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linux/tools/objtool/elf.c

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// 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 <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <libgen.h>
#include <ctype.h>
#include <linux/interval_tree_generic.h>
#include <objtool/builtin.h>
#include <objtool/elf.h>
#include <objtool/warn.h>
#define ALIGN_UP(x, align_to) (((x) + ((align_to)-1)) & ~((align_to)-1))
#define ALIGN_UP_POW2(x) (1U << ((8 * sizeof(x)) - __builtin_clz((x) - 1U)))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
static inline u32 str_hash(const char *str)
{
return jhash(str, strlen(str), 0);
}
#define __elf_table(name) (elf->name##_hash)
#define __elf_bits(name) (elf->name##_bits)
#define __elf_table_entry(name, key) \
__elf_table(name)[hash_min(key, __elf_bits(name))]
#define elf_hash_add(name, node, key) \
({ \
struct elf_hash_node *__node = node; \
__node->next = __elf_table_entry(name, key); \
__elf_table_entry(name, key) = __node; \
})
static inline void __elf_hash_del(struct elf_hash_node *node,
struct elf_hash_node **head)
{
struct elf_hash_node *cur, *prev;
if (node == *head) {
*head = node->next;
return;
}
for (prev = NULL, cur = *head; cur; prev = cur, cur = cur->next) {
if (cur == node) {
prev->next = cur->next;
break;
}
}
}
#define elf_hash_del(name, node, key) \
__elf_hash_del(node, &__elf_table_entry(name, key))
#define elf_list_entry(ptr, type, member) \
({ \
typeof(ptr) __ptr = (ptr); \
__ptr ? container_of(__ptr, type, member) : NULL; \
})
#define elf_hash_for_each_possible(name, obj, member, key) \
for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \
obj; \
obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))
#define elf_alloc_hash(name, size) \
({ \
__elf_bits(name) = max(10, ilog2(size)); \
__elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \
PROT_READ|PROT_WRITE, \
MAP_PRIVATE|MAP_ANON, -1, 0); \
if (__elf_table(name) == (void *)-1L) { \
ERROR_GLIBC("mmap fail " #name); \
__elf_table(name) = NULL; \
} \
__elf_table(name); \
})
static inline unsigned long __sym_start(struct symbol *s)
{
return s->offset;
}
static inline unsigned long __sym_last(struct symbol *s)
{
return s->offset + (s->len ? s->len - 1 : 0);
}
INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
__sym_start, __sym_last, static inline __maybe_unused,
__sym)
#define __sym_for_each(_iter, _tree, _start, _end) \
for (_iter = __sym_iter_first((_tree), (_start), (_end)); \
_iter; _iter = __sym_iter_next(_iter, (_start), (_end)))
struct symbol_hole {
unsigned long key;
const struct symbol *sym;
};
/*
* Find the last symbol before @offset.
*/
static int symbol_hole_by_offset(const void *key, const struct rb_node *node)
{
const struct symbol *s = rb_entry(node, struct symbol, node);
struct symbol_hole *sh = (void *)key;
if (sh->key < s->offset)
return -1;
if (sh->key >= s->offset + s->len) {
sh->sym = s;
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(section_name, 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(section, 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(symbol, 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_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
struct symbol *sym;
__sym_for_each(sym, tree, offset, offset) {
if (sym->offset == offset && !is_sec_sym(sym))
return sym->alias;
}
return NULL;
}
struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
{
struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
struct symbol *func;
__sym_for_each(func, tree, offset, offset) {
if (func->offset == offset && is_func_sym(func))
return func->alias;
}
return NULL;
}
struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
{
struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
struct symbol *sym = NULL, *tmp;
__sym_for_each(tmp, tree, offset, offset) {
if (tmp->len) {
if (!sym) {
sym = tmp;
continue;
}
if (sym->offset != tmp->offset || sym->len != tmp->len) {
/*
* In the rare case of overlapping symbols,
* pick the smaller one.
*
* TODO: outlaw overlapping symbols
*/
if (tmp->len < sym->len)
sym = tmp;
}
}
}
return sym ? sym->alias : NULL;
}
/*
* Returns size of hole starting at @offset.
*/
int find_symbol_hole_containing(const struct section *sec, unsigned long offset)
{
struct symbol_hole hole = {
.key = offset,
.sym = NULL,
};
struct rb_node *n;
struct symbol *s;
/*
* Find the rightmost symbol for which @offset is after it.
*/
n = rb_find(&hole, &sec->symbol_tree.rb_root, symbol_hole_by_offset);
/* found a symbol that contains @offset */
if (n)
return 0; /* not a hole */
/*
* @offset >= sym->offset + sym->len, find symbol after it.
* When hole.sym is empty, use the first node to compute the hole.
* If there is no symbol in the section, the first node will be NULL,
* in which case, -1 is returned to skip the whole section.
