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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: 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
committed by
Andrii Nakryiko
Andrii Nakryiko
parent
a1c2e05c4f
commit
0cd5b05f53
197
src/elf.c
Normal file
197
src/elf.c
Normal file
@@ -0,0 +1,197 @@
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// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
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#include <libelf.h>
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#include <gelf.h>
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#include <fcntl.h>
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#include <linux/kernel.h>
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#include "libbpf_internal.h"
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#include "str_error.h"
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#define STRERR_BUFSIZE 128
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/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
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static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
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{
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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GElf_Shdr sh;
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if (!gelf_getshdr(scn, &sh))
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continue;
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if (sh.sh_type == sh_type)
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return scn;
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}
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return NULL;
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}
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/* Find offset of function name in the provided ELF object. "binary_path" is
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* the path to the ELF binary represented by "elf", and only used for error
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* reporting matters. "name" matches symbol name or name@@LIB for library
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* functions.
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*/
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long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
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{
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int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
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bool is_shared_lib, is_name_qualified;
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long ret = -ENOENT;
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size_t name_len;
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GElf_Ehdr ehdr;
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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}
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/* for shared lib case, we do not need to calculate relative offset */
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is_shared_lib = ehdr.e_type == ET_DYN;
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name_len = strlen(name);
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/* Does name specify "@@LIB"? */
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is_name_qualified = strstr(name, "@@") != NULL;
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/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
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* a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
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* linked binary may not have SHT_DYMSYM, so absence of a section should not be
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* reported as a warning/error.
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*/
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for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
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size_t nr_syms, strtabidx, idx;
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Elf_Data *symbols = NULL;
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Elf_Scn *scn = NULL;
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int last_bind = -1;
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const char *sname;
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GElf_Shdr sh;
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scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
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if (!scn) {
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pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
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binary_path);
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continue;
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}
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if (!gelf_getshdr(scn, &sh))
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continue;
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strtabidx = sh.sh_link;
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symbols = elf_getdata(scn, 0);
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if (!symbols) {
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pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
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binary_path, elf_errmsg(-1));
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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}
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nr_syms = symbols->d_size / sh.sh_entsize;
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for (idx = 0; idx < nr_syms; idx++) {
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int curr_bind;
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GElf_Sym sym;
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Elf_Scn *sym_scn;
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GElf_Shdr sym_sh;
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if (!gelf_getsym(symbols, idx, &sym))
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continue;
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if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
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continue;
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sname = elf_strptr(elf, strtabidx, sym.st_name);
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if (!sname)
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continue;
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curr_bind = GELF_ST_BIND(sym.st_info);
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/* User can specify func, func@@LIB or func@@LIB_VERSION. */
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if (strncmp(sname, name, name_len) != 0)
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continue;
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/* ...but we don't want a search for "foo" to match 'foo2" also, so any
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* additional characters in sname should be of the form "@@LIB".
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*/
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if (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
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continue;
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if (ret >= 0) {
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/* handle multiple matches */
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if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
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/* Only accept one non-weak bind. */
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pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
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sname, name, binary_path);
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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} else if (curr_bind == STB_WEAK) {
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/* already have a non-weak bind, and
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* this is a weak bind, so ignore.
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*/
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continue;
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}
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}
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/* Transform symbol's virtual address (absolute for
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* binaries and relative for shared libs) into file
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* offset, which is what kernel is expecting for
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* uprobe/uretprobe attachment.
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* See Documentation/trace/uprobetracer.rst for more
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* details.
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* This is done by looking up symbol's containing
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* section's header and using it's virtual address
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* (sh_addr) and corresponding file offset (sh_offset)
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* to transform sym.st_value (virtual address) into
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* desired final file offset.
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*/
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sym_scn = elf_getscn(elf, sym.st_shndx);
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if (!sym_scn)
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continue;
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if (!gelf_getshdr(sym_scn, &sym_sh))
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continue;
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ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
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last_bind = curr_bind;
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}
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if (ret > 0)
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break;
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}
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if (ret > 0) {
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pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
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ret);
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} else {
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if (ret == 0) {
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pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
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is_shared_lib ? "should not be 0 in a shared library" :
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"try using shared library path instead");
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ret = -ENOENT;
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} else {
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pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
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}
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}
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out:
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return ret;
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}
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/* Find offset of function name in ELF object specified by path. "name" matches
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* symbol name or name@@LIB for library functions.
