// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/*
* BPF static linker
*
* Copyright (c) 2021 Facebook
*/
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <linux/err.h>
#include <linux/btf.h>
#include <elf.h>
#include <libelf.h>
#include <fcntl.h>
#include "libbpf.h"
#include "btf.h"
#include "libbpf_internal.h"
#include "strset.h"
#define BTF_EXTERN_SEC ".extern"
struct src_sec {
const char *sec_name;
/* positional (not necessarily ELF) index in an array of sections */
int id;
/* positional (not necessarily ELF) index of a matching section in a final object file */
int dst_id;
/* section data offset in a matching output section */
int dst_off;
/* whether section is omitted from the final ELF file */
bool skipped;
/* whether section is an ephemeral section, not mapped to an ELF section */
bool ephemeral;
/* ELF info */
size_t sec_idx;
Elf_Scn *scn;
Elf64_Shdr *shdr;
Elf_Data *data;
/* corresponding BTF DATASEC type ID */
int sec_type_id;
};
struct src_obj {
const char *filename;
int fd;
Elf *elf;
/* Section header strings section index */
size_t shstrs_sec_idx;
/* SYMTAB section index */
size_t symtab_sec_idx;
struct btf *btf;
struct btf_ext *btf_ext;
/* List of sections (including ephemeral). Slot zero is unused. */
struct src_sec *secs;
int sec_cnt;
/* mapping of symbol indices from src to dst ELF */
int *sym_map;
/* mapping from the src BTF type IDs to dst ones */
int *btf_type_map;
};
/* single .BTF.ext data section */
struct btf_ext_sec_data {
size_t rec_cnt;
__u32 rec_sz;
void *recs;
};
struct glob_sym {
/* ELF symbol index */
int sym_idx;
/* associated section id for .ksyms, .kconfig, etc, but not .extern */
int sec_id;
/* extern name offset in STRTAB */
int name_off;
/* optional associated BTF type ID */
int btf_id;
/* BTF type ID to which VAR/FUNC type is pointing to; used for
* rewriting types when extern VAR/FUNC is resolved to a concrete
* definition
*/
int underlying_btf_id;
/* sec_var index in the corresponding dst_sec, if exists */
int var_idx;
/* extern or resolved/global symbol */
bool is_extern;
/* weak or strong symbol, never goes back from strong to weak */
bool is_weak;
};
struct dst_sec {
char *sec_name;
/* positional (not necessarily ELF) index in an array of sections */
int id;
bool ephemeral;
/* ELF info */
size_t sec_idx;
Elf_Scn *scn;
Elf64_Shdr *shdr;
Elf_Data *data;
/* final output section size */
int sec_sz;
/* final output contents of the section */
void *raw_data;
/* corresponding STT_SECTION symbol index in SYMTAB */
int sec_sym_idx;
/* section's DATASEC variable info, emitted on BTF finalization */
bool has_btf;
int sec_var_cnt;
struct btf_var_secinfo *sec_vars;
/* section's .BTF.ext data */
struct btf_ext_sec_data func_info;
struct btf_ext_sec_data line_info;
struct btf_ext_sec_data core_relo_info;
};
struct bpf_linker {
char *filename;
int fd;
Elf *elf;
Elf64_Ehdr *elf_hdr;
/* Output sections metadata */
struct dst_sec *secs;
int sec_cnt;
struct strset *strtab_strs; /* STRTAB unique strings */
size_t strtab_sec_idx; /* STRTAB section index */
size_t symtab_sec_idx; /* SYMTAB section index */
struct btf *btf;
struct btf_ext *btf_ext;
/* global (including extern) ELF symbols */
int glob_sym_cnt;
struct glob_sym *glob_syms;
};
#define pr_warn_elf(fmt, ...) \
libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1))
static int init_output_elf(struct bpf_linker *linker, const char *file);
static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
const struct bpf_linker_file_opts *opts,
struct src_obj *obj);
static int linker_sanity_check_elf(struct src_obj *obj);
static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
static int linker_sanity_check_btf(struct src_obj *obj);
static int linker_sanity_check_btf_ext(struct src_obj *obj);
static int linker_fixup_btf(struct src_obj *obj);
static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj);
static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj);
static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
Elf64_Sym *sym, const char *sym_name, int src_sym_idx);
static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj);
static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj);
static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj);
static int finalize_btf(struct bpf_linker *linker);
static int finalize_btf_ext(struct bpf_linker *linker);
void bpf_linker__free(struct bpf_linker *linker)
{
int i;
if (!linker)
return;
free(linker->filename);
if (linker->elf)
elf_end(linker->elf);
if (linker->fd >= 0)
close(linker->fd);
strset__free(linker->strtab_strs);
btf__free(linker->btf);
btf_ext__free(linker->btf_ext);
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
free(sec->sec_name);
free(sec->raw_data);
free(sec->sec_vars);
free(sec->func_info.recs);
free(sec->line_info.recs);
free(sec->core_relo_info.recs);
}
free(linker->secs);
free(linker->glob_syms);
free(linker);
}
struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts)
{
struct bpf_linker *linker;
int err;
if (!OPTS_VALID(opts, bpf_linker_opts))
return errno = EINVAL, NULL;
if (elf_version(EV_CURRENT) == EV_NONE) {
pr_warn_elf("libelf initialization failed");
return errno = EINVAL, NULL;
}
linker = calloc(1, sizeof(*linker));
if (!linker)
return errno = ENOMEM, NULL;
linker->fd = -1;
err = init_output_elf(linker, filename);
if (err)
goto err_out;
return linker;
err_out:
bpf_linker__free(linker);
return errno = -err, NULL;
}
static struct dst_sec *add_dst_sec(struct bpf_linker *linker, const char *sec_name)
{
struct dst_sec *secs = linker->secs, *sec;
size_t new_cnt = linker->sec_cnt ? linker->sec_cnt + 1 : 2;
secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
if (!secs)
return NULL;
/* zero out newly allocated memory */
memset(secs + linker->sec_cnt, 0, (new_cnt - linker->sec_cnt) * sizeof(*secs));
linker->secs = secs;
linker->sec_cnt = new_cnt;
sec = &linker->secs[new_cnt - 1];
sec->id = new_cnt - 1;
sec->sec_name = strdup(sec_name);
if (!sec->sec_name)
return NULL;
return sec;
}
static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx)
{
struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
Elf64_Sym *syms, *sym;
size_t sym_cnt = symtab->sec_sz / sizeof(*sym);
syms = libbpf_reallocarray(symtab->raw_data, sym_cnt + 1, sizeof(*sym));
if (!syms)
return NULL;
sym = &syms[sym_cnt];
memset(sym, 0, sizeof(*sym));
symtab->raw_data = syms;
symtab->sec_sz += sizeof(*sym);
symtab->shdr->sh_size += sizeof(*sym);
symtab->data->d_size += sizeof(*sym);
if (sym_idx)
*sym_idx = sym_cnt;
return sym;
}
static int init_output_elf(struct bpf_linker *linker, const char *file)
{
int err, str_off;
Elf64_Sym *init_sym;
struct dst_sec *sec;
linker->filename = strdup(file);
if (!linker->filename)
return -ENOMEM;
linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
if (linker->fd < 0) {
err = -errno;
pr_warn("failed to create '%s': %d\n", file, err);
return err;
}
linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
if (!linker->elf) {
pr_warn_elf("failed to create ELF object");
return -EINVAL;
}
/* ELF header */
linker->elf_hdr = elf64_newehdr(linker->elf);
if (!linker->elf_hdr) {
pr_warn_elf("failed to create ELF header");
return -EINVAL;
}
linker->elf_hdr->e_machine = EM_BPF;
linker->elf_hdr->e_type = ET_REL;
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
#else
#error "Unknown __BYTE_ORDER__"
#endif
/* STRTAB */
/* initialize strset with an empty string to conform to ELF */
linker->strtab_strs = strset__new(INT_MAX, "", sizeof(""));
if (libbpf_get_error(linker->strtab_strs))
return libbpf_get_error(linker->strtab_strs);
sec = add_dst_sec(linker, ".strtab");
if (!sec)
return -ENOMEM;
sec->scn = elf_newscn(linker->elf);
if (!sec->scn) {
pr_warn_elf("failed to create STRTAB section");
return -EINVAL;
}
sec->shdr = elf64_getshdr(sec->scn);
if (!sec->shdr)
return -EINVAL;
sec->data = elf_newdata(sec->scn);
if (!sec->data) {
pr_warn_elf("failed to create STRTAB data");
return -EINVAL;
}
str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
if (str_off < 0)
return str_off;
sec->sec_idx = elf_ndxscn(sec->scn);
linker->elf_hdr->e_shstrndx = sec->sec_idx;
linker->strtab_sec_idx = sec->sec_idx;
sec->shdr->sh_name = str_off;
sec->shdr->sh_type = SHT_STRTAB;
sec->shdr->sh_flags = SHF_STRINGS;
sec->shdr->sh_offset = 0;
sec->shdr->sh_link = 0;
sec->shdr->sh_info = 0;
sec->shdr->sh_addralign = 1;
sec->shdr->sh_size = sec->sec_sz = 0;
sec->shdr->sh_entsize = 0;
/* SYMTAB */
sec = add_dst_sec(linker, ".symtab");
if (!sec)
return -ENOMEM;
sec->scn = elf_newscn(linker->elf);
if (!sec->scn) {
pr_warn_elf("failed to create SYMTAB section");
return -EINVAL;
}
sec->shdr = elf64_getshdr(sec->scn);
if (!sec->shdr)
return -EINVAL;
sec->data = elf_newdata(sec->scn);
if (!sec->data) {
pr_warn_elf("failed to create SYMTAB data");
return -EINVAL;
}
str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
if (str_off < 0)
return str_off;
sec->sec_idx = elf_ndxscn(sec->scn);
linker->symtab_sec_idx = sec->sec_idx;
sec->shdr->sh_name = str_off;
sec->shdr->sh_type = SHT_SYMTAB;
sec->shdr->sh_flags = 0;
sec->shdr->sh_offset = 0;
sec->shdr->sh_link = linker->strtab_sec_idx;
/* sh_info should be one greater than the index of the last local
* symbol (i.e., binding is STB_LOCAL). But why and who cares?