*/
if (hole.sym)
n = rb_next(&hole.sym->node);
else
n = rb_first_cached(&sec->symbol_tree);
if (!n)
return -1; /* until end of address space */
/* hole until start of next symbol */
s = rb_entry(n, struct symbol, node);
return s->offset - offset;
}
struct symbol *find_func_containing(struct section *sec, unsigned long offset)
{
struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
struct symbol *func;
__sym_for_each(func, tree, offset, offset) {
if (is_func_sym(func))
return func->alias;
}
return NULL;
}
struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
{
struct symbol *sym;
elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
if (!strcmp(sym->name, name))
return sym;
}
return NULL;
}
/* Find local symbol with matching STT_FILE */
static struct symbol *find_local_symbol_by_file_and_name(const struct elf *elf,
struct symbol *file,
const char *name)
{
struct symbol *sym;
elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
if (sym->bind == STB_LOCAL && sym->file == file &&
!strcmp(sym->name, name)) {
return sym;
}
}
return NULL;
}
struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *name)
{
struct symbol *sym;
elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
if (!strcmp(sym->name, name) && !is_local_sym(sym))
return sym;
}
return NULL;
}
struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len)
{
struct reloc *reloc, *r = NULL;
struct section *rsec;
unsigned long o;
rsec = sec->rsec;
if (!rsec)
return NULL;
for_offset_range(o, offset, offset + len) {
elf_hash_for_each_possible(reloc, reloc, hash,
sec_offset_hash(rsec, o)) {
if (reloc->sec != rsec)
continue;
if (reloc_offset(reloc) >= offset &&
reloc_offset(reloc) < offset + len) {
if (!r || reloc_offset(reloc) < reloc_offset(r))
r = reloc;
}
}
if (r)
return r;
}
return NULL;
}
struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
{
return find_reloc_by_dest_range(elf, sec, offset, 1);
}
static bool is_dwarf_section(struct section *sec)
{
return !strncmp(sec->name, ".debug_", 7);
}
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, &sections_nr)) {
ERROR_ELF("elf_getshdrnum");
return -1;
}
if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
ERROR_ELF("elf_getshdrstrndx");
return -1;
}
if (!elf_alloc_hash(section, sections_nr) ||
!elf_alloc_hash(section_name, sections_nr))
return -1;
elf->section_data = calloc(sections_nr, sizeof(*sec));
if (!elf->section_data) {
ERROR_GLIBC("calloc");
return -1;
}
for (i = 0; i < sections_nr; i++) {
sec = &elf->section_data[i];
INIT_LIST_HEAD(&sec->symbol_list);
s = elf_getscn(elf->elf, i);
if (!s) {
ERROR_ELF("elf_getscn");
return -1;
}
sec->idx = elf_ndxscn(s);
if (!gelf_getshdr(s, &sec->sh)) {
ERROR_ELF("gelf_getshdr");
return -1;
}
sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
if (!sec->name) {
ERROR_ELF("elf_strptr");
return -1;
}
if (sec_size(sec) != 0 && !is_dwarf_section(sec)) {
sec->data = elf_getdata(s, NULL);
if (!sec->data) {
ERROR_ELF("elf_getdata");
return -1;
}
if (sec->data->d_off != 0 ||
sec->data->d_size != sec_size(sec)) {
ERROR("unexpected data attributes for %s", sec->name);
return -1;
}
}
list_add_tail(&sec->list, &elf->sections);
elf_hash_add(section, &sec->hash, sec->idx);
elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
if (is_reloc_sec(sec))
elf->num_relocs += sec_num_entries(sec);
}
if (opts.stats) {
printf("nr_sections: %lu\n", (unsigned long)sections_nr);
printf("section_bits: %d\n", elf->section_bits);
}
/* sanity check, one more call to elf_nextscn() should return NULL */
if (elf_nextscn(elf->elf, s)) {
ERROR("section entry mismatch");
return -1;
}
return 0;
}
static const char *demangle_name(struct symbol *sym)
{
char *str;
if (!is_local_sym(sym))
return sym->name;
if (!is_func_sym(sym) && !is_object_sym(sym))
return sym->name;
if (!strstarts(sym->name, "__UNIQUE_ID_") && !strchr(sym->name, '.'))
return sym->name;
str = strdup(sym->name);
if (!str) {
ERROR_GLIBC("strdup");
return NULL;
}
for (int i = strlen(str) - 1; i >= 0; i--) {
char c = str[i];
if (!isdigit(c) && c != '.') {
str[i + 1] = '\0';
break;
}
}
return str;
}
static int elf_add_symbol(struct elf *elf, struct symbol *sym)
{
struct list_head *entry;
struct rb_node *pnode;
struct symbol *iter;
INIT_LIST_HEAD(&sym->pv_target);
sym->alias = sym;
sym->type = GELF_ST_TYPE(sym->sym.st_info);
sym->bind = GELF_ST_BIND(sym->sym.st_info);
if (is_file_sym(sym))
elf->num_files++;
sym->offset = sym->sym.st_value;
sym->len = sym->sym.st_size;
__sym_for_each(iter, &sym->sec->symbol_tree, sym->offset, sym->offset) {
if (!is_undef_sym(iter) && iter->offset == sym->offset &&
iter->type == sym->type && iter->len == sym->len)
iter->alias = sym;
}
__sym_insert(sym, &sym->sec->symbol_tree);
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);
list_add_tail(&sym->global_list, &elf->symbols);
elf_hash_add(symbol, &sym->hash, sym->idx);
elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
if (is_func_sym(sym) &&
(strstarts(sym->name, "__pfx_") ||
strstarts(sym->name, "__cfi_") ||
strstarts(sym->name, "__pi___pfx_") ||
strstarts(sym->name, "__pi___cfi_")))
sym->prefix = 1;
if (strstarts(sym->name, ".klp.sym"))
sym->klp = 1;
if (!sym->klp && !is_sec_sym(sym) && strstr(sym->name, ".cold")) {
sym->cold = 1;
/*
* Clang doesn't mark cold subfunctions as STT_FUNC, which
* breaks several objtool assumptions. Fake it.
