// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
#include <linux/kernel.h>
#include "libbpf_internal.h"
#include "str_error.h"
/* A SHT_GNU_versym section holds 16-bit words. This bit is set if
* the symbol is hidden and can only be seen when referenced using an
* explicit version number. This is a GNU extension.
*/
#define VERSYM_HIDDEN 0x8000
/* This is the mask for the rest of the data in a word read from a
* SHT_GNU_versym section.
*/
#define VERSYM_VERSION 0x7fff
int elf_open(const char *binary_path, struct elf_fd *elf_fd)
{
char errmsg[STRERR_BUFSIZE];
int fd, ret;
Elf *elf;
elf_fd->elf = NULL;
elf_fd->fd = -1;
if (elf_version(EV_CURRENT) == EV_NONE) {
pr_warn("elf: failed to init libelf for %s\n", binary_path);
return -LIBBPF_ERRNO__LIBELF;
}
fd = open(binary_path, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = -errno;
pr_warn("elf: failed to open %s: %s\n", binary_path,
libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
return ret;
}
elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
if (!elf) {
pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
close(fd);
return -LIBBPF_ERRNO__FORMAT;
}
elf_fd->fd = fd;
elf_fd->elf = elf;
return 0;
}
void elf_close(struct elf_fd *elf_fd)
{
if (!elf_fd)
return;
elf_end(elf_fd->elf);
close(elf_fd->fd);
}
/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
{
while ((scn = elf_nextscn(elf, scn)) != NULL) {
GElf_Shdr sh;
if (!gelf_getshdr(scn, &sh))
continue;
if (sh.sh_type == sh_type)
return scn;
}
return NULL;
}
struct elf_sym {
const char *name;
GElf_Sym sym;
GElf_Shdr sh;
int ver;
bool hidden;
};
struct elf_sym_iter {
Elf *elf;
Elf_Data *syms;
Elf_Data *versyms;
Elf_Data *verdefs;
size_t nr_syms;
size_t strtabidx;
size_t verdef_strtabidx;
size_t next_sym_idx;
struct elf_sym sym;
int st_type;
};
static int elf_sym_iter_new(struct elf_sym_iter *iter,
Elf *elf, const char *binary_path,
int sh_type, int st_type)
{
Elf_Scn *scn = NULL;
GElf_Ehdr ehdr;
GElf_Shdr sh;
memset(iter, 0, sizeof(*iter));
if (!gelf_getehdr(elf, &ehdr)) {
pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
return -EINVAL;
}
scn = elf_find_next_scn_by_type(elf, sh_type, NULL);
if (!scn) {
pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
binary_path);
return -ENOENT;
}
if (!gelf_getshdr(scn, &sh))
return -EINVAL;
iter->strtabidx = sh.sh_link;
iter->syms = elf_getdata(scn, 0);
if (!iter->syms) {
pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
binary_path, elf_errmsg(-1));
return -EINVAL;
}
iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
iter->elf = elf;
iter->st_type = st_type;
/* Version symbol table is meaningful to dynsym only */
if (sh_type != SHT_DYNSYM)
return 0;
scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
if (!scn)
return 0;
iter->versyms = elf_getdata(scn, 0);
scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
if (!scn)
return 0;
iter->verdefs = elf_getdata(scn, 0);
if (!iter->verdefs || !gelf_getshdr(scn, &sh)) {
pr_warn("elf: failed to get verdef ELF section in '%s'\n", binary_path);
return -EINVAL;
}
iter->verdef_strtabidx = sh.sh_link;
return 0;
}
static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
{
struct elf_sym *ret = &iter->sym;
GElf_Sym *sym = &ret->sym;
const char *name = NULL;
GElf_Versym versym;
Elf_Scn *sym_scn;
size_t idx;
for (idx = iter->next_sym_idx; idx < iter->nr_syms; idx++) {
if (!gelf_getsym(iter->syms, idx, sym))
continue;
if (GELF_ST_TYPE(sym->st_info) != iter->st_type)
continue;
name = elf_strptr(iter->elf, iter->strtabidx, sym->st_name);
if (!name)
continue;
sym_scn = elf_getscn(iter->elf, sym->st_shndx);
if (!sym_scn)
continue;
if (!gelf_getshdr(sym_scn, &ret->sh))
continue;
iter->next_sym_idx = idx + 1;
ret->name = name;
ret->ver = 0;
ret->hidden = false;
if (iter->versyms) {
if (!gelf_getversym(iter->versyms, idx, &versym))
continue;
ret->ver = versym & VERSYM_VERSION;
ret->hidden = versym & VERSYM_HIDDEN;
}
return ret;
}
return NULL;
}
static const char *elf_get_vername(struct elf_sym_iter *iter, int ver)
{
GElf_Verdaux verdaux;
GElf_Verdef verdef;
int offset;
if (!iter->verdefs)
return NULL;
offset = 0;
while (gelf_getverdef(iter->verdefs, offset, &verdef)) {
if (verdef.vd_ndx != ver) {
if (!verdef.vd_next)
break;
offset += verdef.vd_next;
continue;
}
if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux))
break;
return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name);
}
return NULL;
}
static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym,
const char *name, size_t name_len, const char *lib_ver)
{
const char *ver_name;
/* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER
* make sure the func part matches the user specified name
*/
if (strncmp(sym->name, name, name_len) != 0)
return false;
/* ...but we don't want a search for "foo" to match 'foo2" also, so any
* additional characters in sname should be of the form "@@LIB".
