chiark - git - mdw - termux-packages/blob - packages/termux-tools/termux-elf-cleaner.cpp

   1 #include <algorithm>
   2 #include <fcntl.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include <string.h>
   6 #include <sys/mman.h>
   7 #include <sys/stat.h>
   8 #include <sys/types.h>
   9 #include <unistd.h>
  10
  11 #ifdef __APPLE__
  12 # include "elf.h"
  13 #else
  14 # include <elf.h>
  15 #endif
  16
  17 #define DT_VERNEEDED 0x6ffffffe
  18 #define DT_VERNEEDNUM 0x6fffffff
  19
  20 template<typename ElfHeaderType /*Elf{32,64}_Ehdr*/,
  21          typename ElfSectionHeaderType /*Elf{32,64}_Shdr*/,
  22          typename ElfDynamicSectionEntryType /* Elf{32,64}_Dyn */>
  23 bool process_elf(uint8_t* bytes, size_t elf_file_size)
  24 {
  25         if (sizeof(ElfSectionHeaderType) > elf_file_size) {
  26                 fprintf(stderr, "ERROR: Elf header would end at %lu but file size only %lu\n", sizeof(ElfSectionHeaderType), elf_file_size);
  27                 return false;
  28         }
  29         ElfHeaderType* elf_hdr = reinterpret_cast<ElfHeaderType*>(bytes);
  30
  31         size_t last_section_header_byte = elf_hdr->e_shoff + sizeof(ElfSectionHeaderType) * elf_hdr->e_shnum;
  32         if (last_section_header_byte > elf_file_size) {
  33                 fprintf(stderr, "ERROR: Section header would end at %lu but file size only %lu\n", last_section_header_byte, elf_file_size);
  34                 return false;
  35         }
  36         ElfSectionHeaderType* section_header_table = reinterpret_cast<ElfSectionHeaderType*>(bytes + elf_hdr->e_shoff);
  37
  38         for (unsigned int i = 1; i < elf_hdr->e_shnum; i++) {
  39                 ElfSectionHeaderType* section_header_entry = section_header_table + i;
  40                 if (section_header_entry->sh_type == SHT_DYNAMIC) {
  41                         size_t const last_dynamic_section_byte = section_header_entry->sh_offset + section_header_entry->sh_size;
  42                         if (last_dynamic_section_byte > elf_file_size) {
  43                                 fprintf(stderr, "ERROR: Dynamic section would end at %lu but file size only %lu\n", last_dynamic_section_byte, elf_file_size);
  44                                 return false;
  45                         }
  46
  47                         size_t const dynamic_section_entries = section_header_entry->sh_size / sizeof(ElfDynamicSectionEntryType);
  48                         ElfDynamicSectionEntryType* const dynamic_section =
  49                                 reinterpret_cast<ElfDynamicSectionEntryType*>(bytes + section_header_entry->sh_offset);
  50
  51                         unsigned int last_nonnull_entry_idx = 0;
  52                         for (unsigned int j = dynamic_section_entries - 1; j > 0; j--) {
  53                                 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
  54                                 if (dynamic_section_entry->d_tag != DT_NULL) {
  55                                         last_nonnull_entry_idx = j;
  56                                         break;
  57                                 }
  58                         }
  59
  60                         for (unsigned int j = 0; j < dynamic_section_entries; j++) {
  61                                 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
  62                                 switch (dynamic_section_entry->d_tag) {
  63                                         case DT_VERNEEDED:
  64                                         case DT_VERNEEDNUM:
  65                                         case DT_RPATH:
  66                                         case DT_RUNPATH:
  67                                                 char const* removed_name;
  68                                                 switch (dynamic_section_entry->d_tag) {
  69                                                         case DT_VERNEEDED: removed_name = "DT_VERNEEDED"; break;
  70                                                         case DT_VERNEEDNUM: removed_name = "DT_VERNEEDNUM"; break;
  71                                                         case DT_RPATH: removed_name = "DT_RPATH"; break;
  72                                                         case DT_RUNPATH: removed_name = "DT_RUNPATH"; break;
  73                                                 }
  74                                                 printf("Removing the %s dynamic section entry\n", removed_name);
  75                                                 // Tag the entry with DT_NULL and put it last:
  76                                                 dynamic_section_entry->d_tag = DT_NULL;
  77                                                 // Decrease j to process new entry index:
  78                                                 std::swap(dynamic_section[j--], dynamic_section[last_nonnull_entry_idx--]);
  79                                                 break;
  80                                 }
  81                         }
  82                 }
  83         }
  84         return true;
  85 }
  86
  87
  88 int main(int argc, char **argv)
  89 {
  90         if (argc < 2 || (argc == 2 && strcmp(argv[1], "-h")==0)) {
  91                 fprintf(stderr, "usage: %s <filename>\n", argv[0]);
  92                 fprintf(stderr, "       Processes ELF files to remove DT_VERNEEDED, DT_VERNEEDNUM, DT_RPATH\n"
  93                                 "       and DT_RUNPATH entries (which the Android linker warns about)\n");
  94                 return 1;
  95         }
  96
  97         for (int i = 1; i < argc; i++) {
  98                 int fd = open(argv[i], O_RDWR);
  99                 if (fd < 0) { perror("open()"); return 1; }
 100
 101                 struct stat st;
 102                 if (fstat(fd, &st) < 0) { perror("fstat()"); return 1; }
 103
 104                 if (st.st_size < (long long) sizeof(Elf32_Ehdr)) continue;
 105
 106                 void* mem = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 107                 if (mem == MAP_FAILED) { perror("mmap()"); return 1; }
 108
 109                 uint8_t* bytes = reinterpret_cast<uint8_t*>(mem);
 110                 if (!(bytes[0] == 0x7F && bytes[1] == 'E' && bytes[2] == 'L' && bytes[3] == 'F')) {
 111                         munmap(mem, st.st_size);
 112                         close(fd);
 113                         continue;
 114                 }
 115
 116                 uint8_t bit_value = bytes[4];
 117                 if (!(bit_value == 1 || bit_value == 2)) {
 118                         printf("ERROR: Incorrect bit value: %d\n", bit_value);
 119                         return 1;
 120                 } else if (bit_value == 1) {
 121                         if (!process_elf<Elf32_Ehdr, Elf32_Shdr, Elf32_Dyn>(bytes, st.st_size)) return 1;
 122                 } else {
 123                         if (!process_elf<Elf64_Ehdr, Elf64_Shdr, Elf64_Dyn>(bytes, st.st_size)) return 1;
 124                 }
 125
 126                 if (msync(mem, st.st_size, MS_SYNC) < 0) { perror("msync()"); return 1; }
 127
 128                 munmap(mem, st.st_size);
 129                 close(fd);
 130         }
 131         return 0;
 132 }
 133