// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Verifies a host bionic executable with an embedded linker, then injects
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// the address of the _start function for the linker_wrapper to use.
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package main
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import (
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"debug/elf"
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"flag"
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"fmt"
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"io"
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"os"
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"android/soong/symbol_inject"
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)
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func main() {
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var inputFile, linkerFile, outputFile string
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flag.StringVar(&inputFile, "i", "", "Input file")
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flag.StringVar(&linkerFile, "l", "", "Linker file")
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flag.StringVar(&outputFile, "o", "", "Output file")
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flag.Parse()
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if inputFile == "" || linkerFile == "" || outputFile == "" || flag.NArg() != 0 {
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flag.Usage()
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os.Exit(1)
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}
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r, err := os.Open(inputFile)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(2)
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}
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defer r.Close()
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file, err := symbol_inject.OpenFile(r)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(3)
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}
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linker, err := elf.Open(linkerFile)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(4)
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}
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start_addr, err := parseElf(r, linker)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(5)
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}
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w, err := os.OpenFile(outputFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0777)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(6)
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}
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defer w.Close()
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err = symbol_inject.InjectUint64Symbol(file, w, "__dlwrap_original_start", start_addr)
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if err != nil {
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fmt.Fprintln(os.Stderr, err.Error())
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os.Exit(7)
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}
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}
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// Check the ELF file, and return the address to the _start function
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func parseElf(r io.ReaderAt, linker *elf.File) (uint64, error) {
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file, err := elf.NewFile(r)
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if err != nil {
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return 0, err
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}
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symbols, err := file.Symbols()
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if err != nil {
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return 0, err
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}
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for _, prog := range file.Progs {
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if prog.Type == elf.PT_INTERP {
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return 0, fmt.Errorf("File should not have a PT_INTERP header")
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}
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}
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if dlwrap_start, err := findSymbol(symbols, "__dlwrap__start"); err != nil {
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return 0, err
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} else if dlwrap_start.Value != file.Entry {
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return 0, fmt.Errorf("Expected file entry(0x%x) to point to __dlwrap_start(0x%x)",
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file.Entry, dlwrap_start.Value)
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}
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err = checkLinker(file, linker, symbols)
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if err != nil {
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return 0, err
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}
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start, err := findSymbol(symbols, "_start")
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if err != nil {
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return 0, fmt.Errorf("Failed to find _start symbol")
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}
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return start.Value, nil
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}
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func findSymbol(symbols []elf.Symbol, name string) (elf.Symbol, error) {
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for _, sym := range symbols {
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if sym.Name == name {
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return sym, nil
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}
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}
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return elf.Symbol{}, fmt.Errorf("Failed to find symbol %q", name)
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}
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// Check that all of the PT_LOAD segments have been embedded properly
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func checkLinker(file, linker *elf.File, fileSyms []elf.Symbol) error {
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dlwrap_linker_offset, err := findSymbol(fileSyms, "__dlwrap_linker_offset")
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if err != nil {
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return err
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}
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for i, lprog := range linker.Progs {
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if lprog.Type != elf.PT_LOAD {
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continue
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}
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laddr := lprog.Vaddr + dlwrap_linker_offset.Value
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found := false
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for _, prog := range file.Progs {
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if prog.Type != elf.PT_LOAD {
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continue
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}
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if laddr < prog.Vaddr || laddr > prog.Vaddr+prog.Memsz {
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continue
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}
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found = true
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if lprog.Flags != prog.Flags {
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return fmt.Errorf("Linker prog %d (0x%x) flags (%s) do not match (%s)",
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i, lprog.Vaddr, lprog.Flags, prog.Flags)
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}
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if laddr+lprog.Memsz > prog.Vaddr+prog.Filesz {
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return fmt.Errorf("Linker prog %d (0x%x) not fully present (0x%x > 0x%x)",
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i, lprog.Vaddr, laddr+lprog.Memsz, prog.Vaddr+prog.Filesz)
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}
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}
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if !found {
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return fmt.Errorf("Linker prog %d (0x%x) not found at offset 0x%x",
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i, lprog.Vaddr, dlwrap_linker_offset.Value)
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}
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}
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return nil
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}
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