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libbpf: add support for bpf_call
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- recognize relocation emitted by llvm
- since all regular function will be kept in .text section and llvm
  takes care of pc-relative offsets in bpf_call instruction
  simply copy all of .text to relevant program section while adjusting
  bpf_call instructions in program section to point to newly copied
  body of instructions from .text
- do so for all programs in the elf file
- set all programs types to the one passed to bpf_prog_load()

Note for elf files with multiple programs that use different
functions in .text section we need to do 'linker' style logic.
This work is still TBD

Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
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@4ast @borkmann
4ast authored and borkmann committed Dec 17, 2017
1 parent d98588c commit 48cca7e
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Showing 3 changed files with 134 additions and 44 deletions.
6 changes: 6 additions & 0 deletions tools/include/uapi/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -197,8 +197,14 @@ enum bpf_attach_type {
*/
#define BPF_F_STRICT_ALIGNMENT (1U << 0)

/* when bpf_ldimm64->src_reg == BPF_PSEUDO_MAP_FD, bpf_ldimm64->imm == fd */
#define BPF_PSEUDO_MAP_FD 1

/* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
* offset to another bpf function
*/
#define BPF_PSEUDO_CALL 1

/* flags for BPF_MAP_UPDATE_ELEM command */
#define BPF_ANY 0 /* create new element or update existing */
#define BPF_NOEXIST 1 /* create new element if it didn't exist */
Expand Down
2 changes: 1 addition & 1 deletion tools/lib/bpf/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ int bpf_create_map_in_map(enum bpf_map_type map_type, const char *name,
__u32 map_flags);

/* Recommend log buffer size */
#define BPF_LOG_BUF_SIZE 65536
#define BPF_LOG_BUF_SIZE (256 * 1024)
int bpf_load_program_name(enum bpf_prog_type type, const char *name,
const struct bpf_insn *insns,
size_t insns_cnt, const char *license,
Expand Down
170 changes: 127 additions & 43 deletions tools/lib/bpf/libbpf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -174,12 +174,19 @@ struct bpf_program {
char *name;
char *section_name;
struct bpf_insn *insns;
size_t insns_cnt;
size_t insns_cnt, main_prog_cnt;
enum bpf_prog_type type;

struct {
struct reloc_desc {
enum {
RELO_LD64,
RELO_CALL,
} type;
int insn_idx;
int map_idx;
union {
int map_idx;
int text_off;
};
} *reloc_desc;
int nr_reloc;

Expand Down Expand Up @@ -234,6 +241,7 @@ struct bpf_object {
} *reloc;
int nr_reloc;
int maps_shndx;
int text_shndx;
} efile;
/*
* All loaded bpf_object is linked in a list, which is
Expand Down Expand Up @@ -375,9 +383,13 @@ bpf_object__init_prog_names(struct bpf_object *obj)
size_t pi, si;

for (pi = 0; pi < obj->nr_programs; pi++) {
char *name = NULL;
const char *name = NULL;

prog = &obj->programs[pi];
if (prog->idx == obj->efile.text_shndx) {
name = ".text";
goto skip_search;
}

for (si = 0; si < symbols->d_size / sizeof(GElf_Sym) && !name;
si++) {
Expand Down Expand Up @@ -405,7 +417,7 @@ bpf_object__init_prog_names(struct bpf_object *obj)
prog->section_name);
return -EINVAL;
}

skip_search:
prog->name = strdup(name);
if (!prog->name) {
pr_warning("failed to allocate memory for prog sym %s\n",
Expand Down Expand Up @@ -795,6 +807,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
} else if ((sh.sh_type == SHT_PROGBITS) &&
(sh.sh_flags & SHF_EXECINSTR) &&
(data->d_size > 0)) {
if (strcmp(name, ".text") == 0)
obj->efile.text_shndx = idx;
err = bpf_object__add_program(obj, data->d_buf,
data->d_size, name, idx);
if (err) {
Expand Down Expand Up @@ -856,11 +870,14 @@ bpf_object__find_prog_by_idx(struct bpf_object *obj, int idx)
}

