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Date: Fri, 17 Jan 2020 11:02:46 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: KP Singh <kpsingh@...omium.org>
Cc: open list <linux-kernel@...r.kernel.org>,
bpf <bpf@...r.kernel.org>,
Brendan Jackman <jackmanb@...omium.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Anton Protopopov <a.s.protopopov@...il.com>,
Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next] libbpf: Load btf_vmlinux only once per object.
On Fri, Jan 17, 2020 at 8:58 AM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> As more programs (TRACING, STRUCT_OPS, and upcoming LSM) use vmlinux
> BTF information, loading the BTF vmlinux information for every program
> in an object is sub-optimal. The fix was originally proposed in:
>
> https://lore.kernel.org/bpf/CAEf4BzZodr3LKJuM7QwD38BiEH02Cc1UbtnGpVkCJ00Mf+V_Qg@mail.gmail.com/
>
> The btf_vmlinux is populated in the object if any of the programs in
> the object requires it just before the programs are loaded and freed
> after the programs finish loading.
>
> Reported-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Reviewed-by: Brendan Jackman <jackmanb@...omium.org>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
Thanks for the clean up! Few issues, but overall I like this.
> tools/lib/bpf/libbpf.c | 148 +++++++++++++++++++++++++++--------------
> 1 file changed, 97 insertions(+), 51 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 3afaca9bce1d..db0e93882a3b 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -385,6 +385,10 @@ struct bpf_object {
[...]
> @@ -2364,6 +2357,38 @@ static int bpf_object__finalize_btf(struct bpf_object *obj)
> return 0;
> }
>
> +static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
> +{
I suspect that at some point this approach won't be flexible enough,
but it simplifies error handling right now, so I'm ok with it.
> + if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)
> + return true;
> +
> + /* BPF_PROG_TYPE_TRACING programs which do not attach to other programs
> + * also need vmlinux BTF
> + */
> + if (prog->type == BPF_PROG_TYPE_TRACING && !prog->attach_prog_fd)
> + return true;
> +
> + return false;
> +}
> +
> +static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
> +{
> + struct bpf_program *prog;
> +
> + bpf_object__for_each_program(prog, obj) {
> + if (libbpf_prog_needs_vmlinux_btf(prog)) {
> + obj->btf_vmlinux = libbpf_find_kernel_btf();
> + if (IS_ERR(obj->btf_vmlinux)) {
> + pr_warn("vmlinux BTF is not found\n");
please, emit error code as well
also, clear out btf_vmlinux, otherwise your code will attempt to free
invalid pointer later on
> + return -EINVAL;
> + }
> + return 0;
> + }
> + }
> +
> + return 0;
> +}
[...]
> @@ -5280,10 +5301,17 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
> err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
> err = err ? : bpf_object__sanitize_and_load_btf(obj);
> err = err ? : bpf_object__sanitize_maps(obj);
> + err = err ? : bpf_object__load_vmlinux_btf(obj);
> err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
> err = err ? : bpf_object__create_maps(obj);
> err = err ? : bpf_object__relocate(obj, attr->target_btf_path);
> err = err ? : bpf_object__load_progs(obj, attr->log_level);
> +
> + if (obj->btf_vmlinux) {
you can skip this check, btf__free(NULL) is handled properly as noop
> + btf__free(obj->btf_vmlinux);
> + obj->btf_vmlinux = NULL;
> + }
> +
> if (err)
> goto out;
[...]
> +
> +static inline int __find_vmlinux_btf_id(struct btf *btf, const char *name,
> + enum bpf_attach_type attach_type)
> +{
> + int err;
> +
> + if (attach_type == BPF_TRACE_RAW_TP)
> + err = find_btf_by_prefix_kind(btf, BTF_TRACE_PREFIX, name,
> + BTF_KIND_TYPEDEF);
> + else
> + err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
> +
> + return err;
> +}
> +
> int libbpf_find_vmlinux_btf_id(const char *name,
> enum bpf_attach_type attach_type)
> {
> struct btf *btf = libbpf_find_kernel_btf();
I had complaints previously about doing too much heavy-lifting in
variable assignment, not sure why this slipped through. Can you please
split this into variable declaration and separate assignment below?
> - char raw_tp_btf[128] = BTF_PREFIX;
> - char *dst = raw_tp_btf + sizeof(BTF_PREFIX) - 1;
> - const char *btf_name;
> - int err = -EINVAL;
> - __u32 kind;
>
> if (IS_ERR(btf)) {
> pr_warn("vmlinux BTF is not found\n");
> return -EINVAL;
> }
>
> - if (attach_type == BPF_TRACE_RAW_TP) {
> - /* prepend "btf_trace_" prefix per kernel convention */
> - strncat(dst, name, sizeof(raw_tp_btf) - sizeof(BTF_PREFIX));
> - btf_name = raw_tp_btf;
> - kind = BTF_KIND_TYPEDEF;
> - } else {
> - btf_name = name;
> - kind = BTF_KIND_FUNC;
> - }
> - err = btf__find_by_name_kind(btf, btf_name, kind);
> - btf__free(btf);
> - return err;
> + return __find_vmlinux_btf_id(btf, name, attach_type);
> }
>
> static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
> @@ -6567,10 +6612,11 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
> return err;
> }
>
> -static int libbpf_find_attach_btf_id(const char *name,
> - enum bpf_attach_type attach_type,
> - __u32 attach_prog_fd)
> +static int libbpf_find_attach_btf_id(struct bpf_program *prog)
> {
> + enum bpf_attach_type attach_type = prog->expected_attach_type;
> + __u32 attach_prog_fd = prog->attach_prog_fd;
> + const char *name = prog->section_name;
> int i, err;
>
> if (!name)
> @@ -6585,8 +6631,8 @@ static int libbpf_find_attach_btf_id(const char *name,
> err = libbpf_find_prog_btf_id(name + section_defs[i].len,
> attach_prog_fd);
> else
> - err = libbpf_find_vmlinux_btf_id(name + section_defs[i].len,
> - attach_type);
> + err = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
> + name + section_defs[i].len, attach_type);
argument indentation is off here, please fix
> if (err <= 0)
> pr_warn("%s is not found in vmlinux BTF\n", name);
> return err;
> --
> 2.20.1
>
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