*/
sym->type = STT_FUNC;
}
sym->pfunc = sym->cfunc = sym;
sym->demangled_name = demangle_name(sym);
if (!sym->demangled_name)
return -1;
return 0;
}
static int read_symbols(struct elf *elf)
{
struct section *symtab, *symtab_shndx, *sec;
struct symbol *sym, *pfunc, *file = NULL;
int symbols_nr, i;
char *coldstr;
Elf_Data *shndx_data = NULL;
Elf32_Word shndx;
symtab = find_section_by_name(elf, ".symtab");
if (symtab) {
symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
if (symtab_shndx)
shndx_data = symtab_shndx->data;
symbols_nr = sec_num_entries(symtab);
} else {
/*
* A missing symbol table is actually possible if it's an empty
* .o file. This can happen for thunk_64.o. Make sure to at
* least allocate the symbol hash tables so we can do symbol
* lookups without crashing.
*/
symbols_nr = 0;
}
if (!elf_alloc_hash(symbol, symbols_nr) ||
!elf_alloc_hash(symbol_name, symbols_nr))
return -1;
elf->symbol_data = calloc(symbols_nr, sizeof(*sym));
if (!elf->symbol_data) {
ERROR_GLIBC("calloc");
return -1;
}
INIT_LIST_HEAD(&elf->symbols);
for (i = 0; i < symbols_nr; i++) {
sym = &elf->symbol_data[i];
sym->idx = i;
if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
&shndx)) {
ERROR_ELF("gelf_getsymshndx");
return -1;
}
sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
sym->sym.st_name);
if (!sym->name) {
ERROR_ELF("elf_strptr");
return -1;
}
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) {
ERROR("couldn't find section for symbol %s", sym->name);
return -1;
}
if (GELF_ST_TYPE(sym->sym.st_info) == STT_SECTION) {
sym->name = sym->sec->name;
sym->sec->sym = sym;
}
} else
sym->sec = find_section_by_index(elf, 0);
if (elf_add_symbol(elf, sym))
return -1;
if (sym->type == STT_FILE)
file = sym;
else if (sym->bind == STB_LOCAL)
sym->file = file;
}
if (opts.stats) {
printf("nr_symbols: %lu\n", (unsigned long)symbols_nr);
printf("symbol_bits: %d\n", elf->symbol_bits);
}
/* Create parent/child links for any cold subfunctions */
list_for_each_entry(sec, &elf->sections, list) {
sec_for_each_sym(sec, sym) {
char *pname;
size_t pnamelen;
if (!sym->cold)
continue;
coldstr = strstr(sym->name, ".cold");
if (!coldstr) {
ERROR("%s(): cold subfunction without \".cold\"?", sym->name);
return -1;
}
pnamelen = coldstr - sym->name;
pname = strndup(sym->name, pnamelen);
if (!pname) {
ERROR("%s(): failed to allocate memory", sym->name);
return -1;
}
pfunc = find_local_symbol_by_file_and_name(elf, sym->file, pname);
if (!pfunc)
pfunc = find_global_symbol_by_name(elf, pname);
free(pname);
if (!pfunc) {
ERROR("%s(): can't find parent function", sym->name);
return -1;
}
sym->pfunc = pfunc->alias;
pfunc->cfunc = sym;
pfunc->alias->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;
}
static int mark_group_syms(struct elf *elf)
{
struct section *symtab, *sec;
struct symbol *sym;
symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
ERROR("no .symtab");
return -1;
}
for_each_sec(elf, sec) {
if (sec->sh.sh_type == SHT_GROUP &&
sec->sh.sh_link == symtab->idx) {
sym = find_symbol_by_index(elf, sec->sh.sh_info);
if (!sym) {
ERROR("%s: can't find SHT_GROUP signature symbol",
sec->name);
return -1;
}
sym->group_sec = sec;
}
}
return 0;
}
/*
* @sym's idx has changed. Update the relocs which reference it.
*/
static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym)
{
struct reloc *reloc;
for (reloc = sym->relocs; reloc; reloc = sym_next_reloc(reloc))
set_reloc_sym(elf, reloc, reloc->sym->idx);
return 0;
}
/*
* The libelf API is terrible; gelf_update_sym*() takes a data block relative
* index value, *NOT* the symbol index. As such, iterate the data blocks and
* adjust index until it fits.
*
* If no data block is found, allow adding a new data block provided the index
* is only one past the end.
