int main(int argc, char **argv) {
argc--, argv++;
if (!argc)
return 0;
/* Check to see whether the ELF library is current. */
FAILIF (elf_version(EV_CURRENT) == EV_NONE, "libelf is out of date!\n");
const char *filename;
for (; argc; argc--) {
filename = *argv++;
Elf *elf;
GElf_Ehdr elf_hdr;
int fd;
int prelinked;
long prelink_addr = 0;
INFO("Processing file [%s]\n", filename);
fd = open(filename, O_RDONLY);
FAILIF(fd < 0, "open(%d): %s (%d).\n",
filename,
strerror(errno),
errno);
elf = elf_begin(fd, ELF_C_READ_MMAP_PRIVATE, NULL);
FAILIF_LIBELF(elf == NULL, elf_begin);
FAILIF_LIBELF(0 == gelf_getehdr(elf, &elf_hdr),
gelf_getehdr);
#ifdef SUPPORT_ANDROID_PRELINK_TAGS
prelinked = check_prelinked(filename, elf_hdr.e_ident[EI_DATA] == ELFDATA2LSB,
&prelink_addr);
#else
#error 'SUPPORT_ANDROID_PRELINK_TAGS is not defined!'
#endif
if (prelinked)
PRINT("%s: 0x%08x\n", filename, prelink_addr);
else
PRINT("%s: not prelinked\n", filename);
FAILIF_LIBELF(elf_end(elf), elf_end);
close(fd);
}
return 0;
}
int hash_lookup(Elf *elf,
section_info_t *hash_info,
section_info_t *symtab_info,
const char *symname,
GElf_Sym *sym_mem)
{
Elf32_Word *hash_data = (Elf32_Word *)hash_info->data->d_buf;
Elf32_Word index;
Elf32_Word nbuckets = *hash_data++;
Elf32_Word *buckets = ++hash_data;
Elf32_Word *chains = hash_data + nbuckets;
GElf_Sym *sym;
index = buckets[elf_hash(symname) % nbuckets];
while(index != STN_UNDEF)
{
sym = gelf_getsymshndx (symtab_info->data, NULL, index, sym_mem, NULL);
FAILIF_LIBELF(NULL == sym, gelf_getsymshndx);
if (!strcmp(symname,
elf_strptr(elf, symtab_info->hdr->sh_link, sym->st_name)))
break;
index = chains[index];
}
return index;
}
void clone_elf(Elf *elf, Elf *newelf,
const char *elf_name,
const char *newelf_name,
bool *sym_filter, int num_symbols,
int shady
#ifdef SUPPORT_ANDROID_PRELINK_TAGS
, int *prelinked,
int *elf_little,
long *prelink_addr
#endif
, bool rebuild_shstrtab,
bool strip_debug,
bool dry_run)
{
GElf_Ehdr ehdr_mem, *ehdr; /* store ELF header of original library */
size_t shstrndx; /* section-strings-section index */
size_t shnum; /* number of sections in the original file */
/* string table for section headers in new file */
struct Ebl_Strtab *shst = NULL;
int dynamic_idx = -1; /* index in shdr_info[] of .dynamic section */
int dynsym_idx = -1; /* index in shdr_info[] of dynamic symbol table
section */
unsigned int cnt; /* general-purpose counter */
/* This flag is true when at least one section is dropped or when the
relative order of sections has changed, so that section indices in
the resulting file will be different from those in the original. */
bool sections_dropped_or_rearranged;
Elf_Scn *scn; /* general-purpose section */
size_t idx; /* general-purporse section index */
shdr_info_t *shdr_info = NULL;
unsigned int shdr_info_len = 0;
GElf_Phdr *phdr_info = NULL;
/* Get the information from the old file. */
ehdr = gelf_getehdr (elf, &ehdr_mem);
FAILIF_LIBELF(NULL == ehdr, gelf_getehdr);
/* Create new program header for the elf file */
FAILIF(gelf_newehdr (newelf, gelf_getclass (elf)) == 0 ||
(ehdr->e_type != ET_REL && gelf_newphdr (newelf,
ehdr->e_phnum) == 0),
"Cannot create new file: %s", elf_errmsg (-1));
#ifdef SUPPORT_ANDROID_PRELINK_TAGS
ASSERT(prelinked);
ASSERT(prelink_addr);
ASSERT(elf_little);
*elf_little = (ehdr->e_ident[EI_DATA] == ELFDATA2LSB);
*prelinked = check_prelinked(elf_name, *elf_little, prelink_addr);
#endif
INFO("\n\nCALCULATING MODIFICATIONS\n\n");
/* Copy out the old program header: notice that if the ELF file does not
have a program header, this loop won't execute.
*/
INFO("Copying ELF program header...\n");
phdr_info = (GElf_Phdr *)CALLOC(ehdr->e_phnum, sizeof(GElf_Phdr));
for (cnt = 0; cnt < ehdr->e_phnum; ++cnt) {
INFO("\tRetrieving entry %d\n", cnt);
FAILIF_LIBELF(NULL == gelf_getphdr(elf, cnt, phdr_info + cnt),
gelf_getphdr);
/* -- we update the header at the end
FAILIF_LIBELF(gelf_update_phdr (newelf, cnt, phdr_info + cnt) == 0,
gelf_update_phdr);
*/
}
/* Get the section-header strings section. This section contains the
strings used to name the other sections. */
FAILIF_LIBELF(elf_getshstrndx(elf, &shstrndx) < 0, elf_getshstrndx);
/* Get the number of sections. */
FAILIF_LIBELF(elf_getshnum (elf, &shnum) < 0, elf_getshnum);
INFO("Original ELF file has %zd sections.\n", shnum);
/* Allocate the section-header-info buffer. We allocate one more entry
for the section-strings section because we regenerate that one and
place it at the very end of the file. Note that just because we create
an extra entry in the shdr_info array, it does not mean that we create
one more section the header. We just mark the old section for removal
and create one as the last section.
*/
INFO("Allocating section-header info structure (%zd) bytes...\n",
shnum*sizeof (shdr_info_t));
shdr_info_len = rebuild_shstrtab ? shnum + 1 : shnum;
shdr_info = (shdr_info_t *)CALLOC(shdr_info_len, sizeof (shdr_info_t));
/* Iterate over all the sections and initialize the internal section-info
array...
*/
INFO("Initializing section-header info structure...\n");
/* Gather information about the sections in this file. */
scn = NULL;
cnt = 1;
while ((scn = elf_nextscn (elf, scn)) != NULL) {
ASSERT(elf_ndxscn(scn) == cnt);
shdr_info[cnt].scn = scn;
FAILIF_LIBELF(NULL == gelf_getshdr(scn, &shdr_info[cnt].shdr),
gelf_getshdr);
/* Get the name of the section. */
shdr_info[cnt].name = elf_strptr (elf, shstrndx,
shdr_info[cnt].shdr.sh_name);
INFO("\tname: %s\n", shdr_info[cnt].name);
FAILIF(shdr_info[cnt].name == NULL,
"Malformed file: section %d name is null\n",
cnt);
/* Mark them as present but not yet investigated. By "investigating"
sections, we mean that we check to see if by stripping other
sections, the sections under investigation will be compromised. For
example, if we are removing a section of code, then we want to make
sure that the symbol table does not contain symbols that refer to
this code, so we investigate the symbol table. If we do find such
symbols, we will not strip the code section.
*/
shdr_info[cnt].idx = 1;
/* Remember the shdr.sh_link value. We need to remember this value
for those sections that refer to other sections. For example,
we need to remember it for relocation-entry sections, because if
we modify the symbol table that a relocation-entry section is
relative to, then we need to patch the relocation section. By the
time we get to deciding whether we need to patch the relocation
section, we will have overwritten its header's sh_link field with
a new value.
*/
shdr_info[cnt].old_shdr = shdr_info[cnt].shdr;
INFO("\t\toriginal sh_link: %08d\n", shdr_info[cnt].old_shdr.sh_link);
INFO("\t\toriginal sh_addr: %lld\n", shdr_info[cnt].old_shdr.sh_addr);
INFO("\t\toriginal sh_offset: %lld\n",
shdr_info[cnt].old_shdr.sh_offset);
INFO("\t\toriginal sh_size: %lld\n", shdr_info[cnt].old_shdr.sh_size);
if (shdr_info[cnt].shdr.sh_type == SHT_DYNAMIC) {
INFO("\t\tthis is the SHT_DYNAMIC section [%s] at index %d\n",
shdr_info[cnt].name,
cnt);
dynamic_idx = cnt;
}
else if (shdr_info[cnt].shdr.sh_type == SHT_DYNSYM) {
INFO("\t\tthis is the SHT_DYNSYM section [%s] at index %d\n",
shdr_info[cnt].name,
cnt);
dynsym_idx = cnt;
}
FAILIF(shdr_info[cnt].shdr.sh_type == SHT_SYMTAB_SHNDX,
"Cannot handle sh_type SHT_SYMTAB_SHNDX!\n");
FAILIF(shdr_info[cnt].shdr.sh_type == SHT_GROUP,
"Cannot handle sh_type SHT_GROUP!\n");
FAILIF(shdr_info[cnt].shdr.sh_type == SHT_GNU_versym,
"Cannot handle sh_type SHT_GNU_versym!\n");
/* Increment the counter. */
++cnt;
} /* while */
/* Get the EBL handling. */
Ebl *ebl = ebl_openbackend (elf);
FAILIF_LIBELF(NULL == ebl, ebl_openbackend);
FAILIF_LIBELF(0 != arm_init(elf, ehdr->e_machine, ebl, sizeof(Ebl)),
arm_init);
if (strip_debug) {
/* This will actually strip more than just sections. It will strip
anything not essential to running the image.
