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https://github.com/frida/tinycc
synced 2024-12-24 22:16:49 +03:00
Generate PLT thumb stub only when necessary
Generate PLT thumb stub for an ARM PLT entry only when at least one Thumb instruction branches to that entry. Warning: To save space, this commit reuses the bit 0 of entries of got_offsets array. The GOT offset is thus saved in a 31 bit value. Make sure to divide by 2 (right shift by 1) an offset before storing it there and conversely to multiply the value by 2 (left shift by 1) before using it.
This commit is contained in:
Thomas Preud'homme
parent
e07802e39d
commit
891dfcdf3f
11
tcc.h
11
tcc.h
@ -33,6 +33,7 @@
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#include <stdlib.h>
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#include <stdio.h>
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#include <limits.h>
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#include <stdarg.h>
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#include <string.h>
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#include <errno.h>
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@ -524,11 +525,15 @@ struct TCCState {
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Section **priv_sections;
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int nb_priv_sections; /* number of private sections */
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/* got handling */
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/* got & plt handling */
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Section *got;
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Section *plt;
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unsigned long *got_offsets;
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int nb_got_offsets;
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struct {
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unsigned long plt_thumb_stub:1;
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/* mult by 2 (or left shift by 1) before use */
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unsigned long got_offset:(sizeof(long)*CHAR_BIT-1);
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} *sym_infos;
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int nb_sym_infos;
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/* give the correspondance from symtab indexes to dynsym indexes */
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int *symtab_to_dynsym;
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76
tccelf.c
76
tccelf.c
@ -581,7 +581,7 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
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break;
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case R_386_GOT32:
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/* we load the got offset */
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*(int *)ptr += s1->got_offsets[sym_index];
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*(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
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break;
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case R_386_16:
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if (s1->output_format != TCC_OUTPUT_FORMAT_BINARY) {
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@ -758,7 +758,7 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
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break;
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case R_ARM_GOT_BREL:
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/* we load the got offset */
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*(int *)ptr += s1->got_offsets[sym_index];
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*(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
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break;
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case R_ARM_COPY:
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break;
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@ -864,14 +864,14 @@ ST_FUNC void relocate_section(TCCState *s1, Section *s)
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}
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#endif
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*(int *)ptr += (s1->got->sh_addr - addr +
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s1->got_offsets[sym_index] - 4);
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(s1->sym_infos[sym_index].got_offset << 1) - 4);
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break;
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case R_X86_64_GOTTPOFF:
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*(int *)ptr += val - s1->got->sh_addr;
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break;
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case R_X86_64_GOT32:
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/* we load the got offset */
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*(int *)ptr += s1->got_offsets[sym_index];
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*(int *)ptr += s1->sym_infos[sym_index].got_offset << 1;
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break;
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#else
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#error unsupported processor
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@ -941,23 +941,36 @@ static int prepare_dynamic_rel(TCCState *s1, Section *sr)
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return count;
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}
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static void put_got_offset(TCCState *s1, int index, unsigned long val)
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static void put_sym_info(TCCState *s1, int index)
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{
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int n;
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unsigned long *tab;
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typeof(s1->sym_infos) tab;
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if (index >= s1->nb_got_offsets) {
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if (index >= s1->nb_sym_infos) {
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/* find immediately bigger power of 2 and reallocate array */
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n = 1;
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while (index >= n)
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n *= 2;
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tab = tcc_realloc(s1->got_offsets, n * sizeof(unsigned long));
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s1->got_offsets = tab;
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memset(s1->got_offsets + s1->nb_got_offsets, 0,
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(n - s1->nb_got_offsets) * sizeof(unsigned long));
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s1->nb_got_offsets = n;
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tab = tcc_realloc(s1->sym_infos, n * sizeof(unsigned long));
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s1->sym_infos = tab;
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memset(s1->sym_infos + s1->nb_sym_infos, 0,
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(n - s1->nb_sym_infos) * sizeof(unsigned long));
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s1->nb_sym_infos = n;
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}
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s1->got_offsets[index] = val;
