Add .gnu_hash support
Almost all systems use .gnu_hash so implement it for tcc. For most of them it is the default. tccelf.c: - Add functions elf_gnu_hash/create_gnu_hash/update_gnu_hash - Update new_section/sort_sections/fill_dynamic/tcc_output_elf/elf_output_file Tested with setting .hash section to SHF_PRIVATE in elf_output_file.
This commit is contained in:
herman ten brugge
parent
e5eedc0cda
commit
0fd7376000
1 changed files with 200 additions and 2 deletions
202
tccelf.c
202
tccelf.c
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@ -216,6 +216,7 @@ ST_FUNC Section *new_section(TCCState *s1, const char *name, int sh_type, int sh
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sec->sh_addralign = 2;
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break;
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case SHT_HASH:
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case SHT_GNU_HASH:
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case SHT_REL:
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case SHT_RELA:
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case SHT_DYNSYM:
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@ -373,6 +374,16 @@ static unsigned long elf_hash(const unsigned char *name)
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return h;
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}
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static unsigned long elf_gnu_hash (const unsigned char *name)
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{
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unsigned long h = 5381;
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unsigned char c;
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while ((c = *name++))
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h = h * 33 + c;
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return h;
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}
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/* rebuild hash table of section s */
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/* NOTE: we do factorize the hash table code to go faster */
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static void rebuild_hash(Section *s, unsigned int nb_buckets)
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@ -847,6 +858,186 @@ static void sort_syms(TCCState *s1, Section *s)
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tcc_free(old_to_new_syms);
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}
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/* See: https://flapenguin.me/elf-dt-gnu-hash */
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#define ELFCLASS_BITS (PTR_SIZE * 8)
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static void create_gnu_hash(TCCState *s1)
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{
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int nb_syms, i, ndef, nbuckets, symoffset, bloom_size, bloom_shift;
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ElfW(Sym) *p;
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Section *gnu_hash;
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Section *dynsym = s1->dynsym;
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Elf32_Word *ptr;
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if (dynsym == NULL)
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return;
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gnu_hash = new_section(s1, ".gnu.hash", SHT_GNU_HASH, SHF_ALLOC);
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gnu_hash->link = dynsym->hash->link;
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nb_syms = dynsym->data_offset / sizeof(ElfW(Sym));
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/* count def symbols */
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ndef = 0;
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p = (ElfW(Sym) *)dynsym->data;
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for(i = 0; i < nb_syms; i++, p++)
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ndef += p->st_shndx != SHN_UNDEF;
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/* calculate gnu hash sizes and fill header */
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nbuckets = ndef / 4 + 1;
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symoffset = nb_syms - ndef;
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bloom_shift = PTR_SIZE == 8 ? 6 : 5;
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bloom_size = 1; /* must be power of two */
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while (ndef >= bloom_size * (1 << (bloom_shift - 3)))
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bloom_size *= 2;
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ptr = section_ptr_add(gnu_hash, 4 * 4 +
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PTR_SIZE * bloom_size +
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nbuckets * 4 +
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ndef * 4);
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ptr[0] = nbuckets;
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ptr[1] = symoffset;
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ptr[2] = bloom_size;
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ptr[3] = bloom_shift;
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}
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static void update_gnu_hash(TCCState *s1)
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{
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int *old_to_new_syms;
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ElfW(Sym) *new_syms;
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int nb_syms, i, nbuckets, bloom_size, bloom_shift;
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ElfW(Sym) *p, *q;
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ElfW_Rel *rel;
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Section *sr, *vs;
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Section *gnu_hash;
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Section *dynsym = s1->dynsym;
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int type, sym_index;
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Elf32_Word *ptr, *buckets, *chain, *hash;
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unsigned int *nextbuck;
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addr_t *bloom;
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unsigned char *strtab;
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struct { int first, last; } *buck;
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if (dynsym == NULL)
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return;
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gnu_hash = find_section_create(s1, ".gnu.hash", 0);
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if (gnu_hash == NULL)
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return;
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strtab = dynsym->link->data;
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nb_syms = dynsym->data_offset / sizeof(ElfW(Sym));
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new_syms = tcc_malloc(nb_syms * sizeof(ElfW(Sym)));
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old_to_new_syms = tcc_malloc(nb_syms * sizeof(int));
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hash = tcc_malloc(nb_syms * sizeof(Elf32_Word));
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nextbuck = tcc_malloc(nb_syms * sizeof(int));
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/* calculate hashes and copy undefs */
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p = (ElfW(Sym) *)dynsym->data;
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q = new_syms;
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for(i = 0; i < nb_syms; i++, p++) {
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if (p->st_shndx == SHN_UNDEF) {
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old_to_new_syms[i] = q - new_syms;
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*q++ = *p;
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}
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else
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hash[i] = elf_gnu_hash(strtab + p->st_name);
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}
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ptr = (Elf32_Word *) gnu_hash->data;
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nbuckets = ptr[0];
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bloom_size = ptr[2];
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bloom_shift = ptr[3];
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bloom = (addr_t *) (void *) &ptr[4];
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buckets = (Elf32_Word*) (void *) &bloom[bloom_size];
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chain = &buckets[nbuckets];
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buck = tcc_malloc(nbuckets * sizeof(*buck));
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if (gnu_hash->data_offset != 4 * 4 +
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PTR_SIZE * bloom_size +
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nbuckets * 4 +
