diff options
Diffstat (limited to 'tools/lib/bpf/elf.c')
| -rw-r--r-- | tools/lib/bpf/elf.c | 143 |
1 files changed, 131 insertions, 12 deletions
diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c index 9d0296c172..2a62bf411b 100644 --- a/tools/lib/bpf/elf.c +++ b/tools/lib/bpf/elf.c @@ -1,5 +1,8 @@ // 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> @@ -10,6 +13,17 @@ #define STRERR_BUFSIZE 128 +/* 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]; @@ -64,13 +78,18 @@ 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; @@ -111,6 +130,27 @@ static int elf_sym_iter_new(struct elf_sym_iter *iter, 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; } @@ -119,6 +159,7 @@ 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; @@ -138,12 +179,83 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter) 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 @@ -166,7 +278,8 @@ static unsigned long elf_sym_offset(struct elf_sym *sym) 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; + const char *at_symbol, *lib_ver; + bool is_shared_lib; long ret = -ENOENT; size_t name_len; GElf_Ehdr ehdr; @@ -179,9 +292,18 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) /* 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; + /* 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 @@ -201,20 +323,17 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) goto out; while ((sym = elf_sym_iter_next(&iter))) { - /* User can specify func, func@@LIB or func@@LIB_VERSION. */ - if (strncmp(sym->name, 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 && sym->name[name_len] != '\0' && sym->name[name_len] != '@') + 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 (last_bind != STB_WEAK && cur_bind != STB_WEAK) { + 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); |