| // 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 main |
| |
| import ( |
| "bytes" |
| "flag" |
| "fmt" |
| "io" |
| "math" |
| "os" |
| ) |
| |
| var ( |
| input = flag.String("i", "", "input file") |
| output = flag.String("o", "", "output file") |
| symbol = flag.String("s", "", "symbol to inject into") |
| from = flag.String("from", "", "optional existing value of the symbol for verification") |
| value = flag.String("v", "", "value to inject into symbol") |
| |
| dump = flag.Bool("dump", false, "dump the symbol table for copying into a test") |
| ) |
| |
| var maxUint64 uint64 = math.MaxUint64 |
| |
| type cantParseError struct { |
| error |
| } |
| |
| func main() { |
| flag.Parse() |
| |
| usageError := func(s string) { |
| fmt.Fprintln(os.Stderr, s) |
| flag.Usage() |
| os.Exit(1) |
| } |
| |
| if *input == "" { |
| usageError("-i is required") |
| } |
| |
| if !*dump { |
| if *output == "" { |
| usageError("-o is required") |
| } |
| |
| if *symbol == "" { |
| usageError("-s is required") |
| } |
| |
| if *value == "" { |
| usageError("-v is required") |
| } |
| } |
| |
| r, err := os.Open(*input) |
| if err != nil { |
| fmt.Fprintln(os.Stderr, err.Error()) |
| os.Exit(2) |
| } |
| defer r.Close() |
| |
| if *dump { |
| err := dumpSymbols(r) |
| if err != nil { |
| fmt.Fprintln(os.Stderr, err.Error()) |
| os.Exit(6) |
| } |
| return |
| } |
| |
| w, err := os.OpenFile(*output, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0777) |
| if err != nil { |
| fmt.Fprintln(os.Stderr, err.Error()) |
| os.Exit(3) |
| } |
| defer w.Close() |
| |
| file, err := openFile(r) |
| if err != nil { |
| fmt.Fprintln(os.Stderr, err.Error()) |
| os.Exit(4) |
| } |
| |
| err = injectSymbol(file, w, *symbol, *value, *from) |
| if err != nil { |
| fmt.Fprintln(os.Stderr, err.Error()) |
| os.Remove(*output) |
| os.Exit(5) |
| } |
| } |
| |
| 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 injectSymbol(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)) |
| } |
| } |
| |
| return copyAndInject(file.r, w, offset, size, value) |
| } |
| |
| func copyAndInject(r io.ReaderAt, w io.Writer, offset, size uint64, value string) (err error) { |
| buf := make([]byte, size) |
| copy(buf, value) |
| |
| // 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 + size) |
| 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 |
| } |