*/
INFO("Finding debug sections to strip.\n");
/* Now determine which sections can go away. The general rule is that
all sections which are not used at runtime are stripped out. But
there are a few exceptions:
- special sections named ".comment" and ".note" are kept
- OS or architecture specific sections are kept since we might not
know how to handle them
- if a section is referred to from a section which is not removed
in the sh_link or sh_info element it cannot be removed either
*/
for (cnt = 1; cnt < shnum; ++cnt) {
/* Check whether the section can be removed. */
if (SECTION_STRIP_P (ebl, elf, ehdr, &shdr_info[cnt].shdr,
shdr_info[cnt].name,
1, /* remove .comment sections */
1 /* remove all debug sections */) ||
/* The macro above is broken--check for .comment explicitly */
!strcmp(".comment", shdr_info[cnt].name)
#ifdef ARM_SPECIFIC_HACKS
||
/* We ignore this section, that's why we can remove it. */
!strcmp(".stack", shdr_info[cnt].name)
#endif
)
{
/* For now assume this section will be removed. */
INFO("Section [%s] will be stripped from image.\n",
shdr_info[cnt].name);
shdr_info[cnt].idx = 0;
}
#ifdef STRIP_STATIC_SYMBOLS
else if (shdr_info[cnt].shdr.sh_type == SHT_SYMTAB) {
/* Mark the static symbol table for removal */
INFO("Section [%s] (static symbol table) will be stripped from image.\n",
shdr_info[cnt].name);
shdr_info[cnt].idx = 0;
if (shdr_info[shdr_info[cnt].shdr.sh_link].shdr.sh_type ==
SHT_STRTAB)
{
/* Mark the symbol table's string table for removal. */
INFO("Section [%s] (static symbol-string table) will be stripped from image.\n",
shdr_info[shdr_info[cnt].shdr.sh_link].name);
shdr_info[shdr_info[cnt].shdr.sh_link].idx = 0;
}
else {
ERROR("Expecting the sh_link field of a symbol table to point to"
" associated symbol-strings table! This is not mandated by"
" the standard, but is a common practice and the only way "
" to know for sure which strings table corresponds to which"
" symbol table!\n");
}
}
#endif
}
/* Mark the SHT_NULL section as handled. */
shdr_info[0].idx = 2;
/* Handle exceptions: section groups and cross-references. We might have
to repeat this a few times since the resetting of the flag might
propagate.
*/
int exceptions_pass = 0;
bool changes;
do {
changes = false;
INFO("\nHandling exceptions, pass %d\n\n", exceptions_pass++);
for (cnt = 1; cnt < shnum; ++cnt) {
if (shdr_info[cnt].idx == 0) {
/* If a relocation section is marked as being removed but the
section it is relocating is not, then do not remove the
relocation section.
*/
if ((shdr_info[cnt].shdr.sh_type == SHT_REL
|| shdr_info[cnt].shdr.sh_type == SHT_RELA)
&& shdr_info[shdr_info[cnt].shdr.sh_info].idx != 0) {
PRINT("\tSection [%s] will not be removed because the "
"section it is relocating (%s) stays.\n",
shdr_info[cnt].name,
shdr_info[shdr_info[cnt].shdr.sh_info].name);
}
}
if (shdr_info[cnt].idx == 1) {
INFO("Processing section [%s]...\n", shdr_info[cnt].name);
/* The content of symbol tables we don't remove must not
reference any section which we do remove. Otherwise
we cannot remove the referred section.