*/
static int elf_update_symbol(struct elf *elf, struct section *symtab,
struct section *symtab_shndx, struct symbol *sym)
{
Elf32_Word shndx;
Elf_Data *symtab_data = NULL, *shndx_data = NULL;
Elf64_Xword entsize = symtab->sh.sh_entsize;
int max_idx, idx = sym->idx;
Elf_Scn *s, *t = NULL;
bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
sym->sym.st_shndx != SHN_XINDEX;
shndx = is_special_shndx ? sym->sym.st_shndx : sym->sec->idx;
s = elf_getscn(elf->elf, symtab->idx);
if (!s) {
ERROR_ELF("elf_getscn");
return -1;
}
if (symtab_shndx) {
t = elf_getscn(elf->elf, symtab_shndx->idx);
if (!t) {
ERROR_ELF("elf_getscn");
return -1;
}
}
for (;;) {
/* get next data descriptor for the relevant sections */
symtab_data = elf_getdata(s, symtab_data);
if (t)
shndx_data = elf_getdata(t, shndx_data);
/* end-of-list */
if (!symtab_data) {
/*
* Over-allocate to avoid O(n^2) symbol creation
* behaviour. The down side is that libelf doesn't
* like this; see elf_truncate_section() for the fixup.
*/
int num = max(1U, sym->idx/3);
void *buf;
if (idx) {
/* we don't do holes in symbol tables */
ERROR("index out of range");
return -1;
}
/* if @idx == 0, it's the next contiguous entry, create it */
symtab_data = elf_newdata(s);
if (t)
shndx_data = elf_newdata(t);
buf = calloc(num, entsize);
if (!buf) {
ERROR_GLIBC("calloc");
return -1;
}
symtab_data->d_buf = buf;
symtab_data->d_size = num * entsize;
symtab_data->d_align = 1;
symtab_data->d_type = ELF_T_SYM;
mark_sec_changed(elf, symtab, true);
symtab->truncate = true;
if (t) {
buf = calloc(num, sizeof(Elf32_Word));
if (!buf) {
ERROR_GLIBC("calloc");
return -1;
}
shndx_data->d_buf = buf;
shndx_data->d_size = num * sizeof(Elf32_Word);
shndx_data->d_align = sizeof(Elf32_Word);
shndx_data->d_type = ELF_T_WORD;
mark_sec_changed(elf, symtab_shndx, true);
symtab_shndx->truncate = true;
}
break;
}
/* empty blocks should not happen */
if (!symtab_data->d_size) {
ERROR("zero size data");
return -1;
}
/* is this the right block? */
max_idx = symtab_data->d_size / entsize;
if (idx < max_idx)
break;
/* adjust index and try again */
idx -= max_idx;
}
/* something went side-ways */
if (idx < 0) {
ERROR("negative index");
return -1;
}
/* setup extended section index magic and write the symbol */
if (shndx < SHN_LORESERVE || is_special_shndx) {
sym->sym.st_shndx = shndx;
if (!shndx_data)
shndx = 0;
} else {
sym->sym.st_shndx = SHN_XINDEX;
if (!shndx_data) {
ERROR("no .symtab_shndx");
return -1;
}
}
if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
ERROR_ELF("gelf_update_symshndx");
return -1;
}
return 0;
}
struct symbol *elf_create_symbol(struct elf *elf, const char *name,
struct section *sec, unsigned int bind,
unsigned int type, unsigned long offset,
size_t size)
{
struct section *symtab, *symtab_shndx;
Elf32_Word first_non_local, new_idx;
struct symbol *old, *sym;
sym = calloc(1, sizeof(*sym));
if (!sym) {
ERROR_GLIBC("calloc");
return NULL;
}
sym->name = strdup(name);
if (!sym->name) {
ERROR_GLIBC("strdup");
return NULL;
}
if (type != STT_SECTION) {
sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
if (sym->sym.st_name == -1)
return NULL;
}
if (sec) {
sym->sec = sec;
} else {
sym->sec = find_section_by_index(elf, 0);
if (!sym->sec) {
ERROR("no NULL section");
return NULL;
}
}
sym->sym.st_info = GELF_ST_INFO(bind, type);
sym->sym.st_value = offset;
sym->sym.st_size = size;
symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
ERROR("no .symtab");
return NULL;
}
symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
new_idx = sec_num_entries(symtab);
if (bind != STB_LOCAL)
goto non_local;
/*
* Move the first global symbol, as per sh_info, into a new, higher
* symbol index. This frees up a spot for a new local symbol.
*/
first_non_local = symtab->sh.sh_info;
old = find_symbol_by_index(elf, first_non_local);
if (old) {
elf_hash_del(symbol, &old->hash, old->idx);
elf_hash_add(symbol, &old->hash, new_idx);
old->idx = new_idx;
if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
ERROR("elf_update_symbol move");
return NULL;
}
if (elf_update_sym_relocs(elf, old))
return NULL;
if (old->group_sec) {
old->group_sec->sh.sh_info = new_idx;
mark_sec_changed(elf, old->group_sec, true);
}
new_idx = first_non_local;
}
/*
* Either way, we will add a LOCAL symbol.
*/
symtab->sh.sh_info += 1;
non_local:
sym->idx = new_idx;
if (sym->idx && elf_update_symbol(elf, symtab, symtab_shndx, sym))
return NULL;
symtab->sh.sh_size += symtab->sh.sh_entsize;
mark_sec_changed(elf, symtab, true);
if (symtab_shndx) {
symtab_shndx->sh.sh_size += sizeof(Elf32_Word);
mark_sec_changed(elf, symtab_shndx, true);
}
if (elf_add_symbol(elf, sym))
return NULL;
return sym;
}
struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec)
{
struct symbol *sym = calloc(1, sizeof(*sym));
sym = elf_create_symbol(elf, sec->name, sec, STB_LOCAL, STT_SECTION, 0, 0);
if (!sym)
return NULL;
sec->sym = sym;
return sym;
}
struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
unsigned int reloc_idx, unsigned long offset,
struct symbol *sym, s64 addend, unsigned int type)
{
struct reloc *reloc, empty = { 0 };
if (reloc_idx >= sec_num_entries(rsec)) {
ERROR("%s: bad reloc_idx %u for %s with %d relocs",
__func__, reloc_idx, rsec->name, sec_num_entries(rsec));
return NULL;
}
reloc = &rsec->relocs[reloc_idx];
if (memcmp(reloc, &empty, sizeof(empty))) {
ERROR("%s: %s: reloc %d already initialized!",
__func__, rsec->name, reloc_idx);
return NULL;
}
reloc->sec = rsec;
reloc->sym = sym;
set_reloc_offset(elf, reloc, offset);
set_reloc_sym(elf, reloc, sym->idx);
set_reloc_type(elf, reloc, type);
set_reloc_addend(elf, reloc, addend);
elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
set_sym_next_reloc(reloc, sym->relocs);
sym->relocs = reloc;
return reloc;
}
struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec,
unsigned long offset,
unsigned int reloc_idx,
struct section *insn_sec,
unsigned long insn_off)
{
struct symbol *sym = insn_sec->sym;
s64 addend = insn_off;
if (!is_text_sec(insn_sec)) {
ERROR("bad call to %s() for data symbol %s", __func__, sym->name);
return NULL;
}
if (!sym) {
/*
* Due to how weak functions work, we must use section based
* relocations. Symbol based relocations would result in the
* weak and non-weak function annotations being overlaid on the
* non-weak function after linking.
*/
sym = elf_create_section_symbol(elf, insn_sec);
if (!sym)
return NULL;
}
return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
elf_text_rela_type(elf));
}
struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
unsigned long offset,
unsigned int reloc_idx,
struct symbol *sym,
s64 addend)
{
if (is_text_sec(sec)) {
ERROR("bad call to %s() for text symbol %s", __func__, sym->name);
return NULL;
}
return elf_init_reloc(elf, sec->rsec, reloc_idx, offset, sym, addend,
elf_data_rela_type(elf));
}
static int read_relocs(struct elf *elf)
{
unsigned long nr_reloc, max_reloc = 0;
struct section *rsec;
struct reloc *reloc;
unsigned int symndx;
struct symbol *sym;
int i;
if (!elf_alloc_hash(reloc, elf->num_relocs))
return -1;
list_for_each_entry(rsec, &elf->sections, list) {
if (!is_reloc_sec(rsec))
continue;
rsec->base = find_section_by_index(elf, rsec->sh.sh_info);
if (!rsec->base) {
ERROR("can't find base section for reloc section %s", rsec->name);
return -1;
}
rsec->base->rsec = rsec;
/* nr_alloc_relocs=0: libelf owns d_buf */
rsec->nr_alloc_relocs = 0;
rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));
if (!rsec->relocs) {
ERROR_GLIBC("calloc");
return -1;
}
nr_reloc = 0;
for (i = 0; i < sec_num_entries(rsec); i++) {
reloc = &rsec->relocs[i];
reloc->sec = rsec;
symndx = reloc_sym(reloc);
reloc->sym = sym = find_symbol_by_index(elf, symndx);
if (!reloc->sym) {
ERROR("can't find reloc entry symbol %d for %s", symndx, rsec->name);
return -1;
}
elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
set_sym_next_reloc(reloc, sym->relocs);
sym->relocs = reloc;
nr_reloc++;
}
max_reloc = max(max_reloc, nr_reloc);
}
if (opts.stats) {
printf("max_reloc: %lu\n", max_reloc);
printf("num_relocs: %lu\n", elf->num_relocs);
printf("reloc_bits: %d\n", elf->reloc_bits);
}
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) {