*/
if (sym->name[name_len] != '\0' && sym->name[name_len] != '@')
return false;
/* If user does not specify symbol version, then we got a match */
if (!lib_ver)
return true;
/* If user specifies symbol version, for dynamic symbols,
* get version name from ELF verdef section for comparison.
*/
if (sh_type == SHT_DYNSYM) {
ver_name = elf_get_vername(iter, sym->ver);
if (!ver_name)
return false;
return strcmp(ver_name, lib_ver) == 0;
}
/* For normal symbols, it is already in form of func@LIB_VER */
return strcmp(sym->name, name) == 0;
}
/* Transform symbol's virtual address (absolute for binaries and relative
* for shared libs) into file offset, which is what kernel is expecting
* for uprobe/uretprobe attachment.
* See Documentation/trace/uprobetracer.rst for more details. This is done
* by looking up symbol's containing section's header and using iter's virtual
* address (sh_addr) and corresponding file offset (sh_offset) to transform
* sym.st_value (virtual address) into desired final file offset.
*/
static unsigned long elf_sym_offset(struct elf_sym *sym)
{
return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
}
/* Find offset of function name in the provided ELF object. "binary_path" is
* the path to the ELF binary represented by "elf", and only used for error
* reporting matters. "name" matches symbol name or name@@LIB for library
* functions.
*/
long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
{
int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
const char *at_symbol, *lib_ver;
bool is_shared_lib;
long ret = -ENOENT;
size_t name_len;
GElf_Ehdr ehdr;
if (!gelf_getehdr(elf, &ehdr)) {
pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
}
/* for shared lib case, we do not need to calculate relative offset */
is_shared_lib = ehdr.e_type == ET_DYN;
/* Does name specify "@@LIB_VER" or "@LIB_VER" ? */
at_symbol = strchr(name, '@');
if (at_symbol) {
name_len = at_symbol - name;
/* skip second @ if it's @@LIB_VER case */
if (at_symbol[1] == '@')
at_symbol++;
lib_ver = at_symbol + 1;
} else {
name_len = strlen(name);
lib_ver = NULL;
}
/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
* a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
* linked binary may not have SHT_DYMSYM, so absence of a section should not be
* reported as a warning/error.
*/
for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
struct elf_sym_iter iter;
struct elf_sym *sym;
int last_bind = -1;
int cur_bind;
ret = elf_sym_iter_new(&iter, elf, binary_path, sh_types[i], STT_FUNC);
if (ret == -ENOENT)
continue;
if (ret)
goto out;
while ((sym = elf_sym_iter_next(&iter))) {
if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver))
continue;
cur_bind = GELF_ST_BIND(sym->sym.st_info);
if (ret > 0) {
/* handle multiple matches */
if (elf_sym_offset(sym) == ret) {
/* same offset, no problem */
continue;
} else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
/* Only accept one non-weak bind. */
pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
sym->name, name, binary_path);
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
} else if (cur_bind == STB_WEAK) {
/* already have a non-weak bind, and
* this is a weak bind, so ignore.
