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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // Tool to pack and unpack relative relocations in a shared library.
      6 //
      7 // Invoke with -v to trace actions taken when packing or unpacking.
      8 // Invoke with -p to pad removed relocations with R_*_NONE.  Suppresses
      9 // shrinking of .rel.dyn.
     10 // See PrintUsage() below for full usage details.
     11 //
     12 // NOTE: Breaks with libelf 0.152, which is buggy.  libelf 0.158 works.
     13 
     14 #include <errno.h>
     15 #include <fcntl.h>
     16 #include <getopt.h>
     17 #include <stdio.h>
     18 #include <stdlib.h>
     19 #include <sys/types.h>
     20 #include <unistd.h>
     21 #include <string>
     22 
     23 #include "debug.h"
     24 #include "elf_file.h"
     25 #include "elf_traits.h"
     26 #include "libelf.h"
     27 
     28 #include "nativehelper/ScopedFd.h"
     29 
     30 static void PrintUsage(const char* argv0) {
     31   std::string temporary = argv0;
     32   const size_t last_slash = temporary.find_last_of("/");
     33   if (last_slash != temporary.npos) {
     34     temporary.erase(0, last_slash + 1);
     35   }
     36   const char* basename = temporary.c_str();
     37 
     38   printf(
     39       "Usage: %s [-u] [-v] [-p] file\n\n"
     40       "Pack or unpack relative relocations in a shared library.\n\n"
     41       "  -u, --unpack   unpack previously packed relative relocations\n"
     42       "  -v, --verbose  trace object file modifications (for debugging)\n"
     43       "  -p, --pad      do not shrink relocations, but pad (for debugging)\n\n",
     44       basename);
     45 
     46   printf(
     47       "Debug sections are not handled, so packing should not be used on\n"
     48       "shared libraries compiled for debugging or otherwise unstripped.\n");
     49 }
     50 
     51 int main(int argc, char* argv[]) {
     52   bool is_unpacking = false;
     53   bool is_verbose = false;
     54   bool is_padding = false;
     55 
     56   static const option options[] = {
     57     {"unpack", 0, 0, 'u'}, {"verbose", 0, 0, 'v'}, {"pad", 0, 0, 'p'},
     58     {"help", 0, 0, 'h'}, {NULL, 0, 0, 0}
     59   };
     60   bool has_options = true;
     61   while (has_options) {
     62     int c = getopt_long(argc, argv, "uvph", options, NULL);
     63     switch (c) {
     64       case 'u':
     65         is_unpacking = true;
     66         break;
     67       case 'v':
     68         is_verbose = true;
     69         break;
     70       case 'p':
     71         is_padding = true;
     72         break;
     73       case 'h':
     74         PrintUsage(argv[0]);
     75         return 0;
     76       case '?':
     77         LOG(INFO) << "Try '" << argv[0] << " --help' for more information.";
     78         return 1;
     79       case -1:
     80         has_options = false;
     81         break;
     82       default:
     83         NOTREACHED();
     84         return 1;
     85     }
     86   }
     87   if (optind != argc - 1) {
     88     LOG(INFO) << "Try '" << argv[0] << " --help' for more information.";
     89     return 1;
     90   }
     91 
     92   if (elf_version(EV_CURRENT) == EV_NONE) {
     93     LOG(WARNING) << "Elf Library is out of date!";
     94   }
     95 
     96   const char* file = argv[argc - 1];
     97   ScopedFd fd(open(file, O_RDWR));
     98   if (fd.get() == -1) {
     99     LOG(ERROR) << file << ": " << strerror(errno);
    100     return 1;
    101   }
    102 
    103   if (is_verbose)
    104     relocation_packer::Logger::SetVerbose(1);
    105 
    106   // We need to detect elf class in order to create
    107   // correct implementation
    108   uint8_t e_ident[EI_NIDENT];
    109   if (TEMP_FAILURE_RETRY(read(fd.get(), e_ident, EI_NIDENT) != EI_NIDENT)) {
    110     LOG(ERROR) << file << ": failed to read elf header:" << strerror(errno);
    111     return 1;
    112   }
    113 
    114   if (TEMP_FAILURE_RETRY(lseek(fd.get(), 0, SEEK_SET)) != 0) {
    115     LOG(ERROR) << file << ": lseek to 0 failed:" << strerror(errno);
    116     return 1;
    117   }
    118 
    119   bool status = false;
    120 
    121   if (e_ident[EI_CLASS] == ELFCLASS32) {
    122     relocation_packer::ElfFile<ELF32_traits> elf_file(fd.get());
    123     elf_file.SetPadding(is_padding);
    124 
    125     if (is_unpacking) {
    126       status = elf_file.UnpackRelocations();
    127     } else {
    128       status = elf_file.PackRelocations();
    129     }
    130   } else if (e_ident[EI_CLASS] == ELFCLASS64) {
    131     relocation_packer::ElfFile<ELF64_traits> elf_file(fd.get());
    132     elf_file.SetPadding(is_padding);
    133 
    134     if (is_unpacking) {
    135       status = elf_file.UnpackRelocations();
    136     } else {
    137       status = elf_file.PackRelocations();
    138     }
    139   } else {
    140     LOG(ERROR) << file << ": unknown ELFCLASS: " << e_ident[EI_CLASS];
    141     return 1;
    142   }
    143 
    144   if (!status) {
    145     LOG(ERROR) << file << ": failed to pack/unpack file";
    146     return 1;
    147   }
    148 
    149   return 0;
    150 }
    151