ERROR_GLIBC("malloc");
return NULL;
}
memset(elf, 0, sizeof(*elf));
INIT_LIST_HEAD(&elf->sections);
elf->fd = open(name, flags);
if (elf->fd == -1) {
fprintf(stderr, "objtool: Can't open '%s': %s\n",
name, strerror(errno));
goto err;
}
elf->name = strdup(name);
if (!elf->name) {
ERROR_GLIBC("strdup");
return NULL;
}
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) {
ERROR_ELF("elf_begin");
goto err;
}
if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
ERROR_ELF("gelf_getehdr");
goto err;
}
if (read_sections(elf))
goto err;
if (read_symbols(elf))
goto err;
if (mark_group_syms(elf))
goto err;
if (read_relocs(elf))
goto err;
return elf;
err:
elf_close(elf);
return NULL;
}
struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
{
struct section *null, *symtab, *strtab, *shstrtab;
char *dir, *base, *tmp_name;
struct symbol *sym;
struct elf *elf;
elf_version(EV_CURRENT);
elf = calloc(1, sizeof(*elf));
if (!elf) {
ERROR_GLIBC("calloc");
return NULL;
}
INIT_LIST_HEAD(&elf->sections);
dir = strdup(name);
if (!dir) {
ERROR_GLIBC("strdup");
return NULL;
}
dir = dirname(dir);
base = strdup(name);
if (!base) {
ERROR_GLIBC("strdup");
return NULL;
}
base = basename(base);
tmp_name = malloc(256);
if (!tmp_name) {
ERROR_GLIBC("malloc");
return NULL;
}
snprintf(tmp_name, 256, "%s/%s.XXXXXX", dir, base);
elf->fd = mkstemp(tmp_name);
if (elf->fd == -1) {
ERROR_GLIBC("can't create tmp file");
exit(1);
}
elf->tmp_name = tmp_name;
elf->name = strdup(name);
if (!elf->name) {
ERROR_GLIBC("strdup");
return NULL;
}
elf->elf = elf_begin(elf->fd, ELF_C_WRITE, NULL);
if (!elf->elf) {
ERROR_ELF("elf_begin");
return NULL;
}
if (!gelf_newehdr(elf->elf, ELFCLASS64)) {
ERROR_ELF("gelf_newehdr");
return NULL;
}
memcpy(&elf->ehdr, ehdr, sizeof(elf->ehdr));
if (!gelf_update_ehdr(elf->elf, &elf->ehdr)) {
ERROR_ELF("gelf_update_ehdr");
return NULL;
}
INIT_LIST_HEAD(&elf->symbols);
if (!elf_alloc_hash(section, 1000) ||
!elf_alloc_hash(section_name, 1000) ||
!elf_alloc_hash(symbol, 10000) ||
!elf_alloc_hash(symbol_name, 10000) ||
!elf_alloc_hash(reloc, 100000))
return NULL;
null = elf_create_section(elf, NULL, 0, 0, SHT_NULL, 0, 0);
shstrtab = elf_create_section(elf, NULL, 0, 0, SHT_STRTAB, 1, 0);
strtab = elf_create_section(elf, NULL, 0, 0, SHT_STRTAB, 1, 0);
if (!null || !shstrtab || !strtab)
return NULL;
null->name = "";
shstrtab->name = ".shstrtab";
strtab->name = ".strtab";
null->sh.sh_name = elf_add_string(elf, shstrtab, null->name);
shstrtab->sh.sh_name = elf_add_string(elf, shstrtab, shstrtab->name);
strtab->sh.sh_name = elf_add_string(elf, shstrtab, strtab->name);
if (null->sh.sh_name == -1 || shstrtab->sh.sh_name == -1 || strtab->sh.sh_name == -1)
return NULL;
elf_hash_add(section_name, &null->name_hash, str_hash(null->name));
elf_hash_add(section_name, &strtab->name_hash, str_hash(strtab->name));
elf_hash_add(section_name, &shstrtab->name_hash, str_hash(shstrtab->name));
if (elf_add_string(elf, strtab, "") == -1)
return NULL;
symtab = elf_create_section(elf, ".symtab", 0x18, 0x18, SHT_SYMTAB, 0x8, 0);
if (!symtab)
return NULL;
symtab->sh.sh_link = strtab->idx;
symtab->sh.sh_info = 1;
elf->ehdr.e_shstrndx = shstrtab->idx;
if (!gelf_update_ehdr(elf->elf, &elf->ehdr)) {
ERROR_ELF("gelf_update_ehdr");
return NULL;
}
sym = calloc(1, sizeof(*sym));
if (!sym) {
ERROR_GLIBC("calloc");
return NULL;
}
sym->name = "";
sym->sec = null;
elf_add_symbol(elf, sym);
return elf;
}
unsigned int elf_add_string(struct elf *elf, struct section *strtab, const char *str)
{
unsigned int offset;
if (!strtab)
strtab = find_section_by_name(elf, ".strtab");
if (!strtab) {
ERROR("can't find .strtab section");
return -1;
}
if (!strtab->sh.sh_addralign) {
ERROR("'%s': invalid sh_addralign", strtab->name);
return -1;
}
offset = ALIGN_UP(strtab->sh.sh_size, strtab->sh.sh_addralign);
if (!elf_add_data(elf, strtab, str, strlen(str) + 1))
