// 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 <[email protected]>
* Copyright (C) 2014 Seth Jennings <[email protected]>
*/
#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 <linux/interval_tree_generic.h>
#include <objtool/builtin.h>
#include <objtool/elf.h>
#include <objtool/warn.h>
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) { \
WARN("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 - 1;
}
INTERVAL_TREE_DEFINE(struct symbol, node, unsigned long, __subtree_last,
__sym_start, __sym_last, static, __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 !section symbol where @offset is after it.
*/
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) {
if (s->type != STT_SECTION)
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 *iter;
__sym_for_each(iter, tree, offset, offset) {
if (iter->offset == offset && iter->type != STT_SECTION)
return iter;
}
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 *iter;
__sym_for_each(iter, tree, offset, offset) {
if (iter->offset == offset && iter->type == STT_FUNC)
return iter;
}
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 *iter;
__sym_for_each(iter, tree, offset, offset) {
if (iter->type != STT_SECTION)
return iter;
}
return 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 */
/* didn't find a symbol for which @offset is after it */
if (!hole.sym)
return 0; /* not a hole */
/* @offset >= sym->offset + sym->len, find symbol after it */
n = rb_next(&hole.sym->node);
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 *iter;
__sym_for_each(iter, tree, offset, offset) {
if (iter->type == STT_FUNC)
return iter;
}
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;
}
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, §ions_nr)) {
WARN_ELF("elf_getshdrnum");
return -1;
}
if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
WARN_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) {
perror("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) {
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 && !is_dwarf_section(sec)) {
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;
}
}
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)) {
WARN("section entry mismatch");
return -1;
}
return 0;
}
static void 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 (sym->type == STT_FILE)
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 (iter->offset == sym->offset && iter->type == sym->type)
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);
elf_hash_add(symbol, &sym->hash, sym->idx);
elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
/*
* Don't store empty STT_NOTYPE symbols in the rbtree. They
* can exist within a function, confusing the sorting.
*/
if (!sym->len)
__sym_remove(sym, &sym->sec->symbol_tree);
}
static int read_symbols(struct elf *elf)
{
struct section *symtab, *symtab_shndx, *sec;
struct symbol *sym, *pfunc;
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) {
perror("calloc");
return -1;
}
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)) {
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;
}
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 (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);
elf_add_symbol(elf, sym);
}
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->type != STT_FUNC)
continue;
if (sym->pfunc == NULL)
sym->pfunc = sym;
if (sym->cfunc == NULL)
sym->cfunc = sym;
coldstr = strstr(sym->name, ".cold");
if (!coldstr)
continue;
pnamelen = coldstr - sym->name;
pname = strndup(sym->name, pnamelen);
if (!pname) {
WARN("%s(): failed to allocate memory",
sym->name);
return -1;
}
pfunc = find_symbol_by_name(elf, pname);
free(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;
}
/*
* @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 = reloc->sym_next_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 = sym->sec ? sym->sec->idx : SHN_UNDEF;
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;
if (is_special_shndx)
shndx = sym->sym.st_shndx;
s = elf_getscn(elf->elf, symtab->idx);
if (!s) {
WARN_ELF("elf_getscn");
return -1;
}
if (symtab_shndx) {
t = elf_getscn(elf->elf, symtab_shndx->idx);
if (!t) {
WARN_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 */
WARN("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) {
WARN("malloc");
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) {
WARN("malloc");
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) {
WARN("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) {
WARN("negative index");
return -1;
}
/* setup extended section index magic and write the symbol */
if ((shndx >= SHN_UNDEF && 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) {
WARN("no .symtab_shndx");
return -1;
}
}
if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
WARN_ELF("gelf_update_symshndx");
return -1;
}
return 0;
}
static struct symbol *
__elf_create_symbol(struct elf *elf, struct symbol *sym)
{
struct section *symtab, *symtab_shndx;
Elf32_Word first_non_local, new_idx;
struct symbol *old;
symtab = find_section_by_name(elf, ".symtab");
if (symtab) {
symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
} else {
WARN("no .symtab");
return NULL;
}
new_idx = sec_num_entries(symtab);
if (GELF_ST_BIND(sym->sym.st_info) != STB_LOCAL)
goto non_local;
/*
* Move the first global symbol, as per sh_info, into a new, higher
* symbol index. This fees 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)) {
WARN("elf_update_symbol move");
return NULL;
}
if (elf_update_sym_relocs(elf, old))
return NULL;
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 (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
WARN("elf_update_symbol");
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);
}
return sym;
}
static struct symbol *
elf_create_section_symbol(struct elf *elf, struct section *sec)
{
struct symbol *sym = calloc(1, sizeof(*sym));
if (!sym) {
perror("malloc");
return NULL;
}