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}
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#ifdef TCC_TARGET_ARM
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static void put_plt_thumb_stub(TCCState *s1, int index, unsigned char bit)
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{
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put_sym_info(s1, index);
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s1->sym_infos[index].plt_thumb_stub = bit;
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}
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#endif
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static void put_got_offset(TCCState *s1, int index, unsigned long val)
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{
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put_sym_info(s1, index);
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s1->sym_infos[index].got_offset = val >> 1;
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}
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/* XXX: suppress that */
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@ -1021,8 +1034,8 @@ static void put_got_entry(TCCState *s1,
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build_got(s1);
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/* if a got entry already exists for that symbol, no need to add one */
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if (sym_index < s1->nb_got_offsets &&
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s1->got_offsets[sym_index] != 0)
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if (sym_index < s1->nb_sym_infos &&
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s1->sym_infos[sym_index].got_offset << 1)
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return;
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put_got_offset(s1, sym_index, s1->got->data_offset);
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@ -1102,10 +1115,13 @@ static void put_got_entry(TCCState *s1,
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put32(p + 12, 0xe5bef008);
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}
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p = section_ptr_add(plt, 20);
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put32(p , 0x4778); // bx pc
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put32(p+2, 0x46c0); // nop
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p += 4;
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if (s1->sym_infos[sym_index].plt_thumb_stub) {
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p = section_ptr_add(plt, 20);
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put32(p , 0x4778); // bx pc
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put32(p+2, 0x46c0); // nop
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p += 4;
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} else
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p = section_ptr_add(plt, 16);
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put32(p , 0xe59fc004); // ldr ip, [pc, #4] // offset in GOT
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put32(p+4, 0xe08fc00c); // add ip, pc, ip // absolute address or offset
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put32(p+8, 0xe59cf000); // ldr pc, [ip] // load absolute address or load offset
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@ -1492,9 +1508,9 @@ ST_FUNC void fill_got_entry(TCCState *s1, ElfW_Rel *rel)
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ElfW(Sym) *sym = &((ElfW(Sym) *) symtab_section->data)[sym_index];
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unsigned long offset;
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if (sym_index >= s1->nb_got_offsets)
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if (sym_index >= s1->nb_sym_infos)
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return;
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offset = s1->got_offsets[sym_index];
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offset = s1->sym_infos[sym_index].got_offset << 1;
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section_reserve(s1->got, offset + PTR_SIZE);
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#ifdef TCC_TARGET_X86_64
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/* only works for x86-64 */
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@ -2068,7 +2084,8 @@ static int elf_output_file(TCCState *s1, const char *filename)
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x=s1->got->sh_addr - s1->plt->sh_addr - 12;
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p += 16;
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while (p < p_end) {
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p += 4;
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if (get32(p) == 0x46c04778) /* PLT Thumb stub present */
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p += 4;
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put32(p + 12, x + get32(p + 12) + s1->plt->data - p);
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p += 16;
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}
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@ -2302,7 +2319,7 @@ static int elf_output_file(TCCState *s1, const char *filename)
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tcc_free(s1->symtab_to_dynsym);
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tcc_free(section_order);
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tcc_free(phdr);
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tcc_free(s1->got_offsets);
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tcc_free(s1->sym_infos);
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return ret;
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}
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@ -2597,6 +2614,19 @@ ST_FUNC int tcc_load_object_file(TCCState *s1,
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rel->r_info = ELFW(R_INFO)(sym_index, type);
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/* offset the relocation offset */
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rel->r_offset += offseti;
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#ifdef TCC_TARGET_ARM
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/* Jumps and branches from a Thumb code to a PLT entry need
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special handling since PLT entries are ARM code.
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Unconditional bl instructions referencing PLT entries are
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handled by converting these instructions into blx
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instructions. Other case of instructions referencing a PLT
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entry require to add a Thumb stub before the PLT entry to
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switch to ARM mode. We set bit 0 of the got offset of a
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symbol to indicate such a case. */
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if (type == R_ARM_THM_JUMP24) {
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put_plt_thumb_stub(s1, sym_index, 1);
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}
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#endif
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}
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break;
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default:
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