static int init_output_elf()

in contrib/libbpf/src/linker.c [295:438]

• 111 lines of code
• 18 McCabe index (conditional complexity)

static int init_output_elf(struct bpf_linker *linker, const char *file)
{
	int err, str_off;
	Elf64_Sym *init_sym;
	struct dst_sec *sec;

	linker->filename = strdup(file);
	if (!linker->filename)
		return -ENOMEM;

	linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
	if (linker->fd < 0) {
		err = -errno;
		pr_warn("failed to create '%s': %d\n", file, err);
		return err;
	}

	linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
	if (!linker->elf) {
		pr_warn_elf("failed to create ELF object");
		return -EINVAL;
	}

	/* ELF header */
	linker->elf_hdr = elf64_newehdr(linker->elf);
	if (!linker->elf_hdr) {
		pr_warn_elf("failed to create ELF header");
		return -EINVAL;
	}

	linker->elf_hdr->e_machine = EM_BPF;
	linker->elf_hdr->e_type = ET_REL;
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
	linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
	linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
#else
#error "Unknown __BYTE_ORDER__"
#endif

	/* STRTAB */
	/* initialize strset with an empty string to conform to ELF */
	linker->strtab_strs = strset__new(INT_MAX, "", sizeof(""));
	if (libbpf_get_error(linker->strtab_strs))
		return libbpf_get_error(linker->strtab_strs);

	sec = add_dst_sec(linker, ".strtab");
	if (!sec)
		return -ENOMEM;

	sec->scn = elf_newscn(linker->elf);
	if (!sec->scn) {
		pr_warn_elf("failed to create STRTAB section");
		return -EINVAL;
	}

	sec->shdr = elf64_getshdr(sec->scn);
	if (!sec->shdr)
		return -EINVAL;

	sec->data = elf_newdata(sec->scn);
	if (!sec->data) {
		pr_warn_elf("failed to create STRTAB data");
		return -EINVAL;
	}

	str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
	if (str_off < 0)
		return str_off;

	sec->sec_idx = elf_ndxscn(sec->scn);
	linker->elf_hdr->e_shstrndx = sec->sec_idx;
	linker->strtab_sec_idx = sec->sec_idx;

	sec->shdr->sh_name = str_off;
	sec->shdr->sh_type = SHT_STRTAB;
	sec->shdr->sh_flags = SHF_STRINGS;
	sec->shdr->sh_offset = 0;
	sec->shdr->sh_link = 0;
	sec->shdr->sh_info = 0;
	sec->shdr->sh_addralign = 1;
	sec->shdr->sh_size = sec->sec_sz = 0;
	sec->shdr->sh_entsize = 0;

	/* SYMTAB */
	sec = add_dst_sec(linker, ".symtab");
	if (!sec)
		return -ENOMEM;

	sec->scn = elf_newscn(linker->elf);
	if (!sec->scn) {
		pr_warn_elf("failed to create SYMTAB section");
		return -EINVAL;
	}

	sec->shdr = elf64_getshdr(sec->scn);
	if (!sec->shdr)
		return -EINVAL;

	sec->data = elf_newdata(sec->scn);
	if (!sec->data) {
		pr_warn_elf("failed to create SYMTAB data");
		return -EINVAL;
	}

	str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
	if (str_off < 0)
		return str_off;

	sec->sec_idx = elf_ndxscn(sec->scn);
	linker->symtab_sec_idx = sec->sec_idx;

	sec->shdr->sh_name = str_off;
	sec->shdr->sh_type = SHT_SYMTAB;
	sec->shdr->sh_flags = 0;
	sec->shdr->sh_offset = 0;
	sec->shdr->sh_link = linker->strtab_sec_idx;
	/* sh_info should be one greater than the index of the last local
	 * symbol (i.e., binding is STB_LOCAL). But why and who cares?
	 */
	sec->shdr->sh_info = 0;
	sec->shdr->sh_addralign = 8;
	sec->shdr->sh_entsize = sizeof(Elf64_Sym);

	/* .BTF */
	linker->btf = btf__new_empty();
	err = libbpf_get_error(linker->btf);
	if (err)
		return err;

	/* add the special all-zero symbol */
	init_sym = add_new_sym(linker, NULL);
	if (!init_sym)
		return -EINVAL;

	init_sym->st_name = 0;
	init_sym->st_info = 0;
	init_sym->st_other = 0;
	init_sym->st_shndx = SHN_UNDEF;
	init_sym->st_value = 0;
	init_sym->st_size = 0;

	return 0;
}