static int
bpf_program__collect_reloc(struct bpf_program *prog,
size_t nr_maps, GElf_Shdr *shdr,
Elf_Data *data, Elf_Data *symbols,
int maps_shndx, struct bpf_map *maps)
bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
Elf_Data *data, struct bpf_object *obj)
{
Elf_Data *symbols = obj->efile.symbols;
int text_shndx = obj->efile.text_shndx;
int maps_shndx = obj->efile.maps_shndx;
struct bpf_map *maps = obj->maps;
size_t nr_maps = obj->nr_maps;
int i, nrels;

pr_debug("collecting relocating info for: '%s'\n",
Expand Down Expand Up @@ -893,8 +910,10 @@ bpf_program__collect_reloc(struct bpf_program *prog,
GELF_R_SYM(rel.r_info));
return -LIBBPF_ERRNO__FORMAT;
}
pr_debug("relo for %ld value %ld name %d\n",
rel.r_info >> 32, sym.st_value, sym.st_name);

if (sym.st_shndx != maps_shndx) {
if (sym.st_shndx != maps_shndx && sym.st_shndx != text_shndx) {
pr_warning("Program '%s' contains non-map related relo data pointing to section %u\n",
prog->section_name, sym.st_shndx);
return -LIBBPF_ERRNO__RELOC;
Expand All @@ -903,6 +922,17 @@ bpf_program__collect_reloc(struct bpf_program *prog,
insn_idx = rel.r_offset / sizeof(struct bpf_insn);
pr_debug("relocation: insn_idx=%u\n", insn_idx);

if (insns[insn_idx].code == (BPF_JMP | BPF_CALL)) {
if (insns[insn_idx].src_reg != BPF_PSEUDO_CALL) {
pr_warning("incorrect bpf_call opcode\n");
return -LIBBPF_ERRNO__RELOC;
}
prog->reloc_desc[i].type = RELO_CALL;
prog->reloc_desc[i].insn_idx = insn_idx;
prog->reloc_desc[i].text_off = sym.st_value;
continue;
}

if (insns[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
pr_warning("bpf: relocation: invalid relo for insns[%d].code 0x%x\n",
insn_idx, insns[insn_idx].code);
Expand All @@ -924,6 +954,7 @@ bpf_program__collect_reloc(struct bpf_program *prog,
return -LIBBPF_ERRNO__RELOC;
}

prog->reloc_desc[i].type = RELO_LD64;
prog->reloc_desc[i].insn_idx = insn_idx;
prog->reloc_desc[i].map_idx = map_idx;
}
Expand Down Expand Up @@ -962,28 +993,77 @@ bpf_object__create_maps(struct bpf_object *obj)
return 0;
}

static int
bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
struct reloc_desc *relo)
{
struct bpf_insn *insn, *new_insn;
struct bpf_program *text;
size_t new_cnt;

if (relo->type != RELO_CALL)
return -LIBBPF_ERRNO__RELOC;

if (prog->idx == obj->efile.text_shndx) {
pr_warning("relo in .text insn %d into off %d\n",
relo->insn_idx, relo->text_off);
return -LIBBPF_ERRNO__RELOC;
}

if (prog->main_prog_cnt == 0) {
text = bpf_object__find_prog_by_idx(obj, obj->efile.text_shndx);
if (!text) {
pr_warning("no .text section found yet relo into text exist\n");
return -LIBBPF_ERRNO__RELOC;
}
new_cnt = prog->insns_cnt + text->insns_cnt;
new_insn = realloc(prog->insns, new_cnt * sizeof(*insn));
if (!new_insn) {
pr_warning("oom in prog realloc\n");
return -ENOMEM;
}
memcpy(new_insn + prog->insns_cnt, text->insns,
text->insns_cnt * sizeof(*insn));
prog->insns = new_insn;
prog->main_prog_cnt = prog->insns_cnt;
prog->insns_cnt = new_cnt;
}
insn = &prog->insns[relo->insn_idx];
insn->imm += prog->main_prog_cnt - relo->insn_idx;
pr_debug("added %zd insn from %s to prog %s\n",
text->insns_cnt, text->section_name, prog->section_name);
return 0;
}

