From: Yonghong Song <yhs@fb.com>
To: Andrii Nakryiko <andrii@kernel.org>, <bpf@vger.kernel.org>,
<netdev@vger.kernel.org>, <ast@fb.com>, <daniel@iogearbox.net>
Cc: <kernel-team@fb.com>, Hao Luo <haoluo@google.com>
Subject: Re: [PATCH v2 bpf-next 6/7] libbpf: support kernel module ksym externs
Date: Sun, 10 Jan 2021 20:15:12 -0800 [thread overview]
Message-ID: <dc1a06fe-f957-deb8-772c-b4c65042c3b3@fb.com> (raw)
In-Reply-To: <20210108220930.482456-7-andrii@kernel.org>
On 1/8/21 2:09 PM, Andrii Nakryiko wrote:
> Add support for searching for ksym externs not just in vmlinux BTF, but across
> all module BTFs, similarly to how it's done for CO-RE relocations. Kernels
> that expose module BTFs through sysfs are assumed to support new ldimm64
> instruction extension with BTF FD provided in insn[1].imm field, so no extra
> feature detection is performed.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
> tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++---------------
> 1 file changed, 30 insertions(+), 17 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6ae748f6ea11..57559a71e4de 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -395,7 +395,8 @@ struct extern_desc {
> unsigned long long addr;
>
> /* target btf_id of the corresponding kernel var. */
> - int vmlinux_btf_id;
> + int kernel_btf_obj_fd;
> + int kernel_btf_id;
>
> /* local btf_id of the ksym extern's type. */
> __u32 type_id;
> @@ -6162,7 +6163,8 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
> } else /* EXT_KSYM */ {
> if (ext->ksym.type_id) { /* typed ksyms */
> insn[0].src_reg = BPF_PSEUDO_BTF_ID;
> - insn[0].imm = ext->ksym.vmlinux_btf_id;
> + insn[0].imm = ext->ksym.kernel_btf_id;
> + insn[1].imm = ext->ksym.kernel_btf_obj_fd;
> } else { /* typeless ksyms */
> insn[0].imm = (__u32)ext->ksym.addr;
> insn[1].imm = ext->ksym.addr >> 32;
> @@ -7319,7 +7321,8 @@ static int bpf_object__read_kallsyms_file(struct bpf_object *obj)
> static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> {
> struct extern_desc *ext;
> - int i, id;
> + struct btf *btf;
> + int i, j, id, btf_fd, err;
>
> for (i = 0; i < obj->nr_extern; i++) {
> const struct btf_type *targ_var, *targ_type;
> @@ -7331,8 +7334,22 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> if (ext->type != EXT_KSYM || !ext->ksym.type_id)
> continue;
>
> - id = btf__find_by_name_kind(obj->btf_vmlinux, ext->name,
> - BTF_KIND_VAR);
> + btf = obj->btf_vmlinux;
> + btf_fd = 0;
> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
> + if (id == -ENOENT) {
> + err = load_module_btfs(obj);
> + if (err)
> + return err;
> +
> + for (j = 0; j < obj->btf_module_cnt; j++) {
> + btf = obj->btf_modules[j].btf;
> + btf_fd = obj->btf_modules[j].fd;
Do we have possibility btf_fd == 0 here?
> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
> + if (id != -ENOENT)
> + break;
> + }
> + }
> if (id <= 0) {
> pr_warn("extern (ksym) '%s': failed to find BTF ID in vmlinux BTF.\n",
> ext->name);
> @@ -7343,24 +7360,19 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> local_type_id = ext->ksym.type_id;
>
> /* find target type_id */
> - targ_var = btf__type_by_id(obj->btf_vmlinux, id);
> - targ_var_name = btf__name_by_offset(obj->btf_vmlinux,
> - targ_var->name_off);
> - targ_type = skip_mods_and_typedefs(obj->btf_vmlinux,
> - targ_var->type,
> - &targ_type_id);
> + targ_var = btf__type_by_id(btf, id);
> + targ_var_name = btf__name_by_offset(btf, targ_var->name_off);
> + targ_type = skip_mods_and_typedefs(btf, targ_var->type, &targ_type_id);
>
> ret = bpf_core_types_are_compat(obj->btf, local_type_id,
> - obj->btf_vmlinux, targ_type_id);
> + btf, targ_type_id);
> if (ret <= 0) {
> const struct btf_type *local_type;
> const char *targ_name, *local_name;
>
> local_type = btf__type_by_id(obj->btf, local_type_id);
> - local_name = btf__name_by_offset(obj->btf,
> - local_type->name_off);
> - targ_name = btf__name_by_offset(obj->btf_vmlinux,
> - targ_type->name_off);
> + local_name = btf__name_by_offset(obj->btf, local_type->name_off);
> + targ_name = btf__name_by_offset(btf, targ_type->name_off);
>
> pr_warn("extern (ksym) '%s': incompatible types, expected [%d] %s %s, but kernel has [%d] %s %s\n",
> ext->name, local_type_id,
> @@ -7370,7 +7382,8 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
> }
>
> ext->is_set = true;
> - ext->ksym.vmlinux_btf_id = id;
> + ext->ksym.kernel_btf_obj_fd = btf_fd;
> + ext->ksym.kernel_btf_id = id;
> pr_debug("extern (ksym) '%s': resolved to [%d] %s %s\n",
> ext->name, id, btf_kind_str(targ_var), targ_var_name);
> }
>
next prev parent reply other threads:[~2021-01-11 4:16 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 22:09 [PATCH v2 bpf-next 0/7] Support kernel module ksym variables Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 1/7] bpf: add bpf_patch_call_args prototype to include/linux/bpf.h Andrii Nakryiko
2021-01-11 4:02 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 2/7] bpf: avoid warning when re-casting __bpf_call_base into __bpf_call_base_args Andrii Nakryiko
2021-01-11 4:03 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 3/7] bpf: declare __bpf_free_used_maps() unconditionally Andrii Nakryiko
2021-01-11 4:03 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 4/7] selftests/bpf: sync RCU before unloading bpf_testmod Andrii Nakryiko
2021-01-11 4:05 ` Yonghong Song
2021-01-11 18:59 ` Hao Luo
2021-01-08 22:09 ` [PATCH v2 bpf-next 5/7] bpf: support BPF ksym variables in kernel modules Andrii Nakryiko
2021-01-11 4:13 ` Yonghong Song
2021-01-11 21:29 ` Andrii Nakryiko
2021-01-12 1:25 ` Yonghong Song
2021-01-11 18:59 ` Hao Luo
2021-01-11 21:31 ` Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 6/7] libbpf: support kernel module ksym externs Andrii Nakryiko
2021-01-11 4:15 ` Yonghong Song [this message]
2021-01-11 21:37 ` Andrii Nakryiko
2021-01-12 1:34 ` Yonghong Song
2021-01-12 6:45 ` Andrii Nakryiko
2021-01-11 19:00 ` Hao Luo
2021-01-11 21:39 ` Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 7/7] selftests/bpf: test " Andrii Nakryiko
2021-01-11 4:18 ` Yonghong Song
2021-01-11 21:40 ` Andrii Nakryiko
2021-01-11 19:00 ` Hao Luo
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