*/
sec->shdr->sh_info = 0;
sec->shdr->sh_addralign = 8;
sec->shdr->sh_entsize = sizeof(Elf64_Sym);
/* .BTF */
linker->btf = btf__new_empty();
err = libbpf_get_error(linker->btf);
if (err)
return err;
/* add the special all-zero symbol */
init_sym = add_new_sym(linker, NULL);
if (!init_sym)
return -EINVAL;
init_sym->st_name = 0;
init_sym->st_info = 0;
init_sym->st_other = 0;
init_sym->st_shndx = SHN_UNDEF;
init_sym->st_value = 0;
init_sym->st_size = 0;
return 0;
}
int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
const struct bpf_linker_file_opts *opts)
{
struct src_obj obj = {};
int err = 0;
if (!OPTS_VALID(opts, bpf_linker_file_opts))
return libbpf_err(-EINVAL);
if (!linker->elf)
return libbpf_err(-EINVAL);
err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
err = err ?: linker_append_sec_data(linker, &obj);
err = err ?: linker_append_elf_syms(linker, &obj);
err = err ?: linker_append_elf_relos(linker, &obj);
err = err ?: linker_append_btf(linker, &obj);
err = err ?: linker_append_btf_ext(linker, &obj);
/* free up src_obj resources */
free(obj.btf_type_map);
btf__free(obj.btf);
btf_ext__free(obj.btf_ext);
free(obj.secs);
free(obj.sym_map);
if (obj.elf)
elf_end(obj.elf);
if (obj.fd >= 0)
close(obj.fd);
return libbpf_err(err);
}
static bool is_dwarf_sec_name(const char *name)
{
/* approximation, but the actual list is too long */
return strncmp(name, ".debug_", sizeof(".debug_") - 1) == 0;
}
static bool is_ignored_sec(struct src_sec *sec)
{
Elf64_Shdr *shdr = sec->shdr;
const char *name = sec->sec_name;
/* no special handling of .strtab */
if (shdr->sh_type == SHT_STRTAB)
return true;
/* ignore .llvm_addrsig section as well */
if (shdr->sh_type == SHT_LLVM_ADDRSIG)
return true;
/* no subprograms will lead to an empty .text section, ignore it */
if (shdr->sh_type == SHT_PROGBITS && shdr->sh_size == 0 &&
strcmp(sec->sec_name, ".text") == 0)
return true;
/* DWARF sections */
if (is_dwarf_sec_name(sec->sec_name))
return true;
if (strncmp(name, ".rel", sizeof(".rel") - 1) == 0) {
name += sizeof(".rel") - 1;
/* DWARF section relocations */
if (is_dwarf_sec_name(name))
return true;
/* .BTF and .BTF.ext don't need relocations */
if (strcmp(name, BTF_ELF_SEC) == 0 ||
strcmp(name, BTF_EXT_ELF_SEC) == 0)
return true;
}
return false;
}
static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
{
struct src_sec *secs = obj->secs, *sec;
size_t new_cnt = obj->sec_cnt ? obj->sec_cnt + 1 : 2;
secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
if (!secs)
return NULL;
/* zero out newly allocated memory */
memset(secs + obj->sec_cnt, 0, (new_cnt - obj->sec_cnt) * sizeof(*secs));
obj->secs = secs;
obj->sec_cnt = new_cnt;
sec = &obj->secs[new_cnt - 1];
sec->id = new_cnt - 1;
sec->sec_name = sec_name;
return sec;
}
static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
const struct bpf_linker_file_opts *opts,
struct src_obj *obj)
{
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
const int host_endianness = ELFDATA2LSB;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
const int host_endianness = ELFDATA2MSB;
#else
#error "Unknown __BYTE_ORDER__"
#endif
int err = 0;
Elf_Scn *scn;
Elf_Data *data;
Elf64_Ehdr *ehdr;
Elf64_Shdr *shdr;
struct src_sec *sec;
pr_debug("linker: adding object file '%s'...\n", filename);
obj->filename = filename;
obj->fd = open(filename, O_RDONLY | O_CLOEXEC);
if (obj->fd < 0) {
err = -errno;
pr_warn("failed to open file '%s': %d\n", filename, err);
return err;
}
obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL);
if (!obj->elf) {
err = -errno;
pr_warn_elf("failed to parse ELF file '%s'", filename);
return err;
}
/* Sanity check ELF file high-level properties */
ehdr = elf64_getehdr(obj->elf);
if (!ehdr) {
err = -errno;
pr_warn_elf("failed to get ELF header for %s", filename);
return err;
}
if (ehdr->e_ident[EI_DATA] != host_endianness) {
err = -EOPNOTSUPP;
pr_warn_elf("unsupported byte order of ELF file %s", filename);
return err;
}
if (ehdr->e_type != ET_REL
|| ehdr->e_machine != EM_BPF
|| ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
err = -EOPNOTSUPP;
pr_warn_elf("unsupported kind of ELF file %s", filename);
return err;
}
if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) {
err = -errno;
pr_warn_elf("failed to get SHSTRTAB section index for %s", filename);
return err;
}
scn = NULL;
while ((scn = elf_nextscn(obj->elf, scn)) != NULL) {
size_t sec_idx = elf_ndxscn(scn);
const char *sec_name;
shdr = elf64_getshdr(scn);
if (!shdr) {
err = -errno;
pr_warn_elf("failed to get section #%zu header for %s",
sec_idx, filename);
return err;
}
sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name);
if (!sec_name) {
err = -errno;
pr_warn_elf("failed to get section #%zu name for %s",
sec_idx, filename);
return err;
}
data = elf_getdata(scn, 0);
if (!data) {
err = -errno;
pr_warn_elf("failed to get section #%zu (%s) data from %s",
sec_idx, sec_name, filename);
return err;
}
sec = add_src_sec(obj, sec_name);
if (!sec)
return -ENOMEM;
sec->scn = scn;
sec->shdr = shdr;
sec->data = data;
sec->sec_idx = elf_ndxscn(scn);
if (is_ignored_sec(sec)) {
sec->skipped = true;
continue;
}
switch (shdr->sh_type) {
case SHT_SYMTAB:
if (obj->symtab_sec_idx) {
err = -EOPNOTSUPP;
pr_warn("multiple SYMTAB sections found, not supported\n");
return err;
}
obj->symtab_sec_idx = sec_idx;
break;
case SHT_STRTAB:
/* we'll construct our own string table */
break;
case SHT_PROGBITS:
if (strcmp(sec_name, BTF_ELF_SEC) == 0) {
obj->btf = btf__new(data->d_buf, shdr->sh_size);
err = libbpf_get_error(obj->btf);
if (err) {
pr_warn("failed to parse .BTF from %s: %d\n", filename, err);
return err;
}
sec->skipped = true;
continue;
}
if (strcmp(sec_name, BTF_EXT_ELF_SEC) == 0) {
obj->btf_ext = btf_ext__new(data->d_buf, shdr->sh_size);
err = libbpf_get_error(obj->btf_ext);
if (err) {
pr_warn("failed to parse .BTF.ext from '%s': %d\n", filename, err);
return err;
}
sec->skipped = true;
continue;
}
/* data & code */
break;
case SHT_NOBITS:
/* BSS */
break;
case SHT_REL:
/* relocations */
break;
default:
pr_warn("unrecognized section #%zu (%s) in %s\n",
sec_idx, sec_name, filename);
err = -EINVAL;
return err;
}
}
err = err ?: linker_sanity_check_elf(obj);
err = err ?: linker_sanity_check_btf(obj);
err = err ?: linker_sanity_check_btf_ext(obj);
err = err ?: linker_fixup_btf(obj);
return err;
}
static int linker_sanity_check_elf(struct src_obj *obj)
{
struct src_sec *sec;
int i, err;
if (!obj->symtab_sec_idx) {
pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
return -EINVAL;
}
if (!obj->shstrs_sec_idx) {
pr_warn("ELF is missing section headers STRTAB section in %s\n", obj->filename);
return -EINVAL;
}
for (i = 1; i < obj->sec_cnt; i++) {
sec = &obj->secs[i];
if (sec->sec_name[0] == '\0') {
pr_warn("ELF section #%zu has empty name in %s\n", sec->sec_idx, obj->filename);
return -EINVAL;
}
if (is_dwarf_sec_name(sec->sec_name))
continue;
if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign)) {
pr_warn("ELF section #%zu alignment %llu is non pow-of-2 alignment in %s\n",
sec->sec_idx, (long long unsigned)sec->shdr->sh_addralign,
obj->filename);
return -EINVAL;
}
if (sec->shdr->sh_addralign != sec->data->d_align) {
pr_warn("ELF section #%zu has inconsistent alignment addr=%llu != d=%llu in %s\n",
sec->sec_idx, (long long unsigned)sec->shdr->sh_addralign,
(long long unsigned)sec->data->d_align, obj->filename);
return -EINVAL;
}
if (sec->shdr->sh_size != sec->data->d_size) {
pr_warn("ELF section #%zu has inconsistent section size sh=%llu != d=%llu in %s\n",
sec->sec_idx, (long long unsigned)sec->shdr->sh_size,
(long long unsigned)sec->data->d_size, obj->filename);
return -EINVAL;
}
switch (sec->shdr->sh_type) {
case SHT_SYMTAB:
err = linker_sanity_check_elf_symtab(obj, sec);
if (err)
return err;
break;
case SHT_STRTAB:
break;
case SHT_PROGBITS:
if (sec->shdr->sh_flags & SHF_EXECINSTR) {
if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0) {
pr_warn("ELF section #%zu has unexpected size alignment %llu in %s\n",
sec->sec_idx, (long long unsigned)sec->shdr->sh_size,
obj->filename);