static int
bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
{
int i;
int i, err;

if (!prog || !prog->reloc_desc)
return 0;

for (i = 0; i < prog->nr_reloc; i++) {
int insn_idx, map_idx;
struct bpf_insn *insns = prog->insns;
if (prog->reloc_desc[i].type == RELO_LD64) {
struct bpf_insn *insns = prog->insns;
int insn_idx, map_idx;

insn_idx = prog->reloc_desc[i].insn_idx;
map_idx = prog->reloc_desc[i].map_idx;
insn_idx = prog->reloc_desc[i].insn_idx;
map_idx = prog->reloc_desc[i].map_idx;

if (insn_idx >= (int)prog->insns_cnt) {
pr_warning("relocation out of range: '%s'\n",
prog->section_name);
return -LIBBPF_ERRNO__RELOC;
if (insn_idx >= (int)prog->insns_cnt) {
pr_warning("relocation out of range: '%s'\n",
prog->section_name);
return -LIBBPF_ERRNO__RELOC;
}
insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
insns[insn_idx].imm = obj->maps[map_idx].fd;
} else {
err = bpf_program__reloc_text(prog, obj,
&prog->reloc_desc[i]);
if (err)
return err;
}
insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
insns[insn_idx].imm = obj->maps[map_idx].fd;
}

zfree(&prog->reloc_desc);
Expand Down Expand Up @@ -1026,7 +1106,6 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
Elf_Data *data = obj->efile.reloc[i].data;
int idx = shdr->sh_info;
struct bpf_program *prog;
size_t nr_maps = obj->nr_maps;

if (shdr->sh_type != SHT_REL) {
pr_warning("internal error at %d\n", __LINE__);
Expand All @@ -1040,11 +1119,9 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
return -LIBBPF_ERRNO__RELOC;
}

err = bpf_program__collect_reloc(prog, nr_maps,
err = bpf_program__collect_reloc(prog,
shdr, data,
obj->efile.symbols,
obj->efile.maps_shndx,
obj->maps);
obj);
if (err)
return err;
}
Expand Down Expand Up @@ -1197,6 +1274,8 @@ bpf_object__load_progs(struct bpf_object *obj)
int err;

for (i = 0; i < obj->nr_programs; i++) {
if (obj->programs[i].idx == obj->efile.text_shndx)
continue;
err = bpf_program__load(&obj->programs[i],
obj->license,
obj->kern_version);
Expand Down Expand Up @@ -1859,40 +1938,45 @@ long libbpf_get_error(const void *ptr)
int bpf_prog_load(const char *file, enum bpf_prog_type type,
struct bpf_object **pobj, int *prog_fd)
{
struct bpf_program *prog;
struct bpf_program *prog, *first_prog = NULL;
struct bpf_object *obj;
int err;

obj = bpf_object__open(file);
if (IS_ERR(obj))
return -ENOENT;

prog = bpf_program__next(NULL, obj);
if (!prog) {
bpf_object__close(obj);
return -ENOENT;
}

/*
* If type is not specified, try to guess it based on
* section name.
*/
if (type == BPF_PROG_TYPE_UNSPEC) {
type = bpf_program__guess_type(prog);
bpf_object__for_each_program(prog, obj) {
/*
* If type is not specified, try to guess it based on
* section name.
*/
if (type == BPF_PROG_TYPE_UNSPEC) {
bpf_object__close(obj);
return -EINVAL;
type = bpf_program__guess_type(prog);
if (type == BPF_PROG_TYPE_UNSPEC) {
bpf_object__close(obj);
return -EINVAL;
}
}

bpf_program__set_type(prog, type);
if (prog->idx != obj->efile.text_shndx && !first_prog)
first_prog = prog;
}

if (!first_prog) {
pr_warning("object file doesn't contain bpf program\n");
bpf_object__close(obj);
return -ENOENT;
}

bpf_program__set_type(prog, type);
err = bpf_object__load(obj);
if (err) {
bpf_object__close(obj);
return -EINVAL;
}

*pobj = obj;
*prog_fd = bpf_program__fd(prog);
*prog_fd = bpf_program__fd(first_prog);
return 0;
}

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