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SubjectRe: [PATCH bpf-next v1 1/8] bpf: Introduce pseudo_btf_id
On Wed, Aug 19, 2020 at 03:40:23PM -0700, Hