drm/nouveau: fix kernel-doc comments

[drm/drm-misc.git] / tools / lib / bpf / elf.c

// 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>
#include <linux/kernel.h>

#include "libbpf_internal.h"
#include "str_error.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))
                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,
                         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;
}