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libbpf: Support subprog address relocation 

A new relocation RELO_SUBPROG_ADDR is added to capture
subprog addresses loaded with ld_imm64 insns. Such ld_imm64
insns are marked with BPF_PSEUDO_FUNC and will be passed to
kernel. For bpf_for_each_map_elem() case, kernel will
check that the to-be-used subprog address must be a static
function and replace it with proper actual jited func address.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210226204930.3885367-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2021-02-26 12:49:30 -08:00 committed by Alexei Starovoitov
parent b8f871fa32
commit 53eddb5e04
1 changed files with 61 additions and 3 deletions
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64
tools/lib/bpf/libbpf.c
View File

@ -188,6 +188,7 @@ enum reloc_type {
RELO_CALL,
RELO_DATA,
RELO_EXTERN,
RELO_SUBPROG_ADDR,
};
struct reloc_desc {
@ -579,6 +580,11 @@ static bool is_ldimm64(struct bpf_insn *insn)
return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
}
static bool insn_is_pseudo_func(struct bpf_insn *insn)
{
return is_ldimm64(insn) && insn->src_reg == BPF_PSEUDO_FUNC;
}
static int
bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog,
const char *name, size_t sec_idx, const char *sec_name,
@ -2979,6 +2985,23 @@ static bool sym_is_extern(const GElf_Sym *sym)
GELF_ST_TYPE(sym->st_info) == STT_NOTYPE;
}
static bool sym_is_subprog(const GElf_Sym *sym, int text_shndx)
{
int bind = GELF_ST_BIND(sym->st_info);
int type = GELF_ST_TYPE(sym->st_info);
/* in .text section */
if (sym->st_shndx != text_shndx)
return false;
/* local function */
if (bind == STB_LOCAL && type == STT_SECTION)
return true;
/* global function */
return bind == STB_GLOBAL && type == STT_FUNC;
}
static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
{
const struct btf_type *t;
@ -3435,6 +3458,23 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
return -LIBBPF_ERRNO__RELOC;
}
/* loading subprog addresses */
if (sym_is_subprog(sym, obj->efile.text_shndx)) {
/* global_func: sym->st_value = offset in the section, insn->imm = 0.
* local_func: sym->st_value = 0, insn->imm = offset in the section.
*/
if ((sym->st_value % BPF_INSN_SZ) || (insn->imm % BPF_INSN_SZ)) {
pr_warn("prog '%s': bad subprog addr relo against '%s' at offset %zu+%d\n",
prog->name, sym_name, (size_t)sym->st_value, insn->imm);
return -LIBBPF_ERRNO__RELOC;
}
reloc_desc->type = RELO_SUBPROG_ADDR;
reloc_desc->insn_idx = insn_idx;
reloc_desc->sym_off = sym->st_value;
return 0;
}
type = bpf_object__section_to_libbpf_map_type(obj, shdr_idx);
sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
@ -6172,6 +6212,10 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
}
relo->processed = true;
break;
case RELO_SUBPROG_ADDR:
insn[0].src_reg = BPF_PSEUDO_FUNC;
/* will be handled as a follow up pass */
break;
case RELO_CALL:
/* will be handled as a follow up pass */
break;
@ -6358,11 +6402,11 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
for (insn_idx = 0; insn_idx < prog->sec_insn_cnt; insn_idx++) {
insn = &main_prog->insns[prog->sub_insn_off + insn_idx];
if (!insn_is_subprog_call(insn))
if (!insn_is_subprog_call(insn) && !insn_is_pseudo_func(insn))
continue;
relo = find_prog_insn_relo(prog, insn_idx);
if (relo && relo->type != RELO_CALL) {
if (relo && relo->type != RELO_CALL && relo->type != RELO_SUBPROG_ADDR) {
pr_warn("prog '%s': unexpected relo for insn #%zu, type %d\n",
prog->name, insn_idx, relo->type);
return -LIBBPF_ERRNO__RELOC;
@ -6374,8 +6418,22 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
* call always has imm = -1, but for static functions
* relocation is against STT_SECTION and insn->imm
* points to a start of a static function
*
* for subprog addr relocation, the relo->sym_off + insn->imm is
* the byte offset in the corresponding section.
*/
sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
if (relo->type == RELO_CALL)
sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
else
sub_insn_idx = (relo->sym_off + insn->imm) / BPF_INSN_SZ;
} else if (insn_is_pseudo_func(insn)) {
/*
* RELO_SUBPROG_ADDR relo is always emitted even if both
* functions are in the same section, so it shouldn't reach here.
*/
pr_warn("prog '%s': missing subprog addr relo for insn #%zu\n",
prog->name, insn_idx);
return -LIBBPF_ERRNO__RELOC;
} else {
/* if subprogram call is to a static function within
* the same ELF section, there won't be any relocation