// SPDX-License-Identifier: GPL-2.0-or-later /* * elf.c - ELF access library * * Adapted from kpatch (https://github.com/dynup/kpatch): * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com> * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> */ #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <errno.h> #include "builtin.h" #include "elf.h" #include "warn.h" #define MAX_NAME_LEN 128 static inline u32 str_hash(const char *str) { return jhash(str, strlen(str), 0); } static inline int elf_hash_bits(void) { return vmlinux ? ELF_HASH_BITS : 16; } #define elf_hash_add(hashtable, node, key) \ hlist_add_head(node, &hashtable[hash_min(key, elf_hash_bits())]) static void elf_hash_init(struct hlist_head *table) { __hash_init(table, 1U << elf_hash_bits()); } #define elf_hash_for_each_possible(name, obj, member, key) \ hlist_for_each_entry(obj, &name[hash_min(key, elf_hash_bits())], member) static void rb_add(struct rb_root *tree, struct rb_node *node, int (*cmp)(struct rb_node *, const struct rb_node *)) { struct rb_node **link = &tree->rb_node; struct rb_node *parent = NULL; while (*link) { parent = *link; if (cmp(node, parent) < 0) link = &parent->rb_left; else link = &parent->rb_right; } rb_link_node(node, parent, link); rb_insert_color(node, tree); } static struct rb_node *rb_find_first(const struct rb_root *tree, const void *key, int (*cmp)(const void *key, const struct rb_node *)) { struct rb_node *node = tree->rb_node; struct rb_node *match = NULL; while (node) { int c = cmp(key, node); if (c <= 0) { if (!c) match = node; node = node->rb_left; } else if (c > 0) { node = node->rb_right; } } return match; } static struct rb_node *rb_next_match(struct rb_node *node, const void *key, int (*cmp)(const void *key, const struct rb_node *)) { node = rb_next(node); if (node && cmp(key, node)) node = NULL; return node; } #define rb_for_each(tree, node, key, cmp) \ for ((node) = rb_find_first((tree), (key), (cmp)); \ (node); (node) = rb_next_match((node), (key), (cmp))) static int symbol_to_offset(struct rb_node *a, const struct rb_node *b) { struct symbol *sa = rb_entry(a, struct symbol, node); struct symbol *sb = rb_entry(b, struct symbol, node); if (sa->offset < sb->offset) return -1; if (sa->offset > sb->offset) return 1; if (sa->len < sb->len) return -1; if (sa->len > sb->len) return 1; sa->alias = sb; return 0; } static int symbol_by_offset(const void *key, const struct rb_node *node) { const struct symbol *s = rb_entry(node, struct symbol, node); const unsigned long *o = key; if (*o < s->offset) return -1; if (*o >= s->offset + s->len) return 1; return 0; } struct section *find_section_by_name(const struct elf *elf, const char *name) { struct section *sec; elf_hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name)) if (!strcmp(sec->name, name)) return sec; return NULL; } static struct section *find_section_by_index(struct elf *elf, unsigned int idx) { struct section *sec; elf_hash_for_each_possible(elf->section_hash, sec, hash, idx) if (sec->idx == idx) return sec; return NULL; } static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) { struct symbol *sym; elf_hash_for_each_possible(elf->symbol_hash, sym, hash, idx) if (sym->idx == idx) return sym; return NULL; } struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) { struct rb_node *node; rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) { struct symbol *s = rb_entry(node, struct symbol, node); if (s->offset == offset && s->type != STT_SECTION) return s; } return NULL; } struct symbol *find_func_by_offset(struct section *sec, unsigned long offset) { struct rb_node *node; rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) { struct symbol *s = rb_entry(node, struct symbol, node); if (s->offset == offset && s->type == STT_FUNC) return s; } return NULL; } struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset) { struct rb_node *node; rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) { struct symbol *s = rb_entry(node, struct symbol, node); if (s->type != STT_SECTION) return s; } return NULL; } struct symbol *find_func_containing(struct section *sec, unsigned long offset) { struct rb_node *node; rb_for_each(&sec->symbol_tree, node, &offset, symbol_by_offset) { struct symbol *s = rb_entry(node, struct symbol, node); if (s->type == STT_FUNC) return s; } return NULL; } struct symbol *find_symbol_by_name(const struct elf *elf, const char *name) { struct symbol *sym; elf_hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name)) if (!strcmp(sym->name, name)) return sym; return NULL; } struct rela *find_rela_by_dest_range(const struct elf *elf, struct section *sec, unsigned long offset, unsigned int len) { struct rela *rela, *r = NULL; unsigned long o; if (!sec->rela) return NULL; sec = sec->rela; for_offset_range(o, offset, offset + len) { elf_hash_for_each_possible(elf->rela_hash, rela, hash, sec_offset_hash(sec, o)) { if (rela->sec != sec) continue; if (rela->offset >= offset && rela->offset < offset + len) { if (!r || rela->offset < r->offset) r = rela; } } if (r) return r; } return NULL; } struct rela *find_rela_by_dest(const struct elf *elf, struct section *sec, unsigned long offset) { return find_rela_by_dest_range(elf, sec, offset, 1); } static int read_sections(struct elf *elf) { Elf_Scn *s = NULL; struct section *sec; size_t shstrndx, sections_nr; int i; if (elf_getshdrnum(elf->elf, §ions_nr)) { WARN_ELF("elf_getshdrnum"); return -1; } if (elf_getshdrstrndx(elf->elf, &shstrndx)) { WARN_ELF("elf_getshdrstrndx"); return -1; } for (i = 0; i < sections_nr; i++) { sec = malloc(sizeof(*sec)); if (!sec) { perror("malloc"); return -1; } memset(sec, 0, sizeof(*sec)); INIT_LIST_HEAD(&sec->symbol_list); INIT_LIST_HEAD(&sec->rela_list); s = elf_getscn(elf->elf, i); if (!s) { WARN_ELF("elf_getscn"); return -1; } sec->idx = elf_ndxscn(s); if (!gelf_getshdr(s, &sec->sh)) { WARN_ELF("gelf_getshdr"); return -1; } sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); if (!sec->name) { WARN_ELF("elf_strptr"); return -1; } if (sec->sh.sh_size != 0) { sec->data = elf_getdata(s, NULL); if (!sec->data) { WARN_ELF("elf_getdata"); return -1; } if (sec->data->d_off != 0 || sec->data->d_size != sec->sh.sh_size) { WARN("unexpected data attributes for %s", sec->name); return -1; } } sec->len = sec->sh.sh_size; list_add_tail(&sec->list, &elf->sections); elf_hash_add(elf->section_hash, &sec->hash, sec->idx); elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); } if (stats) printf("nr_sections: %lu\n", (unsigned long)sections_nr); /* sanity check, one more call to elf_nextscn() should return NULL */ if (elf_nextscn(elf->elf, s)) { WARN("section entry mismatch"); return -1; } return 0; } static int read_symbols(struct elf *elf) { struct section *symtab, *symtab_shndx, *sec; struct symbol *sym, *pfunc; struct list_head *entry; struct rb_node *pnode; int symbols_nr, i; char *coldstr; Elf_Data *shndx_data = NULL; Elf32_Word shndx; symtab = find_section_by_name(elf, ".symtab"); if (!symtab) { WARN("missing symbol table"); return -1; } symtab_shndx = find_section_by_name(elf, ".symtab_shndx"); if (symtab_shndx) shndx_data = symtab_shndx->data; symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; for (i = 0; i < symbols_nr; i++) { sym = malloc(sizeof(*sym)); if (!sym) { perror("malloc"); return -1; } memset(sym, 0, sizeof(*sym)); sym->alias = sym; sym->idx = i; if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym, &shndx)) { WARN_ELF("gelf_getsymshndx"); goto err; } sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, sym->sym.st_name); if (!sym->name) { WARN_ELF("elf_strptr"); goto err; } sym->type = GELF_ST_TYPE(sym->sym.st_info); sym->bind = GELF_ST_BIND(sym->sym.st_info); if ((sym->sym.st_shndx > SHN_UNDEF && sym->sym.st_shndx < SHN_LORESERVE) || (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) { if (sym->sym.st_shndx != SHN_XINDEX) shndx = sym->sym.st_shndx; sym->sec = find_section_by_index(elf, shndx); if (!sym->sec) { WARN("couldn't find section for symbol %s", sym->name); goto err; } if (sym->type == STT_SECTION) { sym->name = sym->sec->name; sym->sec->sym = sym; } } else sym->sec = find_section_by_index(elf, 