*/
continue;
}
}
ret = elf_sym_offset(sym);
last_bind = cur_bind;
}
if (ret > 0)
break;
}
if (ret > 0) {
pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
ret);
} else {
if (ret == 0) {
pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
is_shared_lib ? "should not be 0 in a shared library" :
"try using shared library path instead");
ret = -ENOENT;
} else {
pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
}
}
out:
return ret;
}
/* Find offset of function name in ELF object specified by path. "name" matches
* symbol name or name@@LIB for library functions.
*/
long elf_find_func_offset_from_file(const char *binary_path, const char *name)
{
struct elf_fd elf_fd;
long ret = -ENOENT;
ret = elf_open(binary_path, &elf_fd);
if (ret)
return ret;
ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
elf_close(&elf_fd);
return ret;
}
struct symbol {
const char *name;
int bind;
int idx;
};
static int symbol_cmp(const void *a, const void *b)
{
const struct symbol *sym_a = a;
const struct symbol *sym_b = b;
return strcmp(sym_a->name, sym_b->name);
}
/*
* Return offsets in @poffsets for symbols specified in @syms array argument.
* On success returns 0 and offsets are returned in allocated array with @cnt
* size, that needs to be released by the caller.
*/
int elf_resolve_syms_offsets(const char *binary_path, int cnt,
const char **syms, unsigned long **poffsets,
int st_type)
{
int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
int err = 0, i, cnt_done = 0;
unsigned long *offsets;
struct symbol *symbols;
struct elf_fd elf_fd;
err = elf_open(binary_path, &elf_fd);
if (err)
return err;
offsets = calloc(cnt, sizeof(*offsets));
symbols = calloc(cnt, sizeof(*symbols));
if (!offsets || !symbols) {
err = -ENOMEM;
goto out;
}
for (i = 0; i < cnt; i++) {
symbols[i].name = syms[i];
symbols[i].idx = i;
}
qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);
for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
struct elf_sym_iter iter;
struct elf_sym *sym;
err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], st_type);
if (err == -ENOENT)
continue;
if (err)
goto out;
while ((sym = elf_sym_iter_next(&iter))) {
unsigned long sym_offset = elf_sym_offset(sym);
int bind = GELF_ST_BIND(sym->sym.st_info);
struct symbol *found, tmp = {
.name = sym->name,
};
unsigned long *offset;
found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
if (!found)
continue;
offset = &offsets[found->idx];
if (*offset > 0) {
/* same offset, no problem */
if (*offset == sym_offset)
continue;
/* handle multiple matches */
if (found->bind != STB_WEAK && bind != STB_WEAK) {
/* Only accept one non-weak bind. */
pr_warn("elf: ambiguous match found '%s@%lu' in '%s' previous offset %lu\n",
sym->name, sym_offset, binary_path, *offset);
err = -ESRCH;
goto out;
} else if (bind == STB_WEAK) {
/* already have a non-weak bind, and
* this is a weak bind, so ignore.
*/
continue;
}
} else {
cnt_done++;
}
*offset = sym_offset;
found->bind = bind;
}
}
if (cnt != cnt_done) {
err = -ENOENT;
goto out;
}
*poffsets = offsets;
out:
free(symbols);
if (err)
free(offsets);
elf_close(&elf_fd);
return err;
}
/*
* Return offsets in @poffsets for symbols specified by @pattern argument.
* On success returns 0 and offsets are returned in allocated @poffsets
* array with the @pctn size, that needs to be released by the caller.
*/
int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
unsigned long **poffsets, size_t *pcnt)
{
int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM };
unsigned long *offsets = NULL;
size_t cap = 0, cnt = 0;
struct elf_fd elf_fd;
int err = 0, i;
err = elf_open(binary_path, &elf_fd);
if (err)
return err;
for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
struct elf_sym_iter iter;
struct elf_sym *sym;
err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
if (err == -ENOENT)
continue;
if (err)
goto out;
while ((sym = elf_sym_iter_next(&iter))) {
if (!glob_match(sym->name, pattern))
continue;
err = libbpf_ensure_mem((void **) &offsets, &cap, sizeof(*offsets),
cnt + 1);
if (err)
goto out;
offsets[cnt++] = elf_sym_offset(sym);
}
/* If we found anything in the first symbol section,
* do not search others to avoid duplicates.
*/
if (cnt)
break;
}
if (cnt) {
*poffsets = offsets;
*pcnt = cnt;
} else {
err = -ENOENT;
}
out:
if (err)
free(offsets);
elf_close(&elf_fd);
return err;
}
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