Tentative rewrite of Dareog to write DWARF to ELF
Rewrite from Simon Ser's code from Dareog. Yet untested.
This commit is contained in:
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2 changed files with 500 additions and 0 deletions
446
DwarfSynth/c_bindings/dwarf_write.c
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446
DwarfSynth/c_bindings/dwarf_write.c
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/** dwarf_write -- set of functions to add a given DWARF table to an ELF file
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*
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* Mostly based on work by emersion on Dareog
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* <https://github.com/emersion/dareog>
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*/
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#include "dwarf_write.h"
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struct internal_state {
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Elf *elf;
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};
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static Elf_Scn *find_section_by_name(Elf *elf, const char *section_name) {
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size_t sections_num;
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if (elf_getshdrnum(elf, §ions_num)) {
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return NULL;
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}
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size_t shstrndx;
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if (elf_getshdrstrndx(elf, &shstrndx)) {
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return NULL;
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}
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for (size_t i = 0; i < sections_num; ++i) {
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Elf_Scn *s = elf_getscn(elf, i);
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if (s == NULL) {
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return NULL;
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}
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GElf_Shdr sh;
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if (!gelf_getshdr(s, &sh)) {
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return NULL;
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}
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char *name = elf_strptr(elf, shstrndx, sh.sh_name);
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if (name == NULL) {
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return NULL;
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}
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if (strcmp(name, section_name) == 0) {
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return s;
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}
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}
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return NULL;
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}
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static Elf_Scn *create_section(Elf *elf, const char *name) {
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Elf_Scn *scn = elf_newscn(elf);
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if (scn == NULL) {
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fprintf(stderr, "elf_newscn() failed: %s\n", elf_errmsg(-1));
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return NULL;
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}
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GElf_Shdr shdr;
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if (!gelf_getshdr(scn, &shdr)) {
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fprintf(stderr, "gelf_getshdr() failed\n");
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return NULL;
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}
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// Add section name to .shstrtab
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Elf_Scn *shstrtab = find_section_by_name(elf, ".shstrtab");
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if (shstrtab == NULL) {
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fprintf(stderr, "can't find .shstrtab section\n");
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return NULL;
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}
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GElf_Shdr shstrtab_shdr;
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if (!gelf_getshdr(shstrtab, &shstrtab_shdr)) {
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fprintf(stderr, "gelf_getshdr(shstrtab) failed\n");
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return NULL;
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}
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Elf_Data *shstrtab_data = elf_newdata(shstrtab);
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if (shstrtab_data == NULL) {
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fprintf(stderr, "elf_newdata(shstrtab) failed\n");
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return NULL;
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}
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shstrtab_data->d_buf = strdup(name);
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shstrtab_data->d_size = strlen(name) + 1;
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shstrtab_data->d_align = 1;
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shdr.sh_name = shstrtab_shdr.sh_size;
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shstrtab_shdr.sh_size += shstrtab_data->d_size;
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if (!gelf_update_shdr(scn, &shdr)) {
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fprintf(stderr, "gelf_update_shdr() failed\n");
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return NULL;
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}
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if (!gelf_update_shdr(shstrtab, &shstrtab_shdr)) {
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fprintf(stderr, "gelf_update_shdr(shstrtab) failed\n");
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return NULL;
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}
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return scn;
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}
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static int find_section_symbol(Elf *elf, size_t index, GElf_Sym *sym) {
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Elf_Scn *symtab = find_section_by_name(elf, ".symtab");
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if (symtab == NULL) {
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fprintf(stderr, "can't find .symtab section\n");
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return -1;
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}
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Elf_Data *symtab_data = elf_getdata(symtab, NULL);
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if (symtab_data == NULL) {
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fprintf(stderr, "elf_getdata(symtab) failed\n");
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return -1;
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}
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GElf_Shdr symtab_shdr;
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if (!gelf_getshdr(symtab, &symtab_shdr)) {
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fprintf(stderr, "gelf_getshdr(symtab) failed\n");
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return -1;
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}
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int symbols_nr = symtab_shdr.sh_size / symtab_shdr.sh_entsize;