0); sym->offset = sym->sym.st_value; sym->len = sym->sym.st_size; rb_add(&sym->sec->symbol_tree, &sym->node, symbol_to_offset); pnode = rb_prev(&sym->node); if (pnode) entry = &rb_entry(pnode, struct symbol, node)->list; else entry = &sym->sec->symbol_list; list_add(&sym->list, entry); elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx); elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name)); } if (stats) printf("nr_symbols: %lu\n", (unsigned long)symbols_nr); /* Create parent/child links for any cold subfunctions */ list_for_each_entry(sec, &elf->sections, list) { list_for_each_entry(sym, &sec->symbol_list, list) { char pname[MAX_NAME_LEN + 1]; size_t pnamelen; if (sym->type != STT_FUNC) continue; sym->pfunc = sym->cfunc = sym; coldstr = strstr(sym->name, ".cold"); if (!coldstr) continue; pnamelen = coldstr - sym->name; if (pnamelen > MAX_NAME_LEN) { WARN("%s(): parent function name exceeds maximum length of %d characters", sym->name, MAX_NAME_LEN); return -1; } strncpy(pname, sym->name, pnamelen); pname[pnamelen] = '\0'; pfunc = find_symbol_by_name(elf, pname); if (!pfunc) { WARN("%s(): can't find parent function", sym->name); return -1; } sym->pfunc = pfunc; pfunc->cfunc = sym; /* * Unfortunately, -fnoreorder-functions puts the child * inside the parent. Remove the overlap so we can * have sane assumptions. * * Note that pfunc->len now no longer matches * pfunc->sym.st_size. */ if (sym->sec == pfunc->sec && sym->offset >= pfunc->offset && sym->offset + sym->len == pfunc->offset + pfunc->len) { pfunc->len -= sym->len; } } } return 0; err: free(sym); return -1; } void elf_add_rela(struct elf *elf, struct rela *rela) { struct section *sec = rela->sec; list_add_tail(&rela->list, &sec->rela_list); elf_hash_add(elf->rela_hash, &rela->hash, rela_hash(rela)); } static int read_relas(struct elf *elf) { struct section *sec; struct rela *rela; int i; unsigned int symndx; unsigned long nr_rela, max_rela = 0, tot_rela = 0; list_for_each_entry(sec, &elf->sections, list) { if (sec->sh.sh_type != SHT_RELA) continue; sec->base = find_section_by_name(elf, sec->name + 5); if (!sec->base) { WARN("can't find base section for rela section %s", sec->name); return -1; } sec->base->rela = sec; nr_rela = 0; for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { rela = malloc(sizeof(*rela)); if (!rela) { perror("malloc"); return -1; } memset(rela, 0, sizeof(*rela)); if (!gelf_getrela(sec->data, i, &rela->rela)) { WARN_ELF("gelf_getrela"); return -1; } rela->type = GELF_R_TYPE(rela->rela.r_info); rela->addend = rela->rela.r_addend; rela->offset = rela->rela.r_offset; symndx = GELF_R_SYM(rela->rela.r_info); rela->sym = find_symbol_by_index(elf, symndx); rela->sec = sec; if (!rela->sym) { WARN("can't find rela entry symbol %d for %s", symndx, sec->name); return -1; } elf_add_rela(elf, rela); nr_rela++; } max_rela = max(max_rela, nr_rela); tot_rela += nr_rela; } if (stats) { printf("max_rela: %lu\n", max_rela); printf("tot_rela: %lu\n", tot_rela); } return 0; } struct elf *elf_open_read(const char *name, int flags) { struct elf *elf; Elf_Cmd cmd; elf_version(EV_CURRENT); elf = malloc(sizeof(*elf)); if (!elf) { perror("malloc"); return NULL; } memset(elf, 0, offsetof(struct elf, sections)); INIT_LIST_HEAD(&elf->sections); elf_hash_init(elf->symbol_hash); elf_hash_init(elf->symbol_name_hash); elf_hash_init(elf->section_hash); elf_hash_init(elf->section_name_hash); elf_hash_init(elf->rela_hash); elf->fd = open(name, flags); if (elf->fd == -1) { fprintf(stderr, "objtool: Can't open '%s': %s\n", name, strerror(errno)); goto err; } if ((flags & O_ACCMODE) == O_RDONLY) cmd = ELF_C_READ_MMAP; else if ((flags & O_ACCMODE) == O_RDWR) cmd = ELF_C_RDWR; else /* O_WRONLY */ cmd = ELF_C_WRITE; elf->elf = elf_begin(elf->fd, cmd, NULL); if (!elf->elf) { WARN_ELF("elf_begin"); goto err; } if (!gelf_getehdr(elf->elf, &elf->ehdr)) { WARN_ELF("gelf_getehdr"); goto err; } if (read_sections(elf)) goto err; if (read_symbols(elf)) goto err; if (read_relas(elf)) goto err; return elf; err: elf_close(elf); return NULL; } struct