return -EINVAL;
}
}
break;
case SHT_NOBITS:
break;
case SHT_REL:
err = linker_sanity_check_elf_relos(obj, sec);
if (err)
return err;
break;
case SHT_LLVM_ADDRSIG:
break;
default:
pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
return -EINVAL;
}
}
return 0;
}
static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
{
struct src_sec *link_sec;
Elf64_Sym *sym;
int i, n;
if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
return -EINVAL;
if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
return -EINVAL;
if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
return -EINVAL;
}
link_sec = &obj->secs[sec->shdr->sh_link];
if (link_sec->shdr->sh_type != SHT_STRTAB) {
pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
return -EINVAL;
}
n = sec->shdr->sh_size / sec->shdr->sh_entsize;
sym = sec->data->d_buf;
for (i = 0; i < n; i++, sym++) {
int sym_type = ELF64_ST_TYPE(sym->st_info);
int sym_bind = ELF64_ST_BIND(sym->st_info);
int sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
if (i == 0) {
if (sym->st_name != 0 || sym->st_info != 0
|| sym->st_other != 0 || sym->st_shndx != 0
|| sym->st_value != 0 || sym->st_size != 0) {
pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
return -EINVAL;
}
continue;
}
if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
pr_warn("ELF sym #%d in section #%zu has unsupported symbol binding %d\n",
i, sec->sec_idx, sym_bind);
return -EINVAL;
}
if (sym_vis != STV_DEFAULT && sym_vis != STV_HIDDEN) {
pr_warn("ELF sym #%d in section #%zu has unsupported symbol visibility %d\n",
i, sec->sec_idx, sym_vis);
return -EINVAL;
}
if (sym->st_shndx == 0) {
if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
|| sym->st_value != 0 || sym->st_size != 0) {
pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
i, obj->filename);
return -EINVAL;
}
continue;
}
if (sym->st_shndx < SHN_LORESERVE && sym->st_shndx >= obj->sec_cnt) {
pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
return -EINVAL;
}
if (sym_type == STT_SECTION) {
if (sym->st_value != 0)
return -EINVAL;
continue;
}
}
return 0;
}
static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
{
struct src_sec *link_sec, *sym_sec;
Elf64_Rel *relo;
int i, n;
if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
return -EINVAL;
if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
return -EINVAL;
/* SHT_REL's sh_link should point to SYMTAB */
if (sec->shdr->sh_link != obj->symtab_sec_idx) {
pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
return -EINVAL;
}
/* SHT_REL's sh_info points to relocated section */
if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
return -EINVAL;
}
link_sec = &obj->secs[sec->shdr->sh_info];
/* .rel<secname> -> <secname> pattern is followed */
if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
|| strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
pr_warn("ELF relo section #%zu name has invalid name in %s\n",
sec->sec_idx, obj->filename);
return -EINVAL;
}
/* don't further validate relocations for ignored sections */
if (link_sec->skipped)
return 0;
/* relocatable section is data or instructions */
if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
return -EINVAL;
}
/* check sanity of each relocation */
n = sec->shdr->sh_size / sec->shdr->sh_entsize;
relo = sec->data->d_buf;
sym_sec = &obj->secs[obj->symtab_sec_idx];
for (i = 0; i < n; i++, relo++) {
size_t sym_idx = ELF64_R_SYM(relo->r_info);
size_t sym_type = ELF64_R_TYPE(relo->r_info);
if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32 &&
sym_type != R_BPF_64_ABS64 && sym_type != R_BPF_64_ABS32) {
pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
i, sec->sec_idx, sym_type, obj->filename);
return -EINVAL;
}
if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
i, sec->sec_idx, sym_idx, obj->filename);
return -EINVAL;
}
if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
i, sec->sec_idx, sym_idx, obj->filename);
return -EINVAL;
}
}
}
return 0;
}
static int check_btf_type_id(__u32 *type_id, void *ctx)
{
struct btf *btf = ctx;
if (*type_id >= btf__type_cnt(btf))
return -EINVAL;
return 0;
}
static int check_btf_str_off(__u32 *str_off, void *ctx)
{
struct btf *btf = ctx;
const char *s;
s = btf__str_by_offset(btf, *str_off);
if (!s)
return -EINVAL;
return 0;
}
static int linker_sanity_check_btf(struct src_obj *obj)
{
struct btf_type *t;
int i, n, err;
if (!obj->btf)
return 0;
n = btf__type_cnt(obj->btf);
for (i = 1; i < n; i++) {
struct btf_field_iter it;
__u32 *type_id, *str_off;
t = btf_type_by_id(obj->btf, i);
err = btf_field_iter_init(&it, t, BTF_FIELD_ITER_IDS);
if (err)
return err;
while ((type_id = btf_field_iter_next(&it))) {
if (*type_id >= n)
return -EINVAL;
}
err = btf_field_iter_init(&it, t, BTF_FIELD_ITER_STRS);
if (err)
return err;
while ((str_off = btf_field_iter_next(&it))) {
if (!btf__str_by_offset(obj->btf, *str_off))
return -EINVAL;
}
}
return 0;
}
static int linker_sanity_check_btf_ext(struct src_obj *obj)
{
int err = 0;
if (!obj->btf_ext)
return 0;
/* can't use .BTF.ext without .BTF */
if (!obj->btf)
return -EINVAL;
err = err ?: btf_ext_visit_type_ids(obj->btf_ext, check_btf_type_id, obj->btf);
err = err ?: btf_ext_visit_str_offs(obj->btf_ext, check_btf_str_off, obj->btf);
if (err)
return err;
return 0;
}
static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct src_sec *src_sec)
{
Elf_Scn *scn;
Elf_Data *data;
Elf64_Shdr *shdr;
int name_off;
dst_sec->sec_sz = 0;
dst_sec->sec_idx = 0;
dst_sec->ephemeral = src_sec->ephemeral;
/* ephemeral sections are just thin section shells lacking most parts */
if (src_sec->ephemeral)
return 0;
scn = elf_newscn(linker->elf);
if (!scn)
return -ENOMEM;
data = elf_newdata(scn);
if (!data)
return -ENOMEM;
shdr = elf64_getshdr(scn);
if (!shdr)
return -ENOMEM;
dst_sec->scn = scn;
dst_sec->shdr = shdr;
dst_sec->data = data;
dst_sec->sec_idx = elf_ndxscn(scn);
name_off = strset__add_str(linker->strtab_strs, src_sec->sec_name);
if (name_off < 0)
return name_off;
shdr->sh_name = name_off;
shdr->sh_type = src_sec->shdr->sh_type;
shdr->sh_flags = src_sec->shdr->sh_flags;
shdr->sh_size = 0;
/* sh_link and sh_info have different meaning for different types of
* sections, so we leave it up to the caller code to fill them in, if
* necessary
*/
shdr->sh_link = 0;
shdr->sh_info = 0;
shdr->sh_addralign = src_sec->shdr->sh_addralign;
shdr->sh_entsize = src_sec->shdr->sh_entsize;
data->d_type = src_sec->data->d_type;
data->d_size = 0;
data->d_buf = NULL;
data->d_align = src_sec->data->d_align;
data->d_off = 0;
return 0;
}
static struct dst_sec *find_dst_sec_by_name(struct bpf_linker *linker, const char *sec_name)
{
struct dst_sec *sec;
int i;
for (i = 1; i < linker->sec_cnt; i++) {
sec = &linker->secs[i];
if (strcmp(sec->sec_name, sec_name) == 0)
return sec;
}
return NULL;
}
static bool secs_match(struct dst_sec *dst, struct src_sec *src)
{
if (dst->ephemeral || src->ephemeral)
return true;
if (dst->shdr->sh_type != src->shdr->sh_type) {
pr_warn("sec %s types mismatch\n", dst->sec_name);
return false;
}
if (dst->shdr->sh_flags != src->shdr->sh_flags) {
pr_warn("sec %s flags mismatch\n", dst->sec_name);
return false;
}
if (dst->shdr->sh_entsize != src->shdr->sh_entsize) {
pr_warn("sec %s entsize mismatch\n", dst->sec_name);
return false;
}
return true;
}
static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec)
{
if (dst_sec->sec_sz != src_sec->shdr->sh_size)
return false;
if (memcmp(dst_sec->raw_data, src_sec->data->d_buf, dst_sec->sec_sz) != 0)
return false;
return true;
}
static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
{
void *tmp;
size_t dst_align, src_align;
size_t dst_align_sz, dst_final_sz;
int err;
/* Ephemeral source section doesn't contribute anything to ELF
* section data.
*/
if (src->ephemeral)
return 0;
/* Some sections (like .maps) can contain both externs (and thus be
* ephemeral) and non-externs (map definitions). So it's possible that
* it has to be "upgraded" from ephemeral to non-ephemeral when the
* first non-ephemeral entity appears. In such case, we add ELF
* section, data, etc.
*/
if (dst->ephemeral) {
err = init_sec(linker, dst, src);
if (err)
return err;
}
dst_align = dst->shdr->sh_addralign;
src_align = src->shdr->sh_addralign;
if (dst_align == 0)
dst_align = 1;
if (dst_align < src_align)
dst_align = src_align;
dst_align_sz = (dst->sec_sz + dst_align - 1) / dst_align * dst_align;
/* no need to re-align final size */
dst_final_sz = dst_align_sz + src->shdr->sh_size;
if (src->shdr->sh_type != SHT_NOBITS) {
tmp = realloc(dst->raw_data, dst_final_sz);
/* If dst_align_sz == 0, realloc() behaves in a special way:
* 1. When dst->raw_data is NULL it returns:
* "either NULL or a pointer suitable to be passed to free()" [1].
* 2. When dst->raw_data is not-NULL it frees dst->raw_data and returns NULL,
* thus invalidating any "pointer suitable to be passed to free()" obtained
* at step (1).
*
* The dst_align_sz > 0 check avoids error exit after (2), otherwise
* dst->raw_data would be freed again in bpf_linker__free().
*
* [1] man 3 realloc
*/
if (!tmp && dst_align_sz > 0)
return -ENOMEM;
dst->raw_data = tmp;
/* pad dst section, if it's alignment forced size increase */
memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
/* now copy src data at a properly aligned offset */
memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
}
dst->sec_sz = dst_final_sz;
dst->shdr->sh_size = dst_final_sz;
dst->data->d_size = dst_final_sz;
dst->shdr->sh_addralign = dst_align;
dst->data->d_align = dst_align;
src->dst_off = dst_align_sz;
return 0;
}
static bool is_data_sec(struct src_sec *sec)
{
if (!sec || sec->skipped)
return false;
/* ephemeral sections are data sections, e.g., .kconfig, .ksyms */
if (sec->ephemeral)
return true;
return sec->shdr->sh_type == SHT_PROGBITS || sec->shdr->sh_type == SHT_NOBITS;
}
static bool is_relo_sec(struct src_sec *sec)
{
if (!sec || sec->skipped || sec->ephemeral)
return false;
return sec->shdr->sh_type == SHT_REL;
}
static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj)
{
int i, err;
for (i = 1; i < obj->sec_cnt; i++) {
struct src_sec *src_sec;
struct dst_sec *dst_sec;
src_sec = &obj->secs[i];
if (!is_data_sec(src_sec))
continue;
dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
if (!dst_sec) {
dst_sec = add_dst_sec(linker, src_sec->sec_name);
if (!dst_sec)
return -ENOMEM;
err = init_sec(linker, dst_sec, src_sec);
if (err) {
pr_warn("failed to init section '%s'\n", src_sec->sec_name);
return err;
}
} else {
if (!secs_match(dst_sec, src_sec)) {
pr_warn("ELF sections %s are incompatible\n", src_sec->sec_name);
return -1;
}
/* "license" and "version" sections are deduped */
if (strcmp(src_sec->sec_name, "license") == 0
|| strcmp(src_sec->sec_name, "version") == 0) {
if (!sec_content_is_same(dst_sec, src_sec)) {
pr_warn("non-identical contents of section '%s' are not supported\n", src_sec->sec_name);
return -EINVAL;
}
src_sec->skipped = true;
src_sec->dst_id = dst_sec->id;
continue;
}
}
/* record mapped section index */
src_sec->dst_id = dst_sec->id;
err = extend_sec(linker, dst_sec, src_sec);
if (err)
return err;
}
return 0;
}
static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
{
struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
Elf64_Sym *sym = symtab->data->d_buf;
int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
int str_sec_idx = symtab->shdr->sh_link;
const char *sym_name;
obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
if (!obj->sym_map)
return -ENOMEM;
for (i = 0; i < n; i++, sym++) {
/* We already validated all-zero symbol #0 and we already
* appended it preventively to the final SYMTAB, so skip it.
*/
if (i == 0)
continue;
sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
if (!sym_name) {
pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
return -EINVAL;
}
err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
if (err)
return err;
}
return 0;
}
static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
{
struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
Elf64_Sym *syms = symtab->raw_data;
return &syms[sym_idx];
}
static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
{
struct glob_sym *glob_sym;
const char *name;
int i;
for (i = 0; i < linker->glob_sym_cnt; i++) {
glob_sym = &linker->glob_syms[i];
name = strset__data(linker->strtab_strs) + glob_sym->name_off;
if (strcmp(name, sym_name) == 0)
return glob_sym;
}
return NULL;
}
static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
{
struct glob_sym *syms, *sym;
syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
sizeof(*linker->glob_syms));
if (!syms)
return NULL;
sym = &syms[linker->glob_sym_cnt];
memset(sym, 0, sizeof(*sym));
sym->var_idx = -1;
linker->glob_syms = syms;
linker->glob_sym_cnt++;
return sym;
}
static bool glob_sym_btf_matches(const char *sym_name, bool exact,
const struct btf *btf1, __u32 id1,
const struct btf *btf2, __u32 id2)
{
const struct btf_type *t1, *t2;
bool is_static1, is_static2;
const char *n1, *n2;
int i, n;
recur:
n1 = n2 = NULL;
t1 = skip_mods_and_typedefs(btf1, id1, &id1);
t2 = skip_mods_and_typedefs(btf2, id2, &id2);
/* check if only one side is FWD, otherwise handle with common logic */
if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
n1 = btf__str_by_offset(btf1, t1->name_off);
n2 = btf__str_by_offset(btf2, t2->name_off);
if (strcmp(n1, n2) != 0) {
pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
sym_name, n1, n2);
return false;
}
/* validate if FWD kind matches concrete kind */
if (btf_is_fwd(t1)) {
if (btf_kflag(t1) && btf_is_union(t2))
return true;
if (!btf_kflag(t1) && btf_is_struct(t2))
return true;
pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
} else {
if (btf_kflag(t2) && btf_is_union(t1))
return true;
if (!btf_kflag(t2) && btf_is_struct(t1))
return true;
pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
}
return false;
}
if (btf_kind(t1) != btf_kind(t2)) {
pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
sym_name, btf_kind_str(t1), btf_kind_str(t2));
return false;
}
switch (btf_kind(t1)) {
case BTF_KIND_STRUCT:
case BTF_KIND_UNION:
case BTF_KIND_ENUM:
case BTF_KIND_ENUM64:
case BTF_KIND_FWD:
case BTF_KIND_FUNC:
case BTF_KIND_VAR:
n1 = btf__str_by_offset(btf1, t1->name_off);
n2 = btf__str_by_offset(btf2, t2->name_off);
if (strcmp(n1, n2) != 0) {
pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
sym_name, btf_kind_str(t1), n1, n2);
return false;
}
break;
default:
break;
}
switch (btf_kind(t1)) {
case BTF_KIND_UNKN: /* void */
case BTF_KIND_FWD:
return true;
case BTF_KIND_INT:
case BTF_KIND_FLOAT:
case BTF_KIND_ENUM:
case BTF_KIND_ENUM64:
/* ignore encoding for int and enum values for enum */
if (t1->size != t2->size) {
pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
return false;
}
return true;
case BTF_KIND_PTR:
/* just validate overall shape of the referenced type, so no
* contents comparison for struct/union, and allowed fwd vs
* struct/union
*/
exact = false;
id1 = t1->type;
id2 = t2->type;
goto recur;
case BTF_KIND_ARRAY:
/* ignore index type and array size */
id1 = btf_array(t1)->type;
id2 = btf_array(t2)->type;
goto recur;
case BTF_KIND_FUNC:
/* extern and global linkages are compatible */
is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
if (is_static1 != is_static2) {
pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
return false;
}
id1 = t1->type;
id2 = t2->type;
goto recur;
case BTF_KIND_VAR:
/* extern and global linkages are compatible */
is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
if (is_static1 != is_static2) {
pr_warn("global '%s': incompatible var '%s' linkage\n", sym_name, n1);
return false;
}
id1 = t1->type;
id2 = t2->type;
goto recur;
case BTF_KIND_STRUCT:
case BTF_KIND_UNION: {
const struct btf_member *m1, *m2;
if (!exact)
return true;
if (btf_vlen(t1) != btf_vlen(t2)) {
pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
return false;
}
n = btf_vlen(t1);
m1 = btf_members(t1);
m2 = btf_members(t2);
for (i = 0; i < n; i++, m1++, m2++) {
n1 = btf__str_by_offset(btf1, m1->name_off);
n2 = btf__str_by_offset(btf2, m2->name_off);
if (strcmp(n1, n2) != 0) {
pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
sym_name, i, n1, n2);
return false;
}
if (m1->offset != m2->offset) {
pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
sym_name, i, n1);
return false;
}
if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
return false;
}
return true;
}
case BTF_KIND_FUNC_PROTO: {
const struct btf_param *m1, *m2;
if (btf_vlen(t1) != btf_vlen(t2)) {
pr_warn("global '%s': incompatible number of %s params %u and %u\n",
sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
return false;
}
n = btf_vlen(t1);
m1 = btf_params(t1);
m2 = btf_params(t2);
for (i = 0; i < n; i++, m1++, m2++) {
/* ignore func arg names */
if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
return false;
}
/* now check return type as well */
id1 = t1->type;
id2 = t2->type;
goto recur;
}
/* skip_mods_and_typedefs() make this impossible */
case BTF_KIND_TYPEDEF:
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
/* DATASECs are never compared with each other */
case BTF_KIND_DATASEC:
default:
pr_warn("global '%s': unsupported BTF kind %s\n",
sym_name, btf_kind_str(t1));
return false;
}
}
static bool map_defs_match(const char *sym_name,
const struct btf *main_btf,
const struct btf_map_def *main_def,
const struct btf_map_def *main_inner_def,
const struct btf *extra_btf,
const struct btf_map_def *extra_def,
const struct btf_map_def *extra_inner_def)
{
const char *reason;