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for (int i = 0; i < symbols_nr; ++i) {
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if (!gelf_getsym(symtab_data, i, sym)) {
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fprintf(stderr, "gelf_getsym() failed\n");
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continue;
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}
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if (GELF_ST_TYPE(sym->st_info) == STT_SECTION &&
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index == sym->st_shndx) {
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return i;
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}
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}
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return -1;
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}
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static Elf_Scn *create_debug_frame_section(Elf *elf, const char *name,
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char *buf, size_t len) {
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Elf_Scn *scn = create_section(elf, name);
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if (scn == NULL) {
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return NULL;
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}
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Elf_Data *data = elf_newdata(scn);
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if (data == NULL) {
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fprintf(stderr, "elf_newdata() failed: %s\n", elf_errmsg(-1));
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return NULL;
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}
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data->d_align = 4;
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data->d_buf = buf;
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data->d_size = len;
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GElf_Shdr shdr;
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if (!gelf_getshdr(scn, &shdr)) {
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fprintf(stderr, "gelf_getshdr() failed\n");
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return NULL;
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}
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shdr.sh_size = len;
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shdr.sh_type = SHT_PROGBITS;
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shdr.sh_addralign = 1;
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shdr.sh_flags = SHF_ALLOC;
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if (!gelf_update_shdr(scn, &shdr)) {
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fprintf(stderr, "gelf_update_shdr() failed\n");
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return NULL;
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}
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return scn;
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}
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static Elf_Scn *create_rela_section(Elf *elf, const char *name, Elf_Scn *base,
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char *buf, size_t len) {
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Elf_Scn *scn = create_section(elf, name);
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if (scn == NULL) {
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fprintf(stderr, "can't create rela section\n");
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return NULL;
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}
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Elf_Data *data = elf_newdata(scn);
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if (!data) {
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fprintf(stderr, "elf_newdata() failed\n");
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return NULL;
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}
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data->d_buf = buf;
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data->d_size = len;
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data->d_align = 1;
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Elf_Scn *symtab = find_section_by_name(elf, ".symtab");
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if (symtab == NULL) {
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fprintf(stderr, "can't find .symtab section\n");
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return NULL;
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}
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GElf_Shdr shdr;
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if (!gelf_getshdr(scn, &shdr)) {
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fprintf(stderr, "gelf_getshdr() failed\n");
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return NULL;
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}
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shdr.sh_size = data->d_size;
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shdr.sh_type = SHT_RELA;
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shdr.sh_addralign = 8;
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shdr.sh_link = elf_ndxscn(symtab);
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shdr.sh_info = elf_ndxscn(base);
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shdr.sh_flags = SHF_INFO_LINK;
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if (!gelf_update_shdr(scn, &shdr)) {
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fprintf(stderr, "gelf_update_shdr() failed\n");
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return NULL;
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}
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return scn;
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}
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static int write_fde_instruction(struct dwarfw_fde *fde,
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struct pre_dwarf_entry *cur_entry, FILE *f) {
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reg_t reg = cur_entry->cfa_offset_reg;
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if (reg == DW_REG_INV) {
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fprintf(stderr, "warning: dwarf_write: undefined CFA at "
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"0x%" PRIxPTR "\n",
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cur_entry->location);
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// write an undefined ra
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dwarfw_cie_write_undefined(fde->cie, 16, f);
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} else if (reg <= DW_MAX_REG) {
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dwarfw_cie_write_def_cfa(fde->cie, reg, cur_entry->cfa_offset, f);
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// ra's offset is fixed at -8
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dwarfw_cie_write_offset(fde->cie, 16, -8, f);
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} else {
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fprintf(stderr,
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"error: dwarf_write: unsupported register %d at 0x%" PRIxPTR
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" as CFA offset\n",
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reg, cur_entry->location);
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return -1;
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}
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return 0;
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}
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static int write_all_fde_instructions(struct dwarfw_fde *fde,
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struct pre_dwarf_fde *cur_source, FILE *f)
