[PATCH bpf-next 5/8] libbpf: support local function pointer relocation
From: Yonghong Song <hidden>
Date: 2021-02-04 23:49:23
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [library] (libbpf), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
A new relocation RELO_LOCAL_FUNC is added to capture local (static) function pointers loaded with ld_imm64 insns. Such ld_imm64 insns are marked with BPF_PSEUDO_FUNC and will be passed to kernel so kernel can replace them with proper actual jited func addresses. Signed-off-by: Yonghong Song <redacted> --- tools/lib/bpf/libbpf.c | 33 ++++++++++++++++++++++++++++++--- 1 file changed, 30 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2abbc3800568..a5146c9e3e06 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c@@ -188,6 +188,7 @@ enum reloc_type { RELO_CALL, RELO_DATA, RELO_EXTERN, + RELO_LOCAL_FUNC, }; struct reloc_desc {
@@ -574,6 +575,12 @@ static bool insn_is_subprog_call(const struct bpf_insn *insn) insn->off == 0; } +static bool insn_is_pseudo_func(const struct bpf_insn *insn) +{ + return insn->code == (BPF_LD | BPF_IMM | BPF_DW) && + 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,
@@ -3395,6 +3402,16 @@ static int bpf_program__record_reloc(struct bpf_program *prog, return 0; } + if (insn->code == (BPF_LD | BPF_IMM | BPF_DW) && + GELF_ST_BIND(sym->st_info) == STB_LOCAL && + GELF_ST_TYPE(sym->st_info) == STT_SECTION && + shdr_idx == obj->efile.text_shndx) { + reloc_desc->type = RELO_LOCAL_FUNC; + reloc_desc->insn_idx = insn_idx; + reloc_desc->sym_off = sym->st_value; + return 0; + } + if (insn->code != (BPF_LD | BPF_IMM | BPF_DW)) { pr_warn("prog '%s': invalid relo against '%s' for insns[%d].code 0x%x\n", prog->name, sym_name, insn_idx, insn->code);
@@ -6172,6 +6189,9 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) } relo->processed = true; break; + case RELO_LOCAL_FUNC: + insn[0].src_reg = BPF_PSEUDO_FUNC; + /* fallthrough */ case RELO_CALL: /* will be handled as a follow up pass */ break;
@@ -6358,11 +6378,11 @@ 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_LOCAL_FUNC) { pr_warn("prog '%s': unexpected relo for insn #%zu, type %d\n", prog->name, insn_idx, relo->type); return -LIBBPF_ERRNO__RELOC;
@@ -6374,8 +6394,15 @@ 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 local func relocation, the imm field encodes + * 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 / BPF_INSN_SZ + + insn->imm / BPF_INSN_SZ + 1; } else { /* if subprogram call is to a static function within * the same ELF section, there won't be any relocation
--
2.24.1