if (main_def->map_type != extra_def->map_type) {
reason = "type";
goto mismatch;
}
/* check key type/size match */
if (main_def->key_size != extra_def->key_size) {
reason = "key_size";
goto mismatch;
}
if (!!main_def->key_type_id != !!extra_def->key_type_id) {
reason = "key type";
goto mismatch;
}
if ((main_def->parts & MAP_DEF_KEY_TYPE)
&& !glob_sym_btf_matches(sym_name, true /*exact*/,
main_btf, main_def->key_type_id,
extra_btf, extra_def->key_type_id)) {
reason = "key type";
goto mismatch;
}
/* validate value type/size match */
if (main_def->value_size != extra_def->value_size) {
reason = "value_size";
goto mismatch;
}
if (!!main_def->value_type_id != !!extra_def->value_type_id) {
reason = "value type";
goto mismatch;
}
if ((main_def->parts & MAP_DEF_VALUE_TYPE)
&& !glob_sym_btf_matches(sym_name, true /*exact*/,
main_btf, main_def->value_type_id,
extra_btf, extra_def->value_type_id)) {
reason = "key type";
goto mismatch;
}
if (main_def->max_entries != extra_def->max_entries) {
reason = "max_entries";
goto mismatch;
}
if (main_def->map_flags != extra_def->map_flags) {
reason = "map_flags";
goto mismatch;
}
if (main_def->numa_node != extra_def->numa_node) {
reason = "numa_node";
goto mismatch;
}
if (main_def->pinning != extra_def->pinning) {
reason = "pinning";
goto mismatch;
}
if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
reason = "inner map";
goto mismatch;
}
if (main_def->parts & MAP_DEF_INNER_MAP) {
char inner_map_name[128];
snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
return map_defs_match(inner_map_name,
main_btf, main_inner_def, NULL,
extra_btf, extra_inner_def, NULL);
}
return true;
mismatch:
pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
return false;
}
static bool glob_map_defs_match(const char *sym_name,
struct bpf_linker *linker, struct glob_sym *glob_sym,
struct src_obj *obj, Elf64_Sym *sym, int btf_id)
{
struct btf_map_def dst_def = {}, dst_inner_def = {};
struct btf_map_def src_def = {}, src_inner_def = {};
const struct btf_type *t;
int err;
t = btf__type_by_id(obj->btf, btf_id);
if (!btf_is_var(t)) {
pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
return false;
}
t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
if (err) {
pr_warn("global '%s': invalid map definition\n", sym_name);
return false;
}
/* re-parse existing map definition */
t = btf__type_by_id(linker->btf, glob_sym->btf_id);
t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
if (err) {
/* this should not happen, because we already validated it */
pr_warn("global '%s': invalid dst map definition\n", sym_name);
return false;
}
/* Currently extern map definition has to be complete and match
* concrete map definition exactly. This restriction might be lifted
* in the future.
*/
return map_defs_match(sym_name, linker->btf, &dst_def, &dst_inner_def,
obj->btf, &src_def, &src_inner_def);
}
static bool glob_syms_match(const char *sym_name,
struct bpf_linker *linker, struct glob_sym *glob_sym,
struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
{
const struct btf_type *src_t;
/* if we are dealing with externs, BTF types describing both global
* and extern VARs/FUNCs should be completely present in all files
*/
if (!glob_sym->btf_id || !btf_id) {
pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
return false;
}
src_t = btf__type_by_id(obj->btf, btf_id);
if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
btf_kind_str(src_t), sym_name);
return false;
}
/* deal with .maps definitions specially */
if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
if (!glob_sym_btf_matches(sym_name, true /*exact*/,
linker->btf, glob_sym->btf_id, obj->btf, btf_id))
return false;
return true;
}
static bool btf_is_non_static(const struct btf_type *t)
{
return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
|| (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
}
static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
int *out_btf_sec_id, int *out_btf_id)
{
int i, j, n, m, btf_id = 0;
const struct btf_type *t;
const struct btf_var_secinfo *vi;
const char *name;
if (!obj->btf) {
pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
return -EINVAL;
}
n = btf__type_cnt(obj->btf);
for (i = 1; i < n; i++) {
t = btf__type_by_id(obj->btf, i);
/* some global and extern FUNCs and VARs might not be associated with any
* DATASEC, so try to detect them in the same pass
*/
if (btf_is_non_static(t)) {
name = btf__str_by_offset(obj->btf, t->name_off);
if (strcmp(name, sym_name) != 0)
continue;
/* remember and still try to find DATASEC */
btf_id = i;
continue;
}
if (!btf_is_datasec(t))
continue;
vi = btf_var_secinfos(t);
for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
t = btf__type_by_id(obj->btf, vi->type);
name = btf__str_by_offset(obj->btf, t->name_off);
if (strcmp(name, sym_name) != 0)
continue;
if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
continue;
if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
continue;
if (btf_id && btf_id != vi->type) {
pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
sym_name, btf_id, vi->type);
return -EINVAL;
}
*out_btf_sec_id = i;
*out_btf_id = vi->type;
return 0;
}
}
/* free-floating extern or global FUNC */
if (btf_id) {
*out_btf_sec_id = 0;
*out_btf_id = btf_id;
return 0;
}
pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
return -ENOENT;
}
static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
{
struct src_sec *sec;
int i;
for (i = 1; i < obj->sec_cnt; i++) {
sec = &obj->secs[i];
if (strcmp(sec->sec_name, sec_name) == 0)
return sec;
}
return NULL;
}
static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
struct btf *src_btf, int src_id)
{
struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
struct btf_param *src_p, *dst_p;
const char *s;
int i, n, off;
/* We already made sure that source and destination types (FUNC or
* VAR) match in terms of types and argument names.
*/
if (btf_is_var(dst_t)) {
btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
return 0;
}
dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
/* now onto FUNC_PROTO types */
src_t = btf_type_by_id(src_btf, src_t->type);
dst_t = btf_type_by_id(dst_btf, dst_t->type);
/* Fill in all the argument names, which for extern FUNCs are missing.
* We'll end up with two copies of FUNCs/VARs for externs, but that
* will be taken care of by BTF dedup at the very end.
* It might be that BTF types for extern in one file has less/more BTF
* information (e.g., FWD instead of full STRUCT/UNION information),
* but that should be (in most cases, subject to BTF dedup rules)
* handled and resolved by BTF dedup algorithm as well, so we won't
* worry about it. Our only job is to make sure that argument names
* are populated on both sides, otherwise BTF dedup will pedantically
* consider them different.
*/
src_p = btf_params(src_t);
dst_p = btf_params(dst_t);
for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
if (!src_p->name_off)
continue;
/* src_btf has more complete info, so add name to dst_btf */
s = btf__str_by_offset(src_btf, src_p->name_off);
off = btf__add_str(dst_btf, s);
if (off < 0)
return off;
dst_p->name_off = off;
}
return 0;
}
static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
{
sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
}
static void sym_update_type(Elf64_Sym *sym, int sym_type)
{
sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
}
static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
{
/* libelf doesn't provide setters for ST_VISIBILITY,
* but it is stored in the lower 2 bits of st_other
*/
sym->st_other &= ~0x03;
sym->st_other |= sym_vis;
}
static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
{
struct src_sec *src_sec = NULL;
struct dst_sec *dst_sec = NULL;
struct glob_sym *glob_sym = NULL;
int name_off, sym_type, sym_bind, sym_vis, err;
int btf_sec_id = 0, btf_id = 0;
size_t dst_sym_idx;
Elf64_Sym *dst_sym;
bool sym_is_extern;
sym_type = ELF64_ST_TYPE(sym->st_info);
sym_bind = ELF64_ST_BIND(sym->st_info);
sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
sym_is_extern = sym->st_shndx == SHN_UNDEF;
if (sym_is_extern) {
if (!obj->btf) {
pr_warn("externs without BTF info are not supported\n");
return -ENOTSUP;
}
} else if (sym->st_shndx < SHN_LORESERVE) {
src_sec = &obj->secs[sym->st_shndx];
if (src_sec->skipped)
return 0;
dst_sec = &linker->secs[src_sec->dst_id];
/* allow only one STT_SECTION symbol per section */
if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
return 0;
}
}
if (sym_bind == STB_LOCAL)
goto add_sym;
/* find matching BTF info */
err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
if (err)
return err;
if (sym_is_extern && btf_sec_id) {
const char *sec_name = NULL;
const struct btf_type *t;
t = btf__type_by_id(obj->btf, btf_sec_id);
sec_name = btf__str_by_offset(obj->btf, t->name_off);
/* Clang puts unannotated extern vars into
* '.extern' BTF DATASEC. Treat them the same
* as unannotated extern funcs (which are
* currently not put into any DATASECs).
* Those don't have associated src_sec/dst_sec.
*/
if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
src_sec = find_src_sec_by_name(obj, sec_name);
if (!src_sec) {
pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
return -ENOENT;
}
dst_sec = &linker->secs[src_sec->dst_id];
}
}
glob_sym = find_glob_sym(linker, sym_name);
if (glob_sym) {
/* Preventively resolve to existing symbol. This is
* needed for further relocation symbol remapping in
* the next step of linking.