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{
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for (size_t entry_id = 0; entry_id < cur_source->num; entry_id++) {
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int rv = write_fde_instruction(
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fde, &(cur_source->entries[entry_id]), f);
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if(rv != 0) {
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return -1;
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}
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if(entry_id != cur_source->num - 1) { // Not the last row
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addr_t loc_delta =
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cur_source->entries[entry_id + 1].location
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- cur_source->entries[entry_id].location;
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dwarfw_cie_write_advance_loc(fde->cie, loc_delta, f);
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}
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}
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return 0;
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}
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static int process_section(struct internal_state* state,
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struct pre_dwarf* pre_dwarf, Elf_Scn *s, FILE *f, size_t *written,
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FILE *rela_f)
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{
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size_t shndx = elf_ndxscn(s);
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GElf_Sym text_sym;
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int text_sym_idx = find_section_symbol(state->elf, shndx, &text_sym);
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if (text_sym_idx < 0) {
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fprintf(stderr, "can't find .text section in symbol table\n");
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return 1;
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}
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struct dwarfw_cie cie = {
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.version = 1,
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.augmentation = "zR",
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.code_alignment = 1,
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.data_alignment = -8,
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.return_address_register = 16,
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.augmentation_data = {
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.pointer_encoding = DW_EH_PE_sdata4 | DW_EH_PE_pcrel,
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},
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};
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size_t n;
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if (!(n = dwarfw_cie_write(&cie, f))) {
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fprintf(stderr, "dwarfw_cie_write() failed\n");
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return -1;
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}
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*written += n;
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// Generate the FDEs
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for (size_t fde_id = 0; fde_id < pre_dwarf->num_fde; ++fde_id) {
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struct pre_dwarf_fde* cur_fde = &(pre_dwarf->fdes[fde_id]);
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struct dwarfw_fde fde = {
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.cie = &cie,
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.initial_location = cur_fde->initial_location,
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};
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char *instr_buf;
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size_t instr_len;
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FILE *instr_f = open_memstream(&instr_buf, &instr_len);
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if (instr_f == NULL) {
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fprintf(stderr, "open_memstream() failed\n");
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return -1;
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}
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if (write_all_fde_instructions(&fde, cur_fde, instr_f)) {
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fprintf(stderr, "write_all_fde_instructions() failed\n");
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return -1;
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}
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fclose(instr_f);
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if (instr_len == 0) {
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continue;
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}
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fde.address_range = cur_fde->end_location - cur_fde->initial_location;
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fde.instructions_length = instr_len;
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fde.instructions = instr_buf;
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fde.cie_pointer = *written;
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GElf_Rela initial_position_rela;
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if (!(n = dwarfw_fde_write(&fde, &initial_position_rela, f))) {
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fprintf(stderr, "dwarfw_fde_write() failed\n");
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return -1;
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}
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initial_position_rela.r_offset += *written;
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*written += n;
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free(instr_buf);
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// r_offset and r_addend have already been populated by dwarfw_fde_write
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initial_position_rela.r_info = GELF_R_INFO(text_sym_idx,
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ELF32_R_TYPE(initial_position_rela.r_info));
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if (!fwrite(&initial_position_rela, 1, sizeof(GElf_Rela), rela_f)) {
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fprintf(stderr, "can't write rela\n");
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return 1;
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}
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}
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return 0;
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}
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int write_dwarf(char* objname, struct pre_dwarf* pre_dwarf) {
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elf_version(EV_CURRENT);
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int fd = open(objname, O_RDWR);
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if (fd == -1) {
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fprintf(stderr, "cannot open file\n");
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return -1;
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}
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Elf *elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
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if (!elf) {
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fprintf(stderr, "elf_begin() failed\n");
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return -1;
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}