*/
if (shdr_info[cnt].shdr.sh_type == SHT_DYNSYM ||
shdr_info[cnt].shdr.sh_type == SHT_SYMTAB)
{
Elf_Data *symdata;
size_t elsize;
INFO("\tSection [%s] is a symbol table that's not being"
" removed.\n\tChecking to make sure that no symbols"
" refer to sections that are being removed.\n",
shdr_info[cnt].name);
/* Make sure the data is loaded. */
symdata = elf_getdata (shdr_info[cnt].scn, NULL);
FAILIF_LIBELF(NULL == symdata, elf_getdata);
/* Go through all symbols and make sure the section they
reference is not removed. */
elsize = gelf_fsize (elf, ELF_T_SYM, 1, ehdr->e_version);
/* Check the length of the dynamic-symbol filter. */
FAILIF(sym_filter != NULL &&
(size_t)num_symbols != symdata->d_size / elsize,
"Length of dynsym filter (%d) must equal the number"
" of dynamic symbols (%zd)!\n",
num_symbols,
symdata->d_size / elsize);
size_t inner;
for (inner = 0;
inner < symdata->d_size / elsize;
++inner)
{
GElf_Sym sym_mem;
GElf_Sym *sym;
size_t scnidx;
sym = gelf_getsymshndx (symdata, NULL,
inner, &sym_mem, NULL);
FAILIF_LIBELF(sym == NULL, gelf_getsymshndx);
scnidx = sym->st_shndx;
FAILIF(scnidx == SHN_XINDEX,
"Can't handle SHN_XINDEX!\n");
if (scnidx == SHN_UNDEF ||
scnidx >= shnum ||
(scnidx >= SHN_LORESERVE &&
scnidx <= SHN_HIRESERVE) ||
GELF_ST_TYPE (sym->st_info) == STT_SECTION)
{
continue;
}
/* If the symbol is going to be thrown and it is a
global or weak symbol that is defined (not imported),
then continue. Since the symbol is going away, we
do not care whether it refers to a section that is
also going away.
*/
if (sym_filter && !sym_filter[inner])
{
bool global_or_weak =
ELF32_ST_BIND(sym->st_info) == STB_GLOBAL ||
ELF32_ST_BIND(sym->st_info) == STB_WEAK;
if (!global_or_weak && sym->st_shndx != SHN_UNDEF)
continue;
}
/* -- far too much output
INFO("\t\t\tSymbol [%s] (%d)\n",
elf_strptr(elf,
shdr_info[cnt].shdr.sh_link,
sym->st_name),
shdr_info[cnt].shdr.sh_info);
*/
if (shdr_info[scnidx].idx == 0)
{
PRINT("\t\t\tSymbol [%s] refers to section [%s], "
"which is being removed. Will keep that "
"section.\n",
elf_strptr(elf,
shdr_info[cnt].shdr.sh_link,
sym->st_name),
shdr_info[scnidx].name);
/* Mark this section as used. */
shdr_info[scnidx].idx = 1;
changes |= scnidx < cnt;
}
} /* for each symbol */
} /* section type is SHT_DYNSYM or SHT_SYMTAB */
/* Cross referencing happens:
- for the cases the ELF specification says. That are
+ SHT_DYNAMIC in sh_link to string table
+ SHT_HASH in sh_link to symbol table
+ SHT_REL and SHT_RELA in sh_link to symbol table
+ SHT_SYMTAB and SHT_DYNSYM in sh_link to string table
+ SHT_GROUP in sh_link to symbol table
+ SHT_SYMTAB_SHNDX in sh_link to symbol table
Other (OS or architecture-specific) sections might as
well use this field so we process it unconditionally.
- references inside section groups
- specially marked references in sh_info if the SHF_INFO_LINK
flag is set
*/
if (shdr_info[shdr_info[cnt].shdr.sh_link].idx == 0) {
shdr_info[shdr_info[cnt].shdr.sh_link].idx = 1;
changes |= shdr_info[cnt].shdr.sh_link < cnt;
}
/* Handle references through sh_info. */
if (SH_INFO_LINK_P (&shdr_info[cnt].shdr) &&
shdr_info[shdr_info[cnt].shdr.sh_info].idx == 0) {
PRINT("\tSection [%s] links to section [%s], which was "
"marked for removal--it will not be removed.\n",
shdr_info[cnt].name,
shdr_info[shdr_info[cnt].shdr.sh_info].name);
shdr_info[shdr_info[cnt].shdr.sh_info].idx = 1;
changes |= shdr_info[cnt].shdr.sh_info < cnt;
}
/* Mark the section as investigated. */
shdr_info[cnt].idx = 2;
} /* if (shdr_info[cnt].idx == 1) */
} /* for (cnt = 1; cnt < shnum; ++cnt) */
} while (changes);
}
else {
INFO("Not stripping sections.\n");
/* Mark the SHT_NULL section as handled. */
shdr_info[0].idx = 2;
}
/* Mark the section header string table as unused, we will create
a new one as the very last section in the new ELF file.
