Commit 5c742725 authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

libbpf: Move elf_find_func_offset* functions to elf object 



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

Suggested-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230809083440.3209381-9-jolsa@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 8097e460

tools/lib/bpf/Build

+1 −1
Original line number Diff line number Diff line 
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

tools/lib/bpf/elf.c

0 → 100644
+197 −0
Original line number Diff line number Diff line 
// 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;

}

tools/lib/bpf/libbpf.c

+0 −185
Original line number Diff line number Diff line
@@ -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

tools/lib/bpf/libbpf_internal.h

+4 −0
Original line number Diff line number Diff line
@@ -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 */