*/
obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
/* If both symbols are non-externs, at least one of
* them has to be STB_WEAK, otherwise they are in
* a conflict with each other.
*/
if (!sym_is_extern && !glob_sym->is_extern
&& !glob_sym->is_weak && sym_bind != STB_WEAK) {
pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
src_sym_idx, sym_name, obj->filename);
return -EINVAL;
}
if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
return -EINVAL;
dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
/* If new symbol is strong, then force dst_sym to be strong as
* well; this way a mix of weak and non-weak extern
* definitions will end up being strong.
*/
if (sym_bind == STB_GLOBAL) {
/* We still need to preserve type (NOTYPE or
* OBJECT/FUNC, depending on whether the symbol is
* extern or not)
*/
sym_update_bind(dst_sym, STB_GLOBAL);
glob_sym->is_weak = false;
}
/* Non-default visibility is "contaminating", with stricter
* visibility overwriting more permissive ones, even if more
* permissive visibility comes from just an extern definition.
* Currently only STV_DEFAULT and STV_HIDDEN are allowed and
* ensured by ELF symbol sanity checks above.
*/
if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
sym_update_visibility(dst_sym, sym_vis);
/* If the new symbol is extern, then regardless if
* existing symbol is extern or resolved global, just
* keep the existing one untouched.
*/
if (sym_is_extern)
return 0;
/* If existing symbol is a strong resolved symbol, bail out,
* because we lost resolution battle have nothing to
* contribute. We already checked above that there is no
* strong-strong conflict. We also already tightened binding
* and visibility, so nothing else to contribute at that point.
*/
if (!glob_sym->is_extern && sym_bind == STB_WEAK)
return 0;
/* At this point, new symbol is strong non-extern,
* so overwrite glob_sym with new symbol information.
* Preserve binding and visibility.
*/
sym_update_type(dst_sym, sym_type);
dst_sym->st_shndx = dst_sec->sec_idx;
dst_sym->st_value = src_sec->dst_off + sym->st_value;
dst_sym->st_size = sym->st_size;
/* see comment below about dst_sec->id vs dst_sec->sec_idx */
glob_sym->sec_id = dst_sec->id;
glob_sym->is_extern = false;
if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
obj->btf, btf_id))
return -EINVAL;
/* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
glob_sym->underlying_btf_id = 0;
obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
return 0;
}
add_sym:
name_off = strset__add_str(linker->strtab_strs, sym_name);
if (name_off < 0)
return name_off;
dst_sym = add_new_sym(linker, &dst_sym_idx);
if (!dst_sym)
return -ENOMEM;
dst_sym->st_name = name_off;
dst_sym->st_info = sym->st_info;
dst_sym->st_other = sym->st_other;
dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
dst_sym->st_size = sym->st_size;
obj->sym_map[src_sym_idx] = dst_sym_idx;
if (sym_type == STT_SECTION && dst_sym) {
dst_sec->sec_sym_idx = dst_sym_idx;
dst_sym->st_value = 0;
}
if (sym_bind != STB_LOCAL) {
glob_sym = add_glob_sym(linker);
if (!glob_sym)
return -ENOMEM;
glob_sym->sym_idx = dst_sym_idx;
/* we use dst_sec->id (and not dst_sec->sec_idx), because
* ephemeral sections (.kconfig, .ksyms, etc) don't have
* sec_idx (as they don't have corresponding ELF section), but
* still have id. .extern doesn't have even ephemeral section
* associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
*/
glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
glob_sym->name_off = name_off;
/* we will fill btf_id in during BTF merging step */
glob_sym->btf_id = 0;
glob_sym->is_extern = sym_is_extern;
glob_sym->is_weak = sym_bind == STB_WEAK;
}
return 0;
}
static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
{
struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
int i, err;
for (i = 1; i < obj->sec_cnt; i++) {
struct src_sec *src_sec, *src_linked_sec;
struct dst_sec *dst_sec, *dst_linked_sec;
Elf64_Rel *src_rel, *dst_rel;
int j, n;
src_sec = &obj->secs[i];
if (!is_relo_sec(src_sec))
continue;
/* shdr->sh_info points to relocatable section */
src_linked_sec = &obj->secs[src_sec->shdr->sh_info];
if (src_linked_sec->skipped)
continue;
dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
if (!dst_sec) {
dst_sec = add_dst_sec(linker, src_sec->sec_name);
if (!dst_sec)
return -ENOMEM;
err = init_sec(linker, dst_sec, src_sec);
if (err) {
pr_warn("failed to init section '%s'\n", src_sec->sec_name);
return err;
}
} else if (!secs_match(dst_sec, src_sec)) {
pr_warn("sections %s are not compatible\n", src_sec->sec_name);
return -1;
}
/* shdr->sh_link points to SYMTAB */
dst_sec->shdr->sh_link = linker->symtab_sec_idx;
/* shdr->sh_info points to relocated section */
dst_linked_sec = &linker->secs[src_linked_sec->dst_id];
dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
src_sec->dst_id = dst_sec->id;
err = extend_sec(linker, dst_sec, src_sec);
if (err)
return err;
src_rel = src_sec->data->d_buf;
dst_rel = dst_sec->raw_data + src_sec->dst_off;
n = src_sec->shdr->sh_size / src_sec->shdr->sh_entsize;
for (j = 0; j < n; j++, src_rel++, dst_rel++) {
size_t src_sym_idx, dst_sym_idx, sym_type;
Elf64_Sym *src_sym;
src_sym_idx = ELF64_R_SYM(src_rel->r_info);
src_sym = src_symtab->data->d_buf + sizeof(*src_sym) * src_sym_idx;
dst_sym_idx = obj->sym_map[src_sym_idx];
dst_rel->r_offset += src_linked_sec->dst_off;
sym_type = ELF64_R_TYPE(src_rel->r_info);
dst_rel->r_info = ELF64_R_INFO(dst_sym_idx, sym_type);
if (ELF64_ST_TYPE(src_sym->st_info) == STT_SECTION) {
struct src_sec *sec = &obj->secs[src_sym->st_shndx];
struct bpf_insn *insn;
if (src_linked_sec->shdr->sh_flags & SHF_EXECINSTR) {
/* calls to the very first static function inside
* .text section at offset 0 will
* reference section symbol, not the
* function symbol. Fix that up,
* otherwise it won't be possible to
* relocate calls to two different
* static functions with the same name
* (rom two different object files)
*/
insn = dst_linked_sec->raw_data + dst_rel->r_offset;
if (insn->code == (BPF_JMP | BPF_CALL))
insn->imm += sec->dst_off / sizeof(struct bpf_insn);
else
insn->imm += sec->dst_off;
} else {
pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
return -EINVAL;
}
}
}
}
return 0;
}
static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
int sym_type, const char *sym_name)
{
struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
Elf64_Sym *sym = symtab->data->d_buf;
int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
int str_sec_idx = symtab->shdr->sh_link;
const char *name;
for (i = 0; i < n; i++, sym++) {
if (sym->st_shndx != sec_idx)
continue;
if (ELF64_ST_TYPE(sym->st_info) != sym_type)
continue;
name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
if (!name)
return NULL;
if (strcmp(sym_name, name) != 0)
continue;
return sym;
}
return NULL;
}
static int linker_fixup_btf(struct src_obj *obj)
{
const char *sec_name;
struct src_sec *sec;
int i, j, n, m;
if (!obj->btf)
return 0;
n = btf__type_cnt(obj->btf);
for (i = 1; i < n; i++) {
struct btf_var_secinfo *vi;
struct btf_type *t;
t = btf_type_by_id(obj->btf, i);
if (btf_kind(t) != BTF_KIND_DATASEC)
continue;
sec_name = btf__str_by_offset(obj->btf, t->name_off);
sec = find_src_sec_by_name(obj, sec_name);
if (sec) {
/* record actual section size, unless ephemeral */
if (sec->shdr)
t->size = sec->shdr->sh_size;
} else {
/* BTF can have some sections that are not represented
* in ELF, e.g., .kconfig, .ksyms, .extern, which are used
* for special extern variables.
*
* For all but one such special (ephemeral)
* sections, we pre-create "section shells" to be able
* to keep track of extra per-section metadata later
* (e.g., those BTF extern variables).
*
* .extern is even more special, though, because it
* contains extern variables that need to be resolved
* by static linker, not libbpf and kernel. When such
* externs are resolved, we are going to remove them
* from .extern BTF section and might end up not
* needing it at all. Each resolved extern should have
* matching non-extern VAR/FUNC in other sections.
*
* We do support leaving some of the externs
* unresolved, though, to support cases of building
* libraries, which will later be linked against final
* BPF applications. So if at finalization we still
* see unresolved externs, we'll create .extern
* section on our own.
