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Code Issues Releases Wiki Activity

libbpf: Move elf_find_func_offset* functions to elf object

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Adding new elf object that will contain elf related functions.
There's no functional change.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230809083440.3209381-9-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jiri Olsa 2023-08-09 10:34:20 +02:00 committed by Alexei Starovoitov
parent 8097e460ca
commit 5c74272504
4 changed files with 202 additions and 186 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
tools/lib/bpf/Build
View file

@ -1,4 +1,4 @@
libbpf-y := libbpf.o bpf.o nlattr.o btf.o libbpf_errno.o str_error.o \
netlink.o bpf_prog_linfo.o libbpf_probes.o hashmap.o \
btf_dump.o ringbuf.o strset.o linker.o gen_loader.o relo_core.o \
usdt.o zip.o
usdt.o zip.o elf.o

197
tools/lib/bpf/elf.c Normal file
View file

@ -0,0 +1,197 @@
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
#include <linux/kernel.h>
#include "libbpf_internal.h"
#include "str_error.h"
#define STRERR_BUFSIZE 128
/* 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;
}
/* 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 };
bool is_shared_lib, is_name_qualified;
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;
name_len = strlen(name);
/* Does name specify "@@LIB"? */
is_name_qualified = strstr(name, "@@") != 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++) {
size_t nr_syms, strtabidx, idx;
Elf_Data *symbols = NULL;
Elf_Scn *scn = NULL;
int last_bind = -1;
const char *sname;
GElf_Shdr sh;
scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
if (!scn) {
pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
binary_path);
continue;
}
if (!gelf_getshdr(scn, &sh))
continue;
strtabidx = sh.sh_link;
symbols = elf_getdata(scn, 0);
if (!symbols) {
pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
binary_path, elf_errmsg(-1));
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
}
nr_syms = symbols->d_size / sh.sh_entsize;
for (idx = 0; idx < nr_syms; idx++) {
int curr_bind;
GElf_Sym sym;
Elf_Scn *sym_scn;
GElf_Shdr sym_sh;
if (!gelf_getsym(symbols, idx, &sym))
continue;
if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
continue;
sname = elf_strptr(elf, strtabidx, sym.st_name);
if (!sname)
continue;
curr_bind = GELF_ST_BIND(sym.st_info);
/* User can specify func, func@@LIB or func@@LIB_VERSION. */
if (strncmp(sname, name, name_len) != 0)
continue;
/* ...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 (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
continue;
if (ret >= 0) {
/* handle multiple matches */
if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
/* Only accept one non-weak bind. */
pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
sname, name, binary_path);
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
} else if (curr_bind == STB_WEAK) {
/* already have a non-weak bind, and
* this is a weak bind, so ignore.
*/
continue;
}
}
/* 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 it's virtual address
* (sh_addr) and corresponding file offset (sh_offset)
* to transform sym.st_value (virtual address) into
* desired final file offset.
*/
sym_scn = elf_getscn(elf, sym.st_shndx);
if (!sym_scn)
continue;
if (!gelf_getshdr(sym_scn, &sym_sh))
continue;
ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
last_bind = curr_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)
{
char errmsg[STRERR_BUFSIZE];
long ret = -ENOENT;
Elf *elf;
int fd;
fd = open(binary_path, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = -errno;
pr_warn("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;
}
ret = elf_find_func_offset(elf, binary_path, name);
elf_end(elf);
close(fd);
return ret;
}

185
tools/lib/bpf/libbpf.c
View file

@ -11004,191 +11004,6 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe,
return err;
}
/* 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;
}
/* 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.
*/
static long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
{
int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
bool is_shared_lib, is_name_qualified;
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;
name_len = strlen(name);
/* Does name specify "@@LIB"? */
is_name_qualified = strstr(name, "@@") != 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++) {
size_t nr_syms, strtabidx, idx;
Elf_Data *symbols = NULL;
Elf_Scn *scn = NULL;
int last_bind = -1;
const char *sname;
GElf_Shdr sh;
scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
if (!scn) {
pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
binary_path);
continue;
}
if (!gelf_getshdr(scn, &sh))
continue;
strtabidx = sh.sh_link;
symbols = elf_getdata(scn, 0);
if (!symbols) {
pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
binary_path, elf_errmsg(-1));
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
}
nr_syms = symbols->d_size / sh.sh_entsize;
for (idx = 0; idx < nr_syms; idx++) {
int curr_bind;
GElf_Sym sym;
Elf_Scn *sym_scn;
GElf_Shdr sym_sh;
if (!gelf_getsym(symbols, idx, &sym))
continue;
if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
continue;
sname = elf_strptr(elf, strtabidx, sym.st_name);
if (!sname)
continue;
curr_bind = GELF_ST_BIND(sym.st_info);
/* User can specify func, func@@LIB or func@@LIB_VERSION. */
if (strncmp(sname, name, name_len) != 0)
continue;
/* ...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 (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
continue;
if (ret >= 0) {
/* handle multiple matches */
if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
/* Only accept one non-weak bind. */
pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
sname, name, binary_path);
ret = -LIBBPF_ERRNO__FORMAT;
goto out;
} else if (curr_bind == STB_WEAK) {
/* already have a non-weak bind, and
* this is a weak bind, so ignore.
*/
continue;
}
}
/* 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 it's virtual address
* (sh_addr) and corresponding file offset (sh_offset)
* to transform sym.st_value (virtual address) into
* desired final file offset.
*/
sym_scn = elf_getscn(elf, sym.st_shndx);
if (!sym_scn)
continue;
if (!gelf_getshdr(sym_scn, &sym_sh))
continue;
ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
last_bind = curr_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.
*/
static long elf_find_func_offset_from_file(const char *binary_path, const char *name)
{
char errmsg[STRERR_BUFSIZE];
long ret = -ENOENT;
Elf *elf;
int fd;
fd = open(binary_path, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = -errno;
pr_warn("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;
}
ret = elf_find_func_offset(elf, binary_path, name);
elf_end(elf);
close(fd);
return ret;
}
/* Find offset of function name in archive specified by path. Currently
* supported are .zip files that do not compress their contents, as used on
* Android in the form of APKs, for example. "file_name" is the name of the ELF

4
tools/lib/bpf/libbpf_internal.h
View file

@ -15,6 +15,7 @@
#include <linux/err.h>
#include <fcntl.h>
#include <unistd.h>
#include <libelf.h>
#include "relo_core.h"
/* make sure libbpf doesn't use kernel-only integer typedefs */
@ -577,4 +578,7 @@ static inline bool is_pow_of_2(size_t x)
#define PROG_LOAD_ATTEMPTS 5
int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts);
long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name);
long elf_find_func_offset_from_file(const char *binary_path, const char *name);
#endif /* __LIBBPF_LIBBPF_INTERNAL_H */