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*/
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long elf_find_func_offset_from_file(const char *binary_path, const char *name)
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{
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char errmsg[STRERR_BUFSIZE];
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long ret = -ENOENT;
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Elf *elf;
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int fd;
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fd = open(binary_path, O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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ret = -errno;
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pr_warn("failed to open %s: %s\n", binary_path,
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libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
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return ret;
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}
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elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
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if (!elf) {
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pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
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close(fd);
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return -LIBBPF_ERRNO__FORMAT;
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}
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ret = elf_find_func_offset(elf, binary_path, name);
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elf_end(elf);
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close(fd);
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return ret;
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}
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185
src/libbpf.c
185
src/libbpf.c
@@ -11004,191 +11004,6 @@ err_clean_legacy:
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return err;
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return err;
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}
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}
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/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
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static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
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{
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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GElf_Shdr sh;
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if (!gelf_getshdr(scn, &sh))
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continue;
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if (sh.sh_type == sh_type)
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return scn;
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}
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return NULL;
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}
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/* Find offset of function name in the provided ELF object. "binary_path" is
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* the path to the ELF binary represented by "elf", and only used for error
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* reporting matters. "name" matches symbol name or name@@LIB for library
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* functions.
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*/
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static long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
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{
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int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
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bool is_shared_lib, is_name_qualified;
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long ret = -ENOENT;
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size_t name_len;
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GElf_Ehdr ehdr;
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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}
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/* for shared lib case, we do not need to calculate relative offset */
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is_shared_lib = ehdr.e_type == ET_DYN;
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name_len = strlen(name);
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/* Does name specify "@@LIB"? */
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is_name_qualified = strstr(name, "@@") != NULL;
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/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
|
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* a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
|
|
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* linked binary may not have SHT_DYMSYM, so absence of a section should not be
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* reported as a warning/error.
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*/
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for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
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size_t nr_syms, strtabidx, idx;
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Elf_Data *symbols = NULL;
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Elf_Scn *scn = NULL;
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int last_bind = -1;
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const char *sname;
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GElf_Shdr sh;
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scn = elf_find_next_scn_by_type(elf, sh_types[i], NULL);
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if (!scn) {
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pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
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binary_path);
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continue;
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}
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if (!gelf_getshdr(scn, &sh))
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continue;
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strtabidx = sh.sh_link;
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symbols = elf_getdata(scn, 0);
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if (!symbols) {
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pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
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binary_path, elf_errmsg(-1));
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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}
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nr_syms = symbols->d_size / sh.sh_entsize;
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for (idx = 0; idx < nr_syms; idx++) {
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int curr_bind;
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GElf_Sym sym;
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Elf_Scn *sym_scn;
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GElf_Shdr sym_sh;
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if (!gelf_getsym(symbols, idx, &sym))
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continue;
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if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
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continue;
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sname = elf_strptr(elf, strtabidx, sym.st_name);
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if (!sname)
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continue;
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curr_bind = GELF_ST_BIND(sym.st_info);
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|
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/* User can specify func, func@@LIB or func@@LIB_VERSION. */
|
|
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if (strncmp(sname, name, name_len) != 0)
|
|
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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".
|
|
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*/
|
|
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if (!is_name_qualified && sname[name_len] != '\0' && sname[name_len] != '@')
|
|
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continue;
|
|
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|
|
||||||
if (ret >= 0) {
|
|
||||||
/* handle multiple matches */
|
|
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if (last_bind != STB_WEAK && curr_bind != STB_WEAK) {
|
|
||||||
/* Only accept one non-weak bind. */
|
|
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pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
|
|
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sname, name, binary_path);
|
|
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ret = -LIBBPF_ERRNO__FORMAT;
|
|
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goto out;
|
|
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} 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);
|
|
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if (!sym_scn)
|
|
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continue;
|
|
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if (!gelf_getshdr(sym_scn, &sym_sh))
|
|
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continue;
|
|
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|
|
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ret = sym.st_value - sym_sh.sh_addr + sym_sh.sh_offset;
|
|
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last_bind = curr_bind;
|
|
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}
|
|
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if (ret > 0)
|
|
||||||
break;
|
|
||||||
}
|
|
||||||
|
|
||||||
if (ret > 0) {
|
|
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pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
|
|
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ret);
|
|
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} else {
|
|
||||||
if (ret == 0) {
|
|
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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);
|
|
||||||
}
|
|
||||||
}
|
|
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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
|
/* Find offset of function name in archive specified by path. Currently
|
||||||
* supported are .zip files that do not compress their contents, as used on
|
* 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
|
* Android in the form of APKs, for example. "file_name" is the name of the ELF
|
||||||
|
|||||||
@@ -15,6 +15,7 @@
|
|||||||
#include <linux/err.h>
|
#include <linux/err.h>
|
||||||
#include <fcntl.h>
|
#include <fcntl.h>
|
||||||
#include <unistd.h>
|
#include <unistd.h>
|
||||||
|
#include <libelf.h>
|
||||||
#include "relo_core.h"
|
#include "relo_core.h"
|
||||||
|
|
||||||
/* make sure libbpf doesn't use kernel-only integer typedefs */
|
/* 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
|
#define PROG_LOAD_ATTEMPTS 5
|
||||||
int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts);
|
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 */
|
#endif /* __LIBBPF_LIBBPF_INTERNAL_H */
|
||||||
|
|||||||
Reference in New Issue
Block a user