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_VERSYM 0x6ffffff0
  18 #define DT_VERNEEDED 0x6ffffffe
  19 #define DT_VERNEEDNUM 0x6fffffff
  20
  21 template<typename ElfHeaderType /*Elf{32,64}_Ehdr*/,
  22          typename ElfSectionHeaderType /*Elf{32,64}_Shdr*/,
  23          typename ElfDynamicSectionEntryType /* Elf{32,64}_Dyn */>
  24 bool process_elf(uint8_t* bytes, size_t elf_file_size, char const* file_name)
  25 {
  26         if (sizeof(ElfSectionHeaderType) > elf_file_size) {
  27                 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);
  28                 return false;
  29         }
  30         ElfHeaderType* elf_hdr = reinterpret_cast<ElfHeaderType*>(bytes);
  31
  32         size_t last_section_header_byte = elf_hdr->e_shoff + sizeof(ElfSectionHeaderType) * elf_hdr->e_shnum;
  33         if (last_section_header_byte > elf_file_size) {
  34                 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);
  35                 return false;
  36         }
  37         ElfSectionHeaderType* section_header_table = reinterpret_cast<ElfSectionHeaderType*>(bytes + elf_hdr->e_shoff);
  38
  39         for (unsigned int i = 1; i < elf_hdr->e_shnum; i++) {
  40                 ElfSectionHeaderType* section_header_entry = section_header_table + i;
  41                 if (section_header_entry->sh_type == SHT_DYNAMIC) {
  42                         size_t const last_dynamic_section_byte = section_header_entry->sh_offset + section_header_entry->sh_size;
  43                         if (last_dynamic_section_byte > elf_file_size) {
  44                                 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);
  45                                 return false;
  46                         }
  47
  48                         size_t const dynamic_section_entries = section_header_entry->sh_size / sizeof(ElfDynamicSectionEntryType);
  49                         ElfDynamicSectionEntryType* const dynamic_section =
  50                                 reinterpret_cast<ElfDynamicSectionEntryType*>(bytes + section_header_entry->sh_offset);
  51
  52                         unsigned int last_nonnull_entry_idx = 0;
  53                         for (unsigned int j = dynamic_section_entries - 1; j > 0; j--) {
  54                                 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
  55                                 if (dynamic_section_entry->d_tag != DT_NULL) {
  56                                         last_nonnull_entry_idx = j;
  57                                         break;
  58                                 }
  59                         }
  60
  61                         for (unsigned int j = 0; j < dynamic_section_entries; j++) {
  62                                 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
  63                                 char const* removed_name = nullptr;
  64                                 switch (dynamic_section_entry->d_tag) {
  65                                         case DT_VERSYM: removed_name = "DT_VERSYM"; break;
  66                                         case DT_VERNEEDED: removed_name = "DT_VERNEEDED"; break;
  67                                         case DT_VERNEEDNUM: removed_name = "DT_VERNEEDNUM"; break;
  68                                         case DT_VERDEF: removed_name = "DT_VERDEF"; break;
  69                                         case DT_VERDEFNUM: removed_name = "DT_VERDEFNUM"; break;
  70                                         case DT_RPATH: removed_name = "DT_RPATH"; break;
  71                                         case DT_RUNPATH: removed_name = "DT_RUNPATH"; break;
  72                                 }
  73                                 if (removed_name != nullptr) {
  74                                         printf("termux-elf-cleaner: Removing the %s dynamic section entry from '%s'\n", removed_name, file_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                                 }
  80                         }
  81                 } else if (section_header_entry->sh_type == SHT_GNU_verdef ||
  82                            section_header_entry->sh_type == SHT_GNU_verneed ||
  83                            section_header_entry->sh_type == SHT_GNU_versym) {
  84                         printf("termux-elf-cleaner: Removing version section from '%s'\n", file_name);
  85                         section_header_entry->sh_type = SHT_NULL;
  86                 }
  87         }
  88         return true;
  89 }
  90
  91
  92 int main(int argc, char const** argv)
  93 {
  94         if (argc < 2 || (argc == 2 && strcmp(argv[1], "-h")==0)) {
  95                 fprintf(stderr, "usage: %s <filename>\n", argv[0]);
  96                 fprintf(stderr, "       Processes ELF files to remove DT_VERNEEDED, DT_VERNEEDNUM, DT_RPATH\n"
  97                                 "       and DT_RUNPATH entries (which the Android linker warns about)\n");
  98                 return 1;
  99         }
 100
 101         for (int i = 1; i < argc; i++) {
 102                 char const* file_name = argv[i];
 103                 int fd = open(file_name, O_RDWR);
 104                 if (fd < 0) {
 105                         char* error_message;
 106                         if (asprintf(&error_message, "open(\"%s\")", file_name) == -1) error_message = (char*) "open()";
 107                         perror(error_message);
 108                         return 1;
 109                 }
 110
 111                 struct stat st;
 112                 if (fstat(fd, &st) < 0) { perror("fstat()"); return 1; }
 113
 114                 if (st.st_size < (long long) sizeof(Elf32_Ehdr)) {
 115                         close(fd);
 116                         continue;
 117                 }
 118
 119                 void* mem = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 120                 if (mem == MAP_FAILED) { perror("mmap()"); return 1; }
 121
 122                 uint8_t* bytes = reinterpret_cast<uint8_t*>(mem);
 123                 if (!(bytes[0] == 0x7F && bytes[1] == 'E' && bytes[2] == 'L' && bytes[3] == 'F')) {
 124                         // Not the ELF magic number.
 125                         munmap(mem, st.st_size);
 126                         close(fd);
 127                         continue;
 128                 }
 129
 130                 if (bytes[/*EI_DATA*/5] != 1) {
 131                         fprintf(stderr, "termux-elf-cleaner: Not little endianness in '%s'\n", file_name);
 132                         munmap(mem, st.st_size);
 133                         close(fd);
 134                         continue;
 135                 }
 136
 137                 uint8_t const bit_value = bytes[/*EI_CLASS*/4];
 138                 if (bit_value == 1) {
 139                         if (!process_elf<Elf32_Ehdr, Elf32_Shdr, Elf32_Dyn>(bytes, st.st_size, file_name)) return 1;
 140                 } else if (bit_value == 2) {
 141                         if (!process_elf<Elf64_Ehdr, Elf64_Shdr, Elf64_Dyn>(bytes, st.st_size, file_name)) return 1;
 142                 } else {
 143                         printf("termux-elf-cleaner: Incorrect bit value %d in '%s'\n", bit_value, file_name);
 144                         return 1;
 145                 }
 146
 147                 if (msync(mem, st.st_size, MS_SYNC) < 0) { perror("msync()"); return 1; }
 148
 149                 munmap(mem, st.st_size);
 150                 close(fd);
 151         }
 152         return 0;
 153 }
 154