libbpf: Support kfunc detection in light skeleton.

Teach gen_loader to find {btf_id, btf_obj_fd} of kernel variables and kfuncs
and populate corresponding ld_imm64 and bpf_call insns.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230321203854.3035-4-alexei.starovoitov@gmail.com

diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
index 2233089..fdf4440 100644 (file)
--- a/tools/lib/bpf/bpf_gen_internal.h
+++ b/tools/lib/bpf/bpf_gen_internal.h
@@ -11,6 +11,7 @@ struct ksym_relo_desc {
        int insn_idx;
        bool is_weak;
        bool is_typeless;
+       bool is_ld64;
 };
 
 struct ksym_desc {
@@ -24,6 +25,7 @@ struct ksym_desc {
                bool typeless;
        };
        int insn;
+       bool is_ld64;
 };
 
 struct bpf_gen {
@@ -65,7 +67,7 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *value, __u
 void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx);
 void bpf_gen__record_attach_target(struct bpf_gen *gen, const char *name, enum bpf_attach_type type);
 void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
-                           bool is_typeless, int kind, int insn_idx);
+                           bool is_typeless, bool is_ld64, int kind, int insn_idx);
 void bpf_gen__record_relo_core(struct bpf_gen *gen, const struct bpf_core_relo *core_relo);
 void bpf_gen__populate_outer_map(struct bpf_gen *gen, int outer_map_idx, int key, int inner_map_idx);
 

diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index b74c82b..83e8e3b 100644 (file)
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -560,7 +560,7 @@ static void emit_find_attach_target(struct bpf_gen *gen)
 }
 
 void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
-                           bool is_typeless, int kind, int insn_idx)
+                           bool is_typeless, bool is_ld64, int kind, int insn_idx)
 {
        struct ksym_relo_desc *relo;
 
@@ -574,6 +574,7 @@ void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
        relo->name = name;
        relo->is_weak = is_weak;
        relo->is_typeless = is_typeless;
+       relo->is_ld64 = is_ld64;
        relo->kind = kind;
        relo->insn_idx = insn_idx;
        gen->relo_cnt++;
@@ -586,9 +587,11 @@ static struct ksym_desc *get_ksym_desc(struct bpf_gen *gen, struct ksym_relo_des
        int i;
 
        for (i = 0; i < gen->nr_ksyms; i++) {
-               if (!strcmp(gen->ksyms[i].name, relo->name)) {
-                       gen->ksyms[i].ref++;
-                       return &gen->ksyms[i];
+               kdesc = &gen->ksyms[i];
+               if (kdesc->kind == relo->kind && kdesc->is_ld64 == relo->is_ld64 &&
+                   !strcmp(kdesc->name, relo->name)) {
+                       kdesc->ref++;
+                       return kdesc;
                }
        }
        kdesc = libbpf_reallocarray(gen->ksyms, gen->nr_ksyms + 1, sizeof(*kdesc));
@@ -603,6 +606,7 @@ static struct ksym_desc *get_ksym_desc(struct bpf_gen *gen, struct ksym_relo_des
        kdesc->ref = 1;
        kdesc->off = 0;
        kdesc->insn = 0;
+       kdesc->is_ld64 = relo->is_ld64;
        return kdesc;
 }
 
@@ -864,23 +868,17 @@ static void emit_relo(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insn
 {
        int insn;
 
-       pr_debug("gen: emit_relo (%d): %s at %d\n", relo->kind, relo->name, relo->insn_idx);
+       pr_debug("gen: emit_relo (%d): %s at %d %s\n",
+                relo->kind, relo->name, relo->insn_idx, relo->is_ld64 ? "ld64" : "call");
        insn = insns + sizeof(struct bpf_insn) * relo->insn_idx;
        emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_8, BPF_PSEUDO_MAP_IDX_VALUE, 0, 0, 0, insn));
-       switch (relo->kind) {
-       case BTF_KIND_VAR:
+       if (relo->is_ld64) {
                if (relo->is_typeless)
                        emit_relo_ksym_typeless(gen, relo, insn);
                else
                        emit_relo_ksym_btf(gen, relo, insn);
-               break;
-       case BTF_KIND_FUNC:
+       } else {
                emit_relo_kfunc_btf(gen, relo, insn);
-               break;
-       default:
-               pr_warn("Unknown relocation kind '%d'\n", relo->kind);
-               gen->error = -EDOM;
-               return;
        }
 }
 
@@ -903,18 +901,20 @@ static void cleanup_core_relo(struct bpf_gen *gen)
 
 static void cleanup_relos(struct bpf_gen *gen, int insns)
 {
+       struct ksym_desc *kdesc;
        int i, insn;
 
        for (i = 0; i < gen->nr_ksyms; i++) {
+               kdesc = &gen->ksyms[i];
                /* only close fds for typed ksyms and kfuncs */
-               if (gen->ksyms[i].kind == BTF_KIND_VAR && !gen->ksyms[i].typeless) {
+               if (kdesc->is_ld64 && !kdesc->typeless) {
                        /* close fd recorded in insn[insn_idx + 1].imm */
-                       insn = gen->ksyms[i].insn;
+                       insn = kdesc->insn;
                        insn += sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm);
                        emit_sys_close_blob(gen, insn);
-               } else if (gen->ksyms[i].kind == BTF_KIND_FUNC) {
-                       emit_sys_close_blob(gen, blob_fd_array_off(gen, gen->ksyms[i].off));
-                       if (gen->ksyms[i].off < MAX_FD_ARRAY_SZ)
+               } else if (!kdesc->is_ld64) {
+                       emit_sys_close_blob(gen, blob_fd_array_off(gen, kdesc->off));
+                       if (kdesc->off < MAX_FD_ARRAY_SZ)
                                gen->nr_fd_array--;
                }
        }

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f8131f9..5d32aa8 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7070,18 +7070,21 @@ static int bpf_program_record_relos(struct bpf_program *prog)
        for (i = 0; i < prog->nr_reloc; i++) {
                struct reloc_desc *relo = &prog->reloc_desc[i];
                struct extern_desc *ext = &obj->externs[relo->sym_off];
+               int kind;
 
                switch (relo->type) {
                case RELO_EXTERN_LD64:
                        if (ext->type != EXT_KSYM)
                                continue;
+                       kind = btf_is_var(btf__type_by_id(obj->btf, ext->btf_id)) ?
+                               BTF_KIND_VAR : BTF_KIND_FUNC;
                        bpf_gen__record_extern(obj->gen_loader, ext->name,
                                               ext->is_weak, !ext->ksym.type_id,
-                                              BTF_KIND_VAR, relo->insn_idx);
+                                              true, kind, relo->insn_idx);
                        break;
                case RELO_EXTERN_CALL:
                        bpf_gen__record_extern(obj->gen_loader, ext->name,
-                                              ext->is_weak, false, BTF_KIND_FUNC,
+                                              ext->is_weak, false, false, BTF_KIND_FUNC,
                                               relo->insn_idx);
                        break;
                case RELO_CORE: {