return -1;
return offset;
}
void *elf_add_data(struct elf *elf, struct section *sec, const void *data, size_t size)
{
unsigned long offset;
Elf_Scn *s;
if (!sec->sh.sh_addralign) {
ERROR("'%s': invalid sh_addralign", sec->name);
return NULL;
}
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
ERROR_ELF("elf_getscn");
return NULL;
}
sec->data = elf_newdata(s);
if (!sec->data) {
ERROR_ELF("elf_newdata");
return NULL;
}
sec->data->d_buf = calloc(1, size);
if (!sec->data->d_buf) {
ERROR_GLIBC("calloc");
return NULL;
}
if (data)
memcpy(sec->data->d_buf, data, size);
sec->data->d_size = size;
sec->data->d_align = 1;
offset = ALIGN_UP(sec->sh.sh_size, sec->sh.sh_addralign);
sec->sh.sh_size = offset + size;
mark_sec_changed(elf, sec, true);
return sec->data->d_buf;
}
struct section *elf_create_section(struct elf *elf, const char *name,
size_t size, size_t entsize,
unsigned int type, unsigned int align,
unsigned int flags)
{
struct section *sec, *shstrtab;
Elf_Scn *s;
if (name && find_section_by_name(elf, name)) {
ERROR("section '%s' already exists", name);
return NULL;
}
sec = calloc(1, sizeof(*sec));
if (!sec) {
ERROR_GLIBC("calloc");
return NULL;
}
INIT_LIST_HEAD(&sec->symbol_list);
/* don't actually create the section, just the data structures */
if (type == SHT_NULL)
goto add;
s = elf_newscn(elf->elf);
if (!s) {
ERROR_ELF("elf_newscn");
return NULL;
}
sec->idx = elf_ndxscn(s);
if (size) {
sec->data = elf_newdata(s);
if (!sec->data) {
ERROR_ELF("elf_newdata");
return NULL;
}
sec->data->d_size = size;
sec->data->d_align = 1;
sec->data->d_buf = calloc(1, size);
if (!sec->data->d_buf) {
ERROR_GLIBC("calloc");
return NULL;
}
}
if (!gelf_getshdr(s, &sec->sh)) {
ERROR_ELF("gelf_getshdr");
return NULL;
}
sec->sh.sh_size = size;
sec->sh.sh_entsize = entsize;
sec->sh.sh_type = type;
sec->sh.sh_addralign = align;
sec->sh.sh_flags = flags;
if (name) {
sec->name = strdup(name);
if (!sec->name) {
ERROR("strdup");
return NULL;
}
/* 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) {
ERROR("can't find .shstrtab or .strtab");
return NULL;
}
}
sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
if (sec->sh.sh_name == -1)
return NULL;
elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name));
}
add:
list_add_tail(&sec->list, &elf->sections);
elf_hash_add(section, &sec->hash, sec->idx);
mark_sec_changed(elf, sec, true);
return sec;
}
static int elf_alloc_reloc(struct elf *elf, struct section *rsec)
{
struct reloc *old_relocs, *old_relocs_end, *new_relocs;
unsigned int nr_relocs_old = sec_num_entries(rsec);
unsigned int nr_relocs_new = nr_relocs_old + 1;
unsigned long nr_alloc;
struct symbol *sym;
if (!rsec->data) {
rsec->data = elf_newdata(elf_getscn(elf->elf, rsec->idx));
if (!rsec->data) {
ERROR_ELF("elf_newdata");
return -1;
}
rsec->data->d_align = 1;
rsec->data->d_type = ELF_T_RELA;
rsec->data->d_buf = NULL;
}
rsec->data->d_size = nr_relocs_new * elf_rela_size(elf);
rsec->sh.sh_size = rsec->data->d_size;
nr_alloc = MAX(64, ALIGN_UP_POW2(nr_relocs_new));
if (nr_alloc <= rsec->nr_alloc_relocs)
return 0;
if (rsec->data->d_buf && !rsec->nr_alloc_relocs) {
void *orig_buf = rsec->data->d_buf;
/*
* The original d_buf is owned by libelf so it can't be
* realloced.
*/
rsec->data->d_buf = malloc(nr_alloc * elf_rela_size(elf));
if (!rsec->data->d_buf) {
ERROR_GLIBC("malloc");
return -1;
}
memcpy(rsec->data->d_buf, orig_buf,
nr_relocs_old * elf_rela_size(elf));
} else {
rsec->data->d_buf = realloc(rsec->data->d_buf,
nr_alloc * elf_rela_size(elf));
if (!rsec->data->d_buf) {
ERROR_GLIBC("realloc");
return -1;
}
}
rsec->nr_alloc_relocs = nr_alloc;
old_relocs = rsec->relocs;
new_relocs = calloc(nr_alloc, sizeof(struct reloc));
if (!new_relocs) {
ERROR_GLIBC("calloc");
return -1;
}
if (!old_relocs)
goto done;
/*
* The struct reloc's address has changed. Update all the symbols and
* relocs which reference it.