*/
shdr_info[shstrndx].idx = rebuild_shstrtab ? 0 : 2;
/* We need a string table for the section headers. */
FAILIF_LIBELF((shst = ebl_strtabinit (1 /* null-terminated */)) == NULL,
ebl_strtabinit);
/* Assign new section numbers. */
INFO("Creating new sections...\n");
//shdr_info[0].idx = 0;
for (cnt = idx = 1; cnt < shnum; ++cnt) {
if (shdr_info[cnt].idx > 0) {
shdr_info[cnt].idx = idx++;
/* Create a new section. */
FAILIF_LIBELF((shdr_info[cnt].newscn =
elf_newscn(newelf)) == NULL, elf_newscn);
ASSERT(elf_ndxscn (shdr_info[cnt].newscn) == shdr_info[cnt].idx);
/* Add this name to the section header string table. */
shdr_info[cnt].se = ebl_strtabadd (shst, shdr_info[cnt].name, 0);
INFO("\tsection [%s] (old offset %lld, old size %lld) will have index %d "
"(was %zd).\n",
shdr_info[cnt].name,
shdr_info[cnt].old_shdr.sh_offset,
shdr_info[cnt].old_shdr.sh_size,
shdr_info[cnt].idx,
elf_ndxscn(shdr_info[cnt].scn));
} else {
INFO("\tIgnoring section [%s] (offset %lld, size %lld, index %zd), "
"it will be discarded.\n",
shdr_info[cnt].name,
shdr_info[cnt].shdr.sh_offset,
shdr_info[cnt].shdr.sh_size,
elf_ndxscn(shdr_info[cnt].scn));
}
} /* for */
sections_dropped_or_rearranged = idx != cnt;
Elf_Data *shstrtab_data = NULL;
#if 0
/* Fail if sections are being dropped or rearranged (except for moving shstrtab) or the
symbol filter is not empty, AND the file is an executable.
*/
FAILIF(((idx != cnt && !(cnt - idx == 1 && rebuild_shstrtab)) || sym_filter != NULL) &&
ehdr->e_type != ET_DYN,
"You may not rearrange sections or strip symbols on an executable file!\n");
#endif
INFO("\n\nADJUSTING ELF FILE\n\n");
adjust_elf(elf, elf_name,
newelf, newelf_name,
ebl,
ehdr, /* store ELF header of original library */
sym_filter, num_symbols,
shdr_info, shdr_info_len,
phdr_info,
idx, /* highest_scn_num */
shnum,
shstrndx,
shst,
sections_dropped_or_rearranged,
dynamic_idx, /* index in shdr_info[] of .dynamic section */
dynsym_idx, /* index in shdr_info[] of dynamic symbol table */
shady,
&shstrtab_data,
ehdr->e_type == ET_DYN, /* adjust section ofsets only when the file is a shared library */
rebuild_shstrtab);
/* We have everything from the old file. */
FAILIF_LIBELF(elf_cntl(elf, ELF_C_FDDONE) != 0, elf_cntl);
/* The ELF library better follows our layout when this is not a
relocatable object file. */
elf_flagelf (newelf,
ELF_C_SET,
(ehdr->e_type != ET_REL ? ELF_F_LAYOUT : 0));
/* Finally write the file. */
FAILIF_LIBELF(!dry_run && elf_update(newelf, ELF_C_WRITE) == -1, elf_update);
if (shdr_info != NULL) {
/* For some sections we might have created an table to map symbol
table indices. */
for (cnt = 1; cnt < shdr_info_len; ++cnt) {
FREEIF(shdr_info[cnt].newsymidx);
FREEIF(shdr_info[cnt].symse);
if(shdr_info[cnt].dynsymst != NULL)
ebl_strtabfree (shdr_info[cnt].dynsymst);
}
/* Free the memory. */
FREE (shdr_info);
}
FREEIF(phdr_info);
ebl_closebackend(ebl);
/* Free other resources. */
if (shst != NULL) ebl_strtabfree (shst);
if (shstrtab_data != NULL)
FREEIF(shstrtab_data->d_buf);
}