sym->name = sec->name;
sym->sec = sec;
// st_name 0
sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
// st_other 0
// st_value 0
// st_size 0
sym = __elf_create_symbol(elf, sym);
if (sym)
elf_add_symbol(elf, sym);
return sym;
}
static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
struct symbol *
elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
{
struct symbol *sym = calloc(1, sizeof(*sym));
size_t namelen = strlen(orig->name) + sizeof("__pfx_");
char *name = malloc(namelen);
if (!sym || !name) {
perror("malloc");
return NULL;
}
snprintf(name, namelen, "__pfx_%s", orig->name);
sym->name = name;
sym->sec = orig->sec;
sym->sym.st_name = elf_add_string(elf, NULL, name);
sym->sym.st_info = orig->sym.st_info;
sym->sym.st_value = orig->sym.st_value - size;
sym->sym.st_size = size;
sym = __elf_create_symbol(elf, sym);
if (sym)
elf_add_symbol(elf, sym);
return sym;
}
static 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)) {
WARN("%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))) {
WARN("%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));
reloc->sym_next_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;
int addend = insn_off;
if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) {
WARN("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;
insn_sec->sym = sym;
}
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 (sym->sec && (sec->sh.sh_flags & SHF_EXECINSTR)) {
WARN("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) {
WARN("can't find base section for reloc section %s",
rsec->name);
return -1;
}
rsec->base->rsec = rsec;
nr_reloc = 0;
rsec->relocs = calloc(sec_num_entries(rsec), sizeof(*reloc));
if (!rsec->relocs) {
perror("calloc");
return -1;
}
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) {
WARN("can't find reloc entry symbol %d for %s",
symndx, rsec->name);
return -1;
}
elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
reloc->sym_next_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) {
perror("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;
}
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_relocs(elf))
goto err;
return elf;
err:
elf_close(elf);
return NULL;
}
static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
{
Elf_Data *data;
Elf_Scn *s;
int len;
if (!strtab)
strtab = find_section_by_name(elf, ".strtab");
if (!strtab) {
WARN("can't find .strtab section");
return -1;
}
s = elf_getscn(elf->elf, strtab->idx);
if (!s) {
WARN_ELF("elf_getscn");
return -1;
}
data = elf_newdata(s);
if (!data) {
WARN_ELF("elf_newdata");
return -1;
}
data->d_buf = str;
data->d_size = strlen(str) + 1;
data->d_align = 1;
len = strtab->sh.sh_size;
strtab->sh.sh_size += data->d_size;
mark_sec_changed(elf, strtab, true);
return len;
}
struct section *elf_create_section(struct elf *elf, const char *name,
size_t entsize, unsigned int nr)
{
struct section *sec, *shstrtab;
size_t size = entsize * nr;
Elf_Scn *s;
sec = malloc(sizeof(*sec));
if (!sec) {
perror("malloc");
return NULL;
}
memset(sec, 0, sizeof(*sec));
INIT_LIST_HEAD(&sec->symbol_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->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;
}
sec->sh.sh_name = elf_add_string(elf, shstrtab, sec->name);
if (sec->sh.sh_name == -1)
return NULL;
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));
mark_sec_changed(elf, sec, true);
return sec;
}
static struct section *elf_create_rela_section(struct elf *elf,
struct section *sec,
unsigned int reloc_nr)
{
struct section *rsec;
char *rsec_name;
rsec_name = malloc(strlen(sec->name) + strlen(".rela") + 1);
if (!rsec_name) {
perror("malloc");
return NULL;
}
strcpy(rsec_name, ".rela");
strcat(rsec_name, sec->name);
rsec = elf_create_section(elf, rsec_name, elf_rela_size(elf), reloc_nr);
free(rsec_name);
if (!rsec)
return NULL;
rsec->data->d_type = ELF_T_RELA;
rsec->sh.sh_type = SHT_RELA;
rsec->sh.sh_addralign = elf_addr_size(elf);
rsec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
rsec->sh.sh_info = sec->idx;
rsec->sh.sh_flags = SHF_INFO_LINK;
rsec->relocs = calloc(sec_num_entries(rsec), sizeof(struct reloc));
if (!rsec->relocs) {
perror("calloc");
return NULL;
}
sec->rsec = rsec;
rsec->base = sec;
return rsec;
}
struct section *elf_create_section_pair(struct elf *elf, const char *name,
size_t entsize, unsigned int nr,
unsigned int reloc_nr)
{
struct section *sec;
sec = elf_create_section(elf, name, entsize, nr);
if (!sec)
return NULL;
if (!elf_create_rela_section(elf, sec, reloc_nr))
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) {
WARN("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->sh.sh_size;
bool truncated = false;
Elf_Data *data = NULL;
Elf_Scn *s;
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
WARN_ELF("elf_getscn");
return -1;
}
for (;;) {
/* get next data descriptor for the relevant section */
data = elf_getdata(s, data);
if (!data) {
if (size) {
WARN("end of section data but non-zero size left\n");
return -1;
}
return 0;
}
if (truncated) {
/* when we remove symbols */
WARN("truncated; but more data\n");
return -1;
}
if (!data->d_size) {
WARN("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;
if (opts.dryrun)
return 0;
/* Update changed relocation sections and section headers: */
list_for_each_entry(sec, &elf->sections, list) {
if (sec->truncate)
elf_truncate_section(elf, sec);
if (sec_changed(sec)) {
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
WARN_ELF("elf_getscn");
return -1;
}
/* Note this also flags the section dirty */
if (!gelf_update_shdr(s, &sec->sh)) {
WARN_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) {
WARN_ELF("elf_update");
return -1;
}
elf->changed = false;
return 0;
}
void elf_close(struct elf *elf)
{
if (elf->elf)
elf_end(elf->elf);
if (elf->fd > 0)
close(elf->fd);
/*
* NOTE: All remaining allocations are leaked on purpose. Objtool is
* about to exit anyway.
*/
}
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