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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
- IsMachoFile bool
- }
- 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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