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#include <algorithm>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#ifdef __APPLE__
# include "elf.h"
#else
# include <elf.h>
#endif
#define DT_VERNEEDED 0x6ffffffe
#define DT_VERNEEDNUM 0x6fffffff
template<typename ElfHeaderType /*Elf{32,64}_Ehdr*/,
typename ElfSectionHeaderType /*Elf{32,64}_Shdr*/,
typename ElfDynamicSectionEntryType /* Elf{32,64}_Dyn */>
bool process_elf(uint8_t* bytes, size_t elf_file_size)
{
if (sizeof(ElfSectionHeaderType) > elf_file_size) {
fprintf(stderr, "ERROR: Elf header would end at %lu but file size only %lu\n", sizeof(ElfSectionHeaderType), elf_file_size);
return false;
}
ElfHeaderType* elf_hdr = reinterpret_cast<ElfHeaderType*>(bytes);
size_t last_section_header_byte = elf_hdr->e_shoff + sizeof(ElfSectionHeaderType) * elf_hdr->e_shnum;
if (last_section_header_byte > elf_file_size) {
fprintf(stderr, "ERROR: Section header would end at %lu but file size only %lu\n", last_section_header_byte, elf_file_size);
return false;
}
ElfSectionHeaderType* section_header_table = reinterpret_cast<ElfSectionHeaderType*>(bytes + elf_hdr->e_shoff);
for (unsigned int i = 1; i < elf_hdr->e_shnum; i++) {
ElfSectionHeaderType* section_header_entry = section_header_table + i;
if (section_header_entry->sh_type == SHT_DYNAMIC) {
size_t const last_dynamic_section_byte = section_header_entry->sh_offset + section_header_entry->sh_size;
if (last_dynamic_section_byte > elf_file_size) {
fprintf(stderr, "ERROR: Dynamic section would end at %lu but file size only %lu\n", last_dynamic_section_byte, elf_file_size);
return false;
}
size_t const dynamic_section_entries = section_header_entry->sh_size / sizeof(ElfDynamicSectionEntryType);
ElfDynamicSectionEntryType* const dynamic_section =
reinterpret_cast<ElfDynamicSectionEntryType*>(bytes + section_header_entry->sh_offset);
unsigned int last_nonnull_entry_idx = 0;
for (unsigned int j = dynamic_section_entries - 1; j > 0; j--) {
ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
if (dynamic_section_entry->d_tag != DT_NULL) {
last_nonnull_entry_idx = j;
break;
}
}
for (unsigned int j = 0; j < dynamic_section_entries; j++) {
ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
switch (dynamic_section_entry->d_tag) {
case DT_VERNEEDED:
case DT_VERNEEDNUM:
case DT_RPATH:
case DT_RUNPATH:
char const* removed_name;
switch (dynamic_section_entry->d_tag) {
case DT_VERNEEDED: removed_name = "DT_VERNEEDED"; break;
case DT_VERNEEDNUM: removed_name = "DT_VERNEEDNUM"; break;
case DT_RPATH: removed_name = "DT_RPATH"; break;
case DT_RUNPATH: removed_name = "DT_RUNPATH"; break;
}
printf("Removing the %s dynamic section entry\n", removed_name);
// Tag the entry with DT_NULL and put it last:
dynamic_section_entry->d_tag = DT_NULL;
// Decrease j to process new entry index:
std::swap(dynamic_section[j--], dynamic_section[last_nonnull_entry_idx--]);
break;
}
}
}
}
return true;
}
int main(int argc, char **argv)
{
if (argc < 2 || (argc == 2 && strcmp(argv[1], "-h")==0)) {
fprintf(stderr, "usage: %s <filename>\n", argv[0]);
fprintf(stderr, " Processes ELF files to remove DT_VERNEEDED, DT_VERNEEDNUM, DT_RPATH\n"
" and DT_RUNPATH entries (which the Android linker warns about)\n");
return 1;
}
for (int i = 1; i < argc; i++) {
int fd = open(argv[i], O_RDWR);
if (fd < 0) { perror("open()"); return 1; }
struct stat st;
if (fstat(fd, &st) < 0) { perror("fstat()"); return 1; }
if (st.st_size < (long long) sizeof(Elf32_Ehdr)) continue;
void* mem = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (mem == MAP_FAILED) { perror("mmap()"); return 1; }
uint8_t* bytes = reinterpret_cast<uint8_t*>(mem);
if (!(bytes[0] == 0x7F && bytes[1] == 'E' && bytes[2] == 'L' && bytes[3] == 'F')) {
munmap(mem, st.st_size);
close(fd);
continue;
}
uint8_t bit_value = bytes[4];
if (!(bit_value == 1 || bit_value == 2)) {
printf("ERROR: Incorrect bit value: %d\n", bit_value);
return 1;
} else if (bit_value == 1) {
if (!process_elf<Elf32_Ehdr, Elf32_Shdr, Elf32_Dyn>(bytes, st.st_size)) return 1;
} else {
if (!process_elf<Elf64_Ehdr, Elf64_Shdr, Elf64_Dyn>(bytes, st.st_size)) return 1;
}
if (msync(mem, st.st_size, MS_SYNC) < 0) { perror("msync()"); return 1; }
munmap(mem, st.st_size);
close(fd);
}
return 0;
}