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(nb_syms - (q - new_syms)) * 4)
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tcc_error ("gnu_hash size incorrect");
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/* find buckets */
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for(i = 0; i < nbuckets; i++)
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buck[i].first = -1;
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p = (ElfW(Sym) *)dynsym->data;
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for(i = 0; i < nb_syms; i++, p++)
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if (p->st_shndx != SHN_UNDEF) {
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int bucket = hash[i] % nbuckets;
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if (buck[bucket].first == -1)
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buck[bucket].first = buck[bucket].last = i;
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else {
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nextbuck[buck[bucket].last] = i;
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buck[bucket].last = i;
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}
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}
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/* fill buckets/chains/bloom and sort symbols */
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p = (ElfW(Sym) *)dynsym->data;
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for(i = 0; i < nbuckets; i++) {
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int cur = buck[i].first;
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if (cur != -1) {
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buckets[i] = q - new_syms;
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for (;;) {
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old_to_new_syms[cur] = q - new_syms;
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*q++ = p[cur];
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*chain++ = hash[cur] & ~1;
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bloom[(hash[cur] / ELFCLASS_BITS) % bloom_size] |=
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(addr_t)1 << (hash[cur] % ELFCLASS_BITS) |
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(addr_t)1 << ((hash[cur] >> bloom_shift) % ELFCLASS_BITS);
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if (cur == buck[i].last)
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break;
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cur = nextbuck[cur];
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}
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chain[-1] |= 1;
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}
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}
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memcpy(dynsym->data, new_syms, nb_syms * sizeof(ElfW(Sym)));
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tcc_free(new_syms);
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tcc_free(hash);
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tcc_free(buck);
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tcc_free(nextbuck);
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/* modify all the relocations */
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for(i = 1; i < s1->nb_sections; i++) {
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sr = s1->sections[i];
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if (sr->sh_type == SHT_RELX && sr->link == dynsym) {
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for_each_elem(sr, 0, rel, ElfW_Rel) {
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sym_index = ELFW(R_SYM)(rel->r_info);
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type = ELFW(R_TYPE)(rel->r_info);
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sym_index = old_to_new_syms[sym_index];
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rel->r_info = ELFW(R_INFO)(sym_index, type);
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}
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}
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}
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/* modify the versions */
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vs = find_section_create(s1, ".gnu.version", 0);
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if (vs) {
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ElfW(Half) *newver, *versym = (ElfW(Half) *)vs->data;
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if (versym) {
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newver = tcc_malloc(nb_syms * sizeof(*newver));
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for (i = 0; i < nb_syms; i++)
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newver[old_to_new_syms[i]] = versym[i];
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memcpy(vs->data, newver, nb_syms * sizeof(*newver));
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tcc_free(newver);
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}
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}
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tcc_free(old_to_new_syms);
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/* rebuild hash */
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ptr = (Elf32_Word *) dynsym->hash->data;
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rebuild_hash(dynsym, ptr[0]);
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}
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/* relocate symbol table, resolve undefined symbols if do_resolve is
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true and output error if undefined symbol. */
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ST_FUNC void relocate_syms(TCCState *s1, Section *symtab, int do_resolve)
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@ -1912,7 +2103,7 @@ static int sort_sections(TCCState *s1, int *sec_order, Section *interp)
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k = 0x11;
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if (i == nb_sections - 1) /* ".shstrtab" assumed to remain last */
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k = 0xff;
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} else if (s->sh_type == SHT_HASH) {
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} else if (s->sh_type == SHT_HASH || s->sh_type == SHT_GNU_HASH) {
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k = 0x12;
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} else if (s->sh_type == SHT_RELX) {
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k = 0x20;
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@ -2162,7 +2353,12 @@ static void fill_dynamic(TCCState *s1, struct dyn_inf *dyninf)
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Section *s;
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/* put dynamic section entries */
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put_dt(dynamic, DT_HASH, s1->dynsym->hash->sh_addr);
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s = find_section_create (s1, ".hash", 0);
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if (s && s->sh_flags == SHF_ALLOC)
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put_dt(dynamic, DT_HASH, s->sh_addr);
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s = find_section_create (s1, ".gnu.hash", 0);
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if (s && s->sh_flags == SHF_ALLOC)
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put_dt(dynamic, DT_GNU_HASH, s->sh_addr);
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put_dt(dynamic, DT_STRTAB, dyninf->dynstr->sh_addr);
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put_dt(dynamic, DT_SYMTAB, s1->dynsym->sh_addr);
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put_dt(dynamic, DT_STRSZ, dyninf->dynstr->data_offset);
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@ -2335,6 +2531,7 @@ static void tcc_output_elf(TCCState *s1, FILE *f, int phnum, ElfW(Phdr) *phdr,
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offset = sizeof(ElfW(Ehdr)) + phnum * sizeof(ElfW(Phdr));
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sort_syms(s1, symtab_section);
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update_gnu_hash(s1);
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for(i = 1; i < shnum; i++) {
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s = s1->sections[sec_order ? sec_order[i] : i];
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if (s->sh_type != SHT_NOBITS) {
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@ -2615,6 +2812,7 @@ static int elf_output_file(TCCState *s1, const char *filename)
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/* shared library case: simply export all global symbols */
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export_global_syms(s1);
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}
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create_gnu_hash(s1);
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} else {
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build_got_entries(s1, 0);
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}
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