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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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#ifndef _GNU_SOURCE#define _GNU_SOURCE#endif#include <libelf.h>#include <gelf.h>#include <fcntl.h>#include <linux/kernel.h>
#include "libbpf_internal.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){ 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, errstr(ret)); 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) || !sh.sh_entsize) 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, (unsigned long)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;}