*/
if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
continue;
sec = add_src_sec(obj, sec_name);
if (!sec)
return -ENOMEM;
sec->ephemeral = true;
sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
}
/* remember ELF section and its BTF type ID match */
sec->sec_type_id = i;
/* fix up variable offsets */
vi = btf_var_secinfos(t);
for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
const char *var_name;
int var_linkage;
Elf64_Sym *sym;
/* could be a variable or function */
if (!btf_is_var(vt))
continue;
var_name = btf__str_by_offset(obj->btf, vt->name_off);
var_linkage = btf_var(vt)->linkage;
/* no need to patch up static or extern vars */
if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
continue;
sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT, var_name);
if (!sym) {
pr_warn("failed to find symbol for variable '%s' in section '%s'\n", var_name, sec_name);
return -ENOENT;
}
vi->offset = sym->st_value;
}
}
return 0;
}
static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
{
const struct btf_type *t;
int i, j, n, start_id, id, err;
const char *name;
if (!obj->btf)
return 0;
start_id = btf__type_cnt(linker->btf);
n = btf__type_cnt(obj->btf);
obj->btf_type_map = calloc(n + 1, sizeof(int));
if (!obj->btf_type_map)
return -ENOMEM;
for (i = 1; i < n; i++) {
struct glob_sym *glob_sym = NULL;
t = btf__type_by_id(obj->btf, i);
/* DATASECs are handled specially below */
if (btf_kind(t) == BTF_KIND_DATASEC)
continue;
if (btf_is_non_static(t)) {
/* there should be glob_sym already */
name = btf__str_by_offset(obj->btf, t->name_off);
glob_sym = find_glob_sym(linker, name);
/* VARs without corresponding glob_sym are those that
* belong to skipped/deduplicated sections (i.e.,
* license and version), so just skip them
*/
if (!glob_sym)
continue;
/* linker_append_elf_sym() might have requested
* updating underlying type ID, if extern was resolved
* to strong symbol or weak got upgraded to non-weak
*/
if (glob_sym->underlying_btf_id == 0)
glob_sym->underlying_btf_id = -t->type;
/* globals from previous object files that match our
* VAR/FUNC already have a corresponding associated
* BTF type, so just make sure to use it
*/
if (glob_sym->btf_id) {
/* reuse existing BTF type for global var/func */
obj->btf_type_map[i] = glob_sym->btf_id;
continue;
}
}
id = btf__add_type(linker->btf, obj->btf, t);
if (id < 0) {
pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
return id;
}
obj->btf_type_map[i] = id;
/* record just appended BTF type for var/func */
if (glob_sym) {
glob_sym->btf_id = id;
glob_sym->underlying_btf_id = -t->type;
}
}
/* remap all the types except DATASECs */
n = btf__type_cnt(linker->btf);
for (i = start_id; i < n; i++) {
struct btf_type *dst_t = btf_type_by_id(linker->btf, i);
struct btf_field_iter it;
__u32 *type_id;
err = btf_field_iter_init(&it, dst_t, BTF_FIELD_ITER_IDS);
if (err)
return err;
while ((type_id = btf_field_iter_next(&it))) {
int new_id = obj->btf_type_map[*type_id];
/* Error out if the type wasn't remapped. Ignore VOID which stays VOID. */
if (new_id == 0 && *type_id != 0) {
pr_warn("failed to find new ID mapping for original BTF type ID %u\n",
*type_id);
return -EINVAL;
}
*type_id = obj->btf_type_map[*type_id];
}
}
/* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
* actual type), if necessary
*/
for (i = 0; i < linker->glob_sym_cnt; i++) {
struct glob_sym *glob_sym = &linker->glob_syms[i];
struct btf_type *glob_t;
if (glob_sym->underlying_btf_id >= 0)
continue;
glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
glob_t->type = glob_sym->underlying_btf_id;
}
/* append DATASEC info */
for (i = 1; i < obj->sec_cnt; i++) {
struct src_sec *src_sec;
struct dst_sec *dst_sec;
const struct btf_var_secinfo *src_var;
struct btf_var_secinfo *dst_var;
src_sec = &obj->secs[i];
if (!src_sec->sec_type_id || src_sec->skipped)
continue;
dst_sec = &linker->secs[src_sec->dst_id];
/* Mark section as having BTF regardless of the presence of
* variables. In some cases compiler might generate empty BTF
* with no variables information. E.g., when promoting local
* array/structure variable initial values and BPF object
* file otherwise has no read-only static variables in
* .rodata. We need to preserve such empty BTF and just set
* correct section size.
*/
dst_sec->has_btf = true;
t = btf__type_by_id(obj->btf, src_sec->sec_type_id);
src_var = btf_var_secinfos(t);
n = btf_vlen(t);
for (j = 0; j < n; j++, src_var++) {
void *sec_vars = dst_sec->sec_vars;
int new_id = obj->btf_type_map[src_var->type];
struct glob_sym *glob_sym = NULL;
t = btf_type_by_id(linker->btf, new_id);
if (btf_is_non_static(t)) {
name = btf__str_by_offset(linker->btf, t->name_off);
glob_sym = find_glob_sym(linker, name);
if (glob_sym->sec_id != dst_sec->id) {
pr_warn("global '%s': section mismatch %d vs %d\n",
name, glob_sym->sec_id, dst_sec->id);
return -EINVAL;
}
}
/* If there is already a member (VAR or FUNC) mapped
* to the same type, don't add a duplicate entry.
* This will happen when multiple object files define
* the same extern VARs/FUNCs.
*/
if (glob_sym && glob_sym->var_idx >= 0) {
__s64 sz;
dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
/* Because underlying BTF type might have
* changed, so might its size have changed, so
* re-calculate and update it in sec_var.
*/
sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
if (sz < 0) {
pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
name, (int)sz);
return -EINVAL;
}
dst_var->size = sz;
continue;
}
sec_vars = libbpf_reallocarray(sec_vars,
dst_sec->sec_var_cnt + 1,
sizeof(*dst_sec->sec_vars));
if (!sec_vars)
return -ENOMEM;
dst_sec->sec_vars = sec_vars;
dst_sec->sec_var_cnt++;
dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
dst_var->type = obj->btf_type_map[src_var->type];
dst_var->size = src_var->size;
dst_var->offset = src_sec->dst_off + src_var->offset;
if (glob_sym)
glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
}
}
return 0;
}
static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
{
void *tmp;
tmp = libbpf_reallocarray(ext_data->recs, ext_data->rec_cnt + 1, ext_data->rec_sz);
if (!tmp)
return NULL;
ext_data->recs = tmp;
tmp += ext_data->rec_cnt * ext_data->rec_sz;
memcpy(tmp, src_rec, ext_data->rec_sz);
ext_data->rec_cnt++;
return tmp;
}
static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
{
const struct btf_ext_info_sec *ext_sec;
const char *sec_name, *s;
struct src_sec *src_sec;
struct dst_sec *dst_sec;
int rec_sz, str_off, i;
if (!obj->btf_ext)
return 0;
rec_sz = obj->btf_ext->func_info.rec_size;
for_each_btf_ext_sec(&obj->btf_ext->func_info, ext_sec) {
struct bpf_func_info_min *src_rec, *dst_rec;
sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
src_sec = find_src_sec_by_name(obj, sec_name);
if (!src_sec) {
pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
return -EINVAL;
}
dst_sec = &linker->secs[src_sec->dst_id];
if (dst_sec->func_info.rec_sz == 0)
dst_sec->func_info.rec_sz = rec_sz;
if (dst_sec->func_info.rec_sz != rec_sz) {
pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
return -EINVAL;
}
for_each_btf_ext_rec(&obj->btf_ext->func_info, ext_sec, i, src_rec) {
dst_rec = add_btf_ext_rec(&dst_sec->func_info, src_rec);
if (!dst_rec)
return -ENOMEM;
dst_rec->insn_off += src_sec->dst_off;
dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
}
}
rec_sz = obj->btf_ext->line_info.rec_size;
for_each_btf_ext_sec(&obj->btf_ext->line_info, ext_sec) {
struct bpf_line_info_min *src_rec, *dst_rec;
sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
src_sec = find_src_sec_by_name(obj, sec_name);
if (!src_sec) {
pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
return -EINVAL;
}
dst_sec = &linker->secs[src_sec->dst_id];
if (dst_sec->line_info.rec_sz == 0)
dst_sec->line_info.rec_sz = rec_sz;
if (dst_sec->line_info.rec_sz != rec_sz) {
pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
return -EINVAL;
}
for_each_btf_ext_rec(&obj->btf_ext->line_info, ext_sec, i, src_rec) {
dst_rec = add_btf_ext_rec(&dst_sec->line_info, src_rec);
if (!dst_rec)
return -ENOMEM;
dst_rec->insn_off += src_sec->dst_off;
s = btf__str_by_offset(obj->btf, src_rec->file_name_off);
str_off = btf__add_str(linker->btf, s);
if (str_off < 0)
return -ENOMEM;
dst_rec->file_name_off = str_off;
s = btf__str_by_offset(obj->btf, src_rec->line_off);
str_off = btf__add_str(linker->btf, s);
if (str_off < 0)
return -ENOMEM;
dst_rec->line_off = str_off;
/* dst_rec->line_col is fine */
}
}
