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libbpf: Prevent loading vmlinux BTF twice 

Prevent loading/parsing vmlinux BTF twice in some cases: for CO-RE relocations
and for BTF-aware hooks (tp_btf, fentry/fexit, etc).

Fixes: a6ed02cac6 ("libbpf: Load btf_vmlinux only once per object.")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200624043805.1794620-1-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2020-06-23 21:38:05 -07:00 committed by Daniel Borkmann
parent 135c783f47
commit 192b6638ee
1 changed files with 22 additions and 11 deletions
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33
tools/lib/bpf/libbpf.c
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@ -2504,22 +2504,31 @@ static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
static int bpf_object__load_vmlinux_btf(struct bpf_object *obj) static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
{ {
bool need_vmlinux_btf = false;
struct bpf_program *prog; struct bpf_program *prog;
int err; int err;
/* CO-RE relocations need kernel BTF */
if (obj->btf_ext && obj->btf_ext->field_reloc_info.len)
need_vmlinux_btf = true;
bpf_object__for_each_program(prog, obj) { bpf_object__for_each_program(prog, obj) {
if (libbpf_prog_needs_vmlinux_btf(prog)) { if (libbpf_prog_needs_vmlinux_btf(prog)) {
obj->btf_vmlinux = libbpf_find_kernel_btf(); need_vmlinux_btf = true;
if (IS_ERR(obj->btf_vmlinux)) { break;
err = PTR_ERR(obj->btf_vmlinux);
pr_warn("Error loading vmlinux BTF: %d\n", err);
obj->btf_vmlinux = NULL;
return err;
}
return 0;
} }
} }
if (!need_vmlinux_btf)
return 0;
obj->btf_vmlinux = libbpf_find_kernel_btf();
if (IS_ERR(obj->btf_vmlinux)) {
err = PTR_ERR(obj->btf_vmlinux);
pr_warn("Error loading vmlinux BTF: %d\n", err);
obj->btf_vmlinux = NULL;
return err;
}
return 0; return 0;
} }
@ -4945,8 +4954,8 @@ bpf_core_reloc_fields(struct bpf_object *obj, const char *targ_btf_path)
if (targ_btf_path) if (targ_btf_path)
targ_btf = btf__parse_elf(targ_btf_path, NULL); targ_btf = btf__parse_elf(targ_btf_path, NULL);
else else
targ_btf = libbpf_find_kernel_btf(); targ_btf = obj->btf_vmlinux;
if (IS_ERR(targ_btf)) { if (IS_ERR_OR_NULL(targ_btf)) {
pr_warn("failed to get target BTF: %ld\n", PTR_ERR(targ_btf)); pr_warn("failed to get target BTF: %ld\n", PTR_ERR(targ_btf));
return PTR_ERR(targ_btf); return PTR_ERR(targ_btf);
} }
@ -4987,7 +4996,9 @@ bpf_core_reloc_fields(struct bpf_object *obj, const char *targ_btf_path)
} }
out: out:
btf__free(targ_btf); /* obj->btf_vmlinux is freed at the end of object load phase */
if (targ_btf != obj->btf_vmlinux)
btf__free(targ_btf);
if (!IS_ERR_OR_NULL(cand_cache)) { if (!IS_ERR_OR_NULL(cand_cache)) {
hashmap__for_each_entry(cand_cache, entry, i) { hashmap__for_each_entry(cand_cache, entry, i) {
bpf_core_free_cands(entry->value); bpf_core_free_cands(entry->value);