chiark - git - mdw - termux-packages/blob - packages/termux-elf-cleaner/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, char const* file_name)
  24 {
  25         if (sizeof(ElfSectionHeaderType) > elf_file_size) {
  26                 fprintf(stderr, "termux-elf-cleaner: Elf header for '%s' would end at %zu but file size only %zu\n", file_name, 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, "termux-elf-cleaner: Section header for '%s' would end at %zu but file size only %zu\n", file_name, 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, "termux-elf-cleaner: Dynamic section for '%s' would end at %zu but file size only %zu\n", file_name, 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                                 char const* removed_name = nullptr;
  63                                 switch (dynamic_section_entry->d_tag) {
  64                                         case DT_VERNEEDED: removed_name = "DT_VERNEEDED"; break;
  65                                         case DT_VERNEEDNUM: removed_name = "DT_VERNEEDNUM"; break;
  66                                         case DT_VERDEF: removed_name = "DT_VERDEF"; break;
  67                                         case DT_VERDEFNUM: removed_name = "DT_VERDEFNUM"; break;
  68                                         case DT_RPATH: removed_name = "DT_RPATH"; break;
  69                                         case DT_RUNPATH: removed_name = "DT_RUNPATH"; break;
  70                                 }
  71                                 if (removed_name != nullptr) {
  72                                         printf("termux-elf-cleaner: Removing the %s dynamic section entry from '%s'\n", removed_name, file_name);
  73                                         // Tag the entry with DT_NULL and put it last:
  74                                         dynamic_section_entry->d_tag = DT_NULL;
  75                                         // Decrease j to process new entry index:
  76                                         std::swap(dynamic_section[j--], dynamic_section[last_nonnull_entry_idx--]);
  77                                 }
  78                         }
  79                 }
  80         }
  81         return true;
  82 }
  83
  84
  85 int main(int argc, char const** argv)
  86 {
  87         if (argc < 2 || (argc == 2 && strcmp(argv[1], "-h")==0)) {
  88                 fprintf(stderr, "usage: %s <filename>\n", argv[0]);
  89                 fprintf(stderr, "       Processes ELF files to remove DT_VERNEEDED, DT_VERNEEDNUM, DT_RPATH\n"
  90                                 "       and DT_RUNPATH entries (which the Android linker warns about)\n");
  91                 return 1;
  92         }
  93
  94         for (int i = 1; i < argc; i++) {
  95                 char const* file_name = argv[i];
  96                 int fd = open(file_name, O_RDWR);
  97                 if (fd < 0) {
  98                         char* error_message;
  99                         if (asprintf(&error_message, "open(\"%s\")", file_name) == -1) error_message = (char*) "open()";
 100                         perror(error_message);
 101                         return 1;
 102                 }
 103
 104                 struct stat st;
 105                 if (fstat(fd, &st) < 0) { perror("fstat()"); return 1; }
 106
 107                 if (st.st_size < (long long) sizeof(Elf32_Ehdr)) {
 108                         close(fd);
 109                         continue;
 110                 }
 111
 112                 void* mem = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 113                 if (mem == MAP_FAILED) { perror("mmap()"); return 1; }
 114
 115                 uint8_t* bytes = reinterpret_cast<uint8_t*>(mem);
 116                 if (!(bytes[0] == 0x7F && bytes[1] == 'E' && bytes[2] == 'L' && bytes[3] == 'F')) {
 117                         // Not the ELF magic number.
 118                         munmap(mem, st.st_size);
 119                         close(fd);
 120                         continue;
 121                 }
 122
 123                 if (bytes[/*EI_DATA*/5] != 1) {
 124                         fprintf(stderr, "termux-elf-cleaner: Not little endianness in '%s'\n", file_name);
 125                         munmap(mem, st.st_size);
 126                         close(fd);
 127                         continue;
 128                 }
 129
 130                 uint8_t const bit_value = bytes[/*EI_CLASS*/4];
 131                 if (bit_value == 1) {
 132                         if (!process_elf<Elf32_Ehdr, Elf32_Shdr, Elf32_Dyn>(bytes, st.st_size, file_name)) return 1;
 133                 } else if (bit_value == 2) {
 134                         if (!process_elf<Elf64_Ehdr, Elf64_Shdr, Elf64_Dyn>(bytes, st.st_size, file_name)) return 1;
 135                 } else {
 136                         printf("termux-elf-cleaner: Incorrect bit value %d in '%s'\n", bit_value, file_name);
 137                         return 1;
 138                 }
 139
 140                 if (msync(mem, st.st_size, MS_SYNC) < 0) { perror("msync()"); return 1; }
 141
 142                 munmap(mem, st.st_size);
 143                 close(fd);
 144         }
 145         return 0;
 146 }
 147