section *elf_create_section(struct elf *elf, const char *name, size_t entsize, int nr) { struct section *sec, *shstrtab; size_t size = entsize * nr; Elf_Scn *s; Elf_Data *data; sec = malloc(sizeof(*sec)); if (!sec) { perror("malloc"); return NULL; } memset(sec, 0, sizeof(*sec)); INIT_LIST_HEAD(&sec->symbol_list); INIT_LIST_HEAD(&sec->rela_list); s = elf_newscn(elf->elf); if (!s) { WARN_ELF("elf_newscn"); return NULL; } sec->name = strdup(name); if (!sec->name) { perror("strdup"); return NULL; } sec->idx = elf_ndxscn(s); sec->len = size; sec->changed = true; sec->data = elf_newdata(s); if (!sec->data) { WARN_ELF("elf_newdata"); return NULL; } sec->data->d_size = size; sec->data->d_align = 1; if (size) { sec->data->d_buf = malloc(size); if (!sec->data->d_buf) { perror("malloc"); return NULL; } memset(sec->data->d_buf, 0, size); } if (!gelf_getshdr(s, &sec->sh)) { WARN_ELF("gelf_getshdr"); return NULL; } sec->sh.sh_size = size; sec->sh.sh_entsize = entsize; sec->sh.sh_type = SHT_PROGBITS; sec->sh.sh_addralign = 1; sec->sh.sh_flags = SHF_ALLOC; /* Add section name to .shstrtab (or .strtab for Clang) */ shstrtab = find_section_by_name(elf, ".shstrtab"); if (!shstrtab) shstrtab = find_section_by_name(elf, ".strtab"); if (!shstrtab) { WARN("can't find .shstrtab or .strtab section"); return NULL; } s = elf_getscn(elf->elf, shstrtab->idx); if (!s) { WARN_ELF("elf_getscn"); return NULL; } data = elf_newdata(s); if (!data) { WARN_ELF("elf_newdata"); return NULL; } data->d_buf = sec->name; data->d_size = strlen(name) + 1; data->d_align = 1; sec->sh.sh_name = shstrtab->len; shstrtab->len += strlen(name) + 1; shstrtab->changed = true; list_add_tail(&sec->list, &elf->sections); elf_hash_add(elf->section_hash, &sec->hash, sec->idx); elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); return sec; } struct section *elf_create_rela_section(struct elf *elf, struct section *base) { char *relaname; struct section *sec; relaname = malloc(strlen(base->name) + strlen(".rela") + 1); if (!relaname) { perror("malloc"); return NULL; } strcpy(relaname, ".rela"); strcat(relaname, base->name); sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0); free(relaname); if (!sec) return NULL; base->rela = sec; sec->base = base; sec->sh.sh_type = SHT_RELA; sec->sh.sh_addralign = 8; sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; sec->sh.sh_info = base->idx; sec->sh.sh_flags = SHF_INFO_LINK; return sec; } int elf_rebuild_rela_section(struct section *sec) { struct rela *rela; int nr, idx = 0, size; GElf_Rela *relas; nr = 0; list_for_each_entry(rela, &sec->rela_list, list) nr++; size = nr * sizeof(*relas); relas = malloc(size); if (!relas) { perror("malloc"); return -1; } sec->data->d_buf = relas; sec->data->d_size = size; sec->sh.sh_size = size; idx = 0; list_for_each_entry(rela, &sec->rela_list, list) { relas[idx].r_offset = rela->offset; relas[idx].r_addend = rela->addend; relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type); idx++; } return 0; } int elf_write(const struct elf *elf) { struct section *sec; Elf_Scn *s; /* Update section headers for changed sections: */ list_for_each_entry(sec, &elf->sections, list) { if (sec->changed) { s = elf_getscn(elf->elf, sec->idx); if (!s) { WARN_ELF("elf_getscn"); return -1; } if (!gelf_update_shdr(s, &sec->sh)) { WARN_ELF("gelf_update_shdr"); return -1; } } } /* Make sure the new section header entries get updated properly. */ elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); /* Write all changes to the file. */ if (elf_update(elf->elf, ELF_C_WRITE) < 0) { WARN_ELF("elf_update"); return -1; } return 0; } void elf_close(struct elf *elf) { struct section *sec, *tmpsec; struct symbol *sym, *tmpsym; struct rela *rela, *tmprela; if (elf->elf) elf_end(elf->elf); if (elf->fd > 0) close(elf->fd); list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { list_del(&sym->list); hash_del(&sym->hash); free(sym); } list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { list_del(&rela->list); hash_del(&rela->hash); free(rela); } list_del(&sec->list); free(sec); } free(elf); }