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// Check the ELF object
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Elf_Kind ek = elf_kind(elf);
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if (ek != ELF_K_ELF) {
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fprintf(stderr, "not an ELF object\n");
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return 1;
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}
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size_t sections_num;
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if (elf_getshdrnum(elf, §ions_num)) {
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return 1;
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}
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size_t shstrtab_idx;
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if (elf_getshdrstrndx(elf, &shstrtab_idx)) {
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fprintf(stderr, "elf_getshdrstrndx() failed\n");
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return -1;
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}
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struct internal_state state = { .elf = elf };
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char *buf;
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size_t len;
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FILE *f = open_memstream(&buf, &len);
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if (f == NULL) {
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fprintf(stderr, "open_memstream() failed\n");
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return 1;
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}
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char *rela_buf;
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size_t rela_len;
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FILE *rela_f = open_memstream(&rela_buf, &rela_len);
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if (rela_f == NULL) {
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fprintf(stderr, "open_memstream() failed\n");
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return 1;
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}
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size_t written = 0;
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for (size_t i = 0; i < sections_num; ++i) {
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Elf_Scn *s = elf_getscn(elf, i);
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if (s == NULL) {
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return 1;
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}
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GElf_Shdr sh;
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if (!gelf_getshdr(s, &sh)) {
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return 1;
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}
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if ((sh.sh_flags & SHF_EXECINSTR) == 0) {
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continue;
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}
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if (process_section(&state, pre_dwarf, s, f, &written, rela_f)) {
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return 1;
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}
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}
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fclose(f);
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fclose(rela_f);
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// Create the .eh_frame section
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Elf_Scn *scn = create_debug_frame_section(elf, ".eh_frame", buf, len);
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if (scn == NULL) {
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fprintf(stderr, "create_debug_frame_section() failed\n");
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return 1;
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}
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// Create the .eh_frame.rela section
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Elf_Scn *rela = create_rela_section(elf, ".rela.eh_frame", scn,
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rela_buf, rela_len);
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if (rela == NULL) {
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fprintf(stderr, "create_rela_section() failed\n");
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return 1;
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}
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// Write the modified ELF object
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elf_flagelf(elf, ELF_C_SET, ELF_F_DIRTY);
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if (elf_update(elf, ELF_C_WRITE) < 0) {
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fprintf(stderr, "elf_update() failed: %s\n", elf_errmsg(-1));
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return 1;
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}
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free(buf);
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free(rela_buf);
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elf_end(elf);
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close(fd);
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return 0;
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}
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54
DwarfSynth/c_bindings/dwarf_write.h
Normal file
54
DwarfSynth/c_bindings/dwarf_write.h
Normal file
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@ -0,0 +1,54 @@
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/** dwarf_write -- set of functions to add a given DWARF table to an ELF file
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*
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* Mostly based on work by emersion on Dareog
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* <https://github.com/emersion/dareog>
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*/
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#pragma once
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#include "../../libdwarfw/include/dwarfw.h"
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#include <dwarf.h>
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#include <gelf.h>
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#include <string.h>
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#include <stdint.h>
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#include <inttypes.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <libelf.h>
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#include <limits.h>
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#include <stddef.h>
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typedef uint8_t reg_t;
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typedef long long int offset_t;
|
||||
typedef uintptr_t addr_t;
|
||||
|
||||
|
||||
// ====== Registers definition for x86_64 ======
|
||||
#define DW_REG_RA ((reg_t)16)
|
||||
#define DW_REG_RBP ((reg_t)6)
|
||||
#define DW_REG_RSP ((reg_t)7)
|
||||
#define DW_REG_INV ((reg_t)0xff)
|
||||
|
||||
#define DW_MAX_REG ((reg_t)31)
|
||||
|
||||
/// Very basic DWARF structure representing only CFA -- RA is at fixed offset
|
||||
struct pre_dwarf_entry {
|
||||
addr_t location;
|
||||
reg_t cfa_offset_reg;
|
||||
offset_t cfa_offset;
|
||||
};
|
||||
|
||||
struct pre_dwarf_fde {
|
||||
size_t num;
|
||||
struct pre_dwarf_entry* entries;
|
||||
|
||||
addr_t initial_location, end_location;
|
||||
};
|
||||
|
||||
struct pre_dwarf {
|
||||
size_t num_fde;
|
||||
struct pre_dwarf_fde* fdes;
|
||||
};
|
||||
Loading…
Reference in a new issue