first bytes up to the symbol offset
_, err = io.Copy(w, io.NewSectionReader(r, 0, int64(offset)))
// Write the injected value in the output file
if err == nil {
_, err = w.Write(buf)
}
// Write the remainder of the file
pos := int64(offset) + int64(len(buf))
if err == nil {
_, err = io.Copy(w, io.NewSectionReader(r, pos, 1<<63-1-pos))
}
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
func findSymbol(file *File, symbolName string) (uint64, uint64, error) {
for i, symbol := range file.Symbols {
if symbol.Name == symbolName {
// Find the next symbol (n the same section with a higher address
var n int
for n = i; n < len(file.Symbols); n++ {
if file.Symbols[n].Section != symbol.Section {
n = len(file.Symbols)
break
}
if file.Symbols[n].Addr > symbol.Addr {
break
}
}
size := symbol.Size
if size == 0 {
var end uint64
if n < len(file.Symbols) {
end = file.Symbols[n].Addr
} else {
end = symbol.Section.Size
}
if end <= symbol.Addr || end > symbol.Addr+4096 {
return maxUint64, maxUint64, fmt.Errorf("symbol end address does not seem valid, %x:%x", symbol.Addr, end)
}
size = end - symbol.Addr
}
offset := symbol.Section.Offset + symbol.Addr
return uint64(offset), uint64(size), nil
}
}
return maxUint64, maxUint64, fmt.Errorf("symbol not found")
}
type File struct {
r io.ReaderAt
Symbols []*Symbol
Sections []*Section
}
type Symbol struct {
Name string
Addr uint64 // Address of the symbol inside the section.
Size uint64 // Size of the symbol, if known.
Section *Section
}
type Section struct {
Name string
Addr uint64 // Virtual address of the start of the section.
Offset uint64 // Offset into the file of the start of the section.
Size uint64
}
func DumpSymbols(r io.ReaderAt) error {
err := dumpElfSymbols(r)
if elfError, ok := err.(cantParseError); ok {
// Try as a mach-o file
err = dumpMachoSymbols(r)
if _, ok := err.(cantParseError); ok {
// Try as a windows PE file
err = dumpPESymbols(r)
if _, ok := err.(cantParseError); ok {
// Can't parse as elf, macho, or PE, return the elf error
return elfError
}
}
}
return err
}
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