rec_sz = obj->btf_ext->core_relo_info.rec_size;
for_each_btf_ext_sec(&obj->btf_ext->core_relo_info, ext_sec) {
struct bpf_core_relo *src_rec, *dst_rec;
sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
src_sec = find_src_sec_by_name(obj, sec_name);
if (!src_sec) {
pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
return -EINVAL;
}
dst_sec = &linker->secs[src_sec->dst_id];
if (dst_sec->core_relo_info.rec_sz == 0)
dst_sec->core_relo_info.rec_sz = rec_sz;
if (dst_sec->core_relo_info.rec_sz != rec_sz) {
pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
return -EINVAL;
}
for_each_btf_ext_rec(&obj->btf_ext->core_relo_info, ext_sec, i, src_rec) {
dst_rec = add_btf_ext_rec(&dst_sec->core_relo_info, src_rec);
if (!dst_rec)
return -ENOMEM;
dst_rec->insn_off += src_sec->dst_off;
dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
s = btf__str_by_offset(obj->btf, src_rec->access_str_off);
str_off = btf__add_str(linker->btf, s);
if (str_off < 0)
return -ENOMEM;
dst_rec->access_str_off = str_off;
/* dst_rec->kind is fine */
}
}
return 0;
}
int bpf_linker__finalize(struct bpf_linker *linker)
{
struct dst_sec *sec;
size_t strs_sz;
const void *strs;
int err, i;
if (!linker->elf)
return libbpf_err(-EINVAL);
err = finalize_btf(linker);
if (err)
return libbpf_err(err);
/* Finalize strings */
strs_sz = strset__data_size(linker->strtab_strs);
strs = strset__data(linker->strtab_strs);
sec = &linker->secs[linker->strtab_sec_idx];
sec->data->d_align = 1;
sec->data->d_off = 0LL;
sec->data->d_buf = (void *)strs;
sec->data->d_type = ELF_T_BYTE;
sec->data->d_size = strs_sz;
sec->shdr->sh_size = strs_sz;
for (i = 1; i < linker->sec_cnt; i++) {
sec = &linker->secs[i];
/* STRTAB is handled specially above */
if (sec->sec_idx == linker->strtab_sec_idx)
continue;
/* special ephemeral sections (.ksyms, .kconfig, etc) */
if (!sec->scn)
continue;
sec->data->d_buf = sec->raw_data;
}
/* Finalize ELF layout */
if (elf_update(linker->elf, ELF_C_NULL) < 0) {
err = -errno;
pr_warn_elf("failed to finalize ELF layout");
return libbpf_err(err);
}
/* Write out final ELF contents */
if (elf_update(linker->elf, ELF_C_WRITE) < 0) {
err = -errno;
pr_warn_elf("failed to write ELF contents");
return libbpf_err(err);
}
elf_end(linker->elf);
close(linker->fd);
linker->elf = NULL;
linker->fd = -1;
return 0;
}
static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
size_t align, const void *raw_data, size_t raw_sz)
{
Elf_Scn *scn;
Elf_Data *data;
Elf64_Shdr *shdr;
int name_off;
name_off = strset__add_str(linker->strtab_strs, sec_name);
if (name_off < 0)
return name_off;
scn = elf_newscn(linker->elf);
if (!scn)
return -ENOMEM;
data = elf_newdata(scn);
if (!data)
return -ENOMEM;
shdr = elf64_getshdr(scn);
if (!shdr)
return -EINVAL;
shdr->sh_name = name_off;
shdr->sh_type = SHT_PROGBITS;
shdr->sh_flags = 0;
shdr->sh_size = raw_sz;
shdr->sh_link = 0;
shdr->sh_info = 0;
shdr->sh_addralign = align;
shdr->sh_entsize = 0;
data->d_type = ELF_T_BYTE;
data->d_size = raw_sz;
data->d_buf = (void *)raw_data;
data->d_align = align;
data->d_off = 0;
return 0;
}
static int finalize_btf(struct bpf_linker *linker)
{
LIBBPF_OPTS(btf_dedup_opts, opts);
struct btf *btf = linker->btf;
const void *raw_data;
int i, j, id, err;
__u32 raw_sz;
/* bail out if no BTF data was produced */
if (btf__type_cnt(linker->btf) == 1)
return 0;
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
if (!sec->has_btf)
continue;
id = btf__add_datasec(btf, sec->sec_name, sec->sec_sz);
if (id < 0) {
pr_warn("failed to add consolidated BTF type for datasec '%s': %d\n",
sec->sec_name, id);
return id;
}
for (j = 0; j < sec->sec_var_cnt; j++) {
struct btf_var_secinfo *vi = &sec->sec_vars[j];
if (btf__add_datasec_var_info(btf, vi->type, vi->offset, vi->size))
return -EINVAL;
}
}
err = finalize_btf_ext(linker);
if (err) {
pr_warn(".BTF.ext generation failed: %d\n", err);
return err;
}
opts.btf_ext = linker->btf_ext;
err = btf__dedup(linker->btf, &opts);
if (err) {
pr_warn("BTF dedup failed: %d\n", err);
return err;
}
/* Emit .BTF section */
raw_data = btf__raw_data(linker->btf, &raw_sz);
if (!raw_data)
return -ENOMEM;
err = emit_elf_data_sec(linker, BTF_ELF_SEC, 8, raw_data, raw_sz);
if (err) {
pr_warn("failed to write out .BTF ELF section: %d\n", err);
return err;
}
/* Emit .BTF.ext section */
if (linker->btf_ext) {
raw_data = btf_ext__raw_data(linker->btf_ext, &raw_sz);
if (!raw_data)
return -ENOMEM;
err = emit_elf_data_sec(linker, BTF_EXT_ELF_SEC, 8, raw_data, raw_sz);
if (err) {
pr_warn("failed to write out .BTF.ext ELF section: %d\n", err);
return err;
}
}
return 0;
}
static int emit_btf_ext_data(struct bpf_linker *linker, void *output,
const char *sec_name, struct btf_ext_sec_data *sec_data)
{
struct btf_ext_info_sec *sec_info;
void *cur = output;
int str_off;
size_t sz;
if (!sec_data->rec_cnt)
return 0;
str_off = btf__add_str(linker->btf, sec_name);
if (str_off < 0)
return -ENOMEM;
sec_info = cur;
sec_info->sec_name_off = str_off;
sec_info->num_info = sec_data->rec_cnt;
cur += sizeof(struct btf_ext_info_sec);
sz = sec_data->rec_cnt * sec_data->rec_sz;
memcpy(cur, sec_data->recs, sz);
cur += sz;
return cur - output;
}
static int finalize_btf_ext(struct bpf_linker *linker)
{
size_t funcs_sz = 0, lines_sz = 0, core_relos_sz = 0, total_sz = 0;
size_t func_rec_sz = 0, line_rec_sz = 0, core_relo_rec_sz = 0;
struct btf_ext_header *hdr;
void *data, *cur;
int i, err, sz;
/* validate that all sections have the same .BTF.ext record sizes
* and calculate total data size for each type of data (func info,
* line info, core relos)
*/
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
if (sec->func_info.rec_cnt) {
if (func_rec_sz == 0)
func_rec_sz = sec->func_info.rec_sz;
if (func_rec_sz != sec->func_info.rec_sz) {
pr_warn("mismatch in func_info record size %zu != %u\n",
func_rec_sz, sec->func_info.rec_sz);
return -EINVAL;
}
funcs_sz += sizeof(struct btf_ext_info_sec) + func_rec_sz * sec->func_info.rec_cnt;
}
if (sec->line_info.rec_cnt) {
if (line_rec_sz == 0)
line_rec_sz = sec->line_info.rec_sz;
if (line_rec_sz != sec->line_info.rec_sz) {
pr_warn("mismatch in line_info record size %zu != %u\n",
line_rec_sz, sec->line_info.rec_sz);
return -EINVAL;
}
lines_sz += sizeof(struct btf_ext_info_sec) + line_rec_sz * sec->line_info.rec_cnt;
}
if (sec->core_relo_info.rec_cnt) {
if (core_relo_rec_sz == 0)
core_relo_rec_sz = sec->core_relo_info.rec_sz;
if (core_relo_rec_sz != sec->core_relo_info.rec_sz) {
pr_warn("mismatch in core_relo_info record size %zu != %u\n",
core_relo_rec_sz, sec->core_relo_info.rec_sz);
return -EINVAL;
}
core_relos_sz += sizeof(struct btf_ext_info_sec) + core_relo_rec_sz * sec->core_relo_info.rec_cnt;
}
}
if (!funcs_sz && !lines_sz && !core_relos_sz)
return 0;
total_sz += sizeof(struct btf_ext_header);
if (funcs_sz) {
funcs_sz += sizeof(__u32); /* record size prefix */
total_sz += funcs_sz;
}
if (lines_sz) {
lines_sz += sizeof(__u32); /* record size prefix */
total_sz += lines_sz;
}
if (core_relos_sz) {
core_relos_sz += sizeof(__u32); /* record size prefix */
total_sz += core_relos_sz;
}
cur = data = calloc(1, total_sz);
if (!data)
return -ENOMEM;
hdr = cur;
hdr->magic = BTF_MAGIC;
hdr->version = BTF_VERSION;
hdr->flags = 0;
hdr->hdr_len = sizeof(struct btf_ext_header);
cur += sizeof(struct btf_ext_header);
/* All offsets are in bytes relative to the end of this header */
hdr->func_info_off = 0;
hdr->func_info_len = funcs_sz;
hdr->line_info_off = funcs_sz;
hdr->line_info_len = lines_sz;
hdr->core_relo_off = funcs_sz + lines_sz;
hdr->core_relo_len = core_relos_sz;
if (funcs_sz) {
*(__u32 *)cur = func_rec_sz;
cur += sizeof(__u32);
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->func_info);
if (sz < 0) {
err = sz;
goto out;
}
cur += sz;
}
}
if (lines_sz) {
*(__u32 *)cur = line_rec_sz;
cur += sizeof(__u32);
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->line_info);
if (sz < 0) {
err = sz;
goto out;
}
cur += sz;
}
}
if (core_relos_sz) {
*(__u32 *)cur = core_relo_rec_sz;
cur += sizeof(__u32);
for (i = 1; i < linker->sec_cnt; i++) {
struct dst_sec *sec = &linker->secs[i];
sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->core_relo_info);
if (sz < 0) {
err = sz;
goto out;
}
cur += sz;
}
}
linker->btf_ext = btf_ext__new(data, total_sz);
err = libbpf_get_error(linker->btf_ext);
if (err) {
linker->btf_ext = NULL;
pr_warn("failed to parse final .BTF.ext data: %d\n", err);
goto out;
}
out:
free(data);
return err;
}
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