netdev - Re: [PATCH bpf-next 11/15] libbpf: Record extern sym relocation first

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Date:   Thu, 18 Mar 2021 20:16:50 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 11/15] libbpf: Record extern sym relocation first

On Tue, Mar 16, 2021 at 12:02 AM Martin KaFai Lau <kafai@...com> wrote:
>
> This patch records the extern sym relocs first before recording
> subprog relocs.  The later patch will have relocs for extern
> kernel function call which is also using BPF_JMP | BPF_CALL.
> It will be easier to handle the extern symbols first in
> the later patch.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---

Looks good, just let's add that tiny helper for cleanliness and to
match what we do for ldimm64

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  tools/lib/bpf/libbpf.c | 50 +++++++++++++++++++++---------------------
>  1 file changed, 25 insertions(+), 25 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 8f924aece736..0a60fcb2fba2 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3416,31 +3416,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
>
>         reloc_desc->processed = false;
>
> -       /* sub-program call relocation */
> -       if (insn->code == (BPF_JMP | BPF_CALL)) {
> -               if (insn->src_reg != BPF_PSEUDO_CALL) {
> -                       pr_warn("prog '%s': incorrect bpf_call opcode\n", prog->name);
> -                       return -LIBBPF_ERRNO__RELOC;
> -               }
> -               /* text_shndx can be 0, if no default "main" program exists */
> -               if (!shdr_idx || shdr_idx != obj->efile.text_shndx) {
> -                       sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
> -                       pr_warn("prog '%s': bad call relo against '%s' in section '%s'\n",
> -                               prog->name, sym_name, sym_sec_name);
> -                       return -LIBBPF_ERRNO__RELOC;
> -               }
> -               if (sym->st_value % BPF_INSN_SZ) {
> -                       pr_warn("prog '%s': bad call relo against '%s' at offset %zu\n",
> -                               prog->name, sym_name, (size_t)sym->st_value);
> -                       return -LIBBPF_ERRNO__RELOC;
> -               }
> -               reloc_desc->type = RELO_CALL;
> -               reloc_desc->insn_idx = insn_idx;
> -               reloc_desc->sym_off = sym->st_value;
> -               return 0;
> -       }
> -
> -       if (!is_ldimm64(insn)) {
> +       if (insn->code != (BPF_JMP | BPF_CALL) && !is_ldimm64(insn)) {
>                 pr_warn("prog '%s': invalid relo against '%s' for insns[%d].code 0x%x\n",
>                         prog->name, sym_name, insn_idx, insn->code);
>                 return -LIBBPF_ERRNO__RELOC;
> @@ -3469,6 +3445,30 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
>                 return 0;
>         }
>
> +       /* sub-program call relocation */
> +       if (insn->code == (BPF_JMP | BPF_CALL)) {

can you please add is_call_insn() helper checking this, similarly to
how we now have is_ldimm64() (should probably be is_ldimm64_insn() for
consistency)

> +               if (insn->src_reg != BPF_PSEUDO_CALL) {
> +                       pr_warn("prog '%s': incorrect bpf_call opcode\n", prog->name);
> +                       return -LIBBPF_ERRNO__RELOC;
> +               }
> +               /* text_shndx can be 0, if no default "main" program exists */
> +               if (!shdr_idx || shdr_idx != obj->efile.text_shndx) {
> +                       sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
> +                       pr_warn("prog '%s': bad call relo against '%s' in section '%s'\n",
> +                               prog->name, sym_name, sym_sec_name);
> +                       return -LIBBPF_ERRNO__RELOC;
> +               }
> +               if (sym->st_value % BPF_INSN_SZ) {
> +                       pr_warn("prog '%s': bad call relo against '%s' at offset %zu\n",
> +                               prog->name, sym_name, (size_t)sym->st_value);
> +                       return -LIBBPF_ERRNO__RELOC;
> +               }
> +               reloc_desc->type = RELO_CALL;
> +               reloc_desc->insn_idx = insn_idx;
> +               reloc_desc->sym_off = sym->st_value;
> +               return 0;
> +       }
> +
>         if (!shdr_idx || shdr_idx >= SHN_LORESERVE) {
>                 pr_warn("prog '%s': invalid relo against '%s' in special section 0x%x; forgot to initialize global var?..\n",
>                         prog->name, sym_name, shdr_idx);
> --
> 2.30.2
>