*/
old_relocs_end = &old_relocs[nr_relocs_old];
for_each_sym(elf, sym) {
struct reloc *reloc;
reloc = sym->relocs;
if (!reloc)
continue;
if (reloc >= old_relocs && reloc < old_relocs_end)
sym->relocs = &new_relocs[reloc - old_relocs];
while (1) {
struct reloc *next_reloc = sym_next_reloc(reloc);
if (!next_reloc)
break;
if (next_reloc >= old_relocs && next_reloc < old_relocs_end)
set_sym_next_reloc(reloc, &new_relocs[next_reloc - old_relocs]);
reloc = next_reloc;
}
}
memcpy(new_relocs, old_relocs, nr_relocs_old * sizeof(struct reloc));
for (int i = 0; i < nr_relocs_old; i++) {
struct reloc *old = &old_relocs[i];
struct reloc *new = &new_relocs[i];
u32 key = reloc_hash(old);
elf_hash_del(reloc, &old->hash, key);
elf_hash_add(reloc, &new->hash, key);
}
free(old_relocs);
done:
rsec->relocs = new_relocs;
return 0;
}
struct section *elf_create_rela_section(struct elf *elf, struct section *sec,
unsigned int nr_relocs)
{
struct section *rsec;
char *rsec_name;
rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
if (!rsec_name) {
ERROR_GLIBC("malloc");
return NULL;
}
strcpy(rsec_name, ".rela");
strcat(rsec_name, sec->name);
rsec = elf_create_section(elf, rsec_name, nr_relocs * elf_rela_size(elf),
elf_rela_size(elf), SHT_RELA, elf_addr_size(elf),
SHF_INFO_LINK);
free(rsec_name);
if (!rsec)
return NULL;
if (nr_relocs) {
rsec->data->d_type = ELF_T_RELA;
rsec->nr_alloc_relocs = nr_relocs;
rsec->relocs = calloc(nr_relocs, sizeof(struct reloc));
if (!rsec->relocs) {
ERROR_GLIBC("calloc");
return NULL;
}
}
rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
rsec->sh.sh_info = sec->idx;
sec->rsec = rsec;
rsec->base = sec;
return rsec;
}
struct reloc *elf_create_reloc(struct elf *elf, struct section *sec,
unsigned long offset,
struct symbol *sym, s64 addend,
unsigned int type)
{
struct section *rsec = sec->rsec;
if (!rsec) {
rsec = elf_create_rela_section(elf, sec, 0);
if (!rsec)
return NULL;
}
if (find_reloc_by_dest(elf, sec, offset)) {
ERROR_FUNC(sec, offset, "duplicate reloc");
return NULL;
}
if (elf_alloc_reloc(elf, rsec))
return NULL;
mark_sec_changed(elf, rsec, true);
return elf_init_reloc(elf, rsec, sec_num_entries(rsec) - 1, offset, sym,
addend, type);
}
struct section *elf_create_section_pair(struct elf *elf, const char *name,
size_t entsize, unsigned int nr,
unsigned int nr_relocs)
{
struct section *sec;
sec = elf_create_section(elf, name, nr * entsize, entsize,
SHT_PROGBITS, 1, SHF_ALLOC);
if (!sec)
return NULL;
if (!elf_create_rela_section(elf, sec, nr_relocs))
return NULL;
return sec;
}
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn)
{
Elf_Data *data = sec->data;
if (data->d_type != ELF_T_BYTE || data->d_off) {
ERROR("write to unexpected data for section: %s", sec->name);
return -1;
}
memcpy(data->d_buf + offset, insn, len);
mark_sec_changed(elf, sec, true);
return 0;
}
/*
* When Elf_Scn::sh_size is smaller than the combined Elf_Data::d_size
* do you:
*
* A) adhere to the section header and truncate the data, or
* B) ignore the section header and write out all the data you've got?
*
* Yes, libelf sucks and we need to manually truncate if we over-allocate data.
*/
static int elf_truncate_section(struct elf *elf, struct section *sec)
{
u64 size = sec_size(sec);
bool truncated = false;
Elf_Data *data = NULL;
Elf_Scn *s;
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
ERROR_ELF("elf_getscn");
return -1;
}
for (;;) {
/* get next data descriptor for the relevant section */
data = elf_getdata(s, data);
if (!data) {
if (size) {
ERROR("end of section data but non-zero size left\n");
return -1;
}
return 0;
}
if (truncated) {
/* when we remove symbols */
ERROR("truncated; but more data\n");
return -1;
}
if (!data->d_size) {
ERROR("zero size data");
return -1;
}
if (data->d_size > size) {
truncated = true;
data->d_size = size;
}
size -= data->d_size;
}
}
int elf_write(struct elf *elf)
{
struct section *sec;
Elf_Scn *s;
/* Update changed relocation sections and section headers: */
list_for_each_entry(sec, &elf->sections, list) {
if (sec->truncate && elf_truncate_section(elf, sec))
return -1;
if (sec_changed(sec)) {
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
ERROR_ELF("elf_getscn");
return -1;
}
/* Note this also flags the section dirty */
if (!gelf_update_shdr(s, &sec->sh)) {
ERROR_ELF("gelf_update_shdr");
return -1;
}
mark_sec_changed(elf, sec, false);
}
}
/* 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) {
ERROR_ELF("elf_update");
return -1;
}
elf->changed = false;
return 0;
}
int elf_close(struct elf *elf)
{
if (elf->elf)
elf_end(elf->elf);
if (elf->fd > 0)
close(elf->fd);
if (elf->tmp_name && rename(elf->tmp_name, elf->name))
return -1;
/*
* NOTE: All remaining allocations are leaked on purpose. Objtool is
* about to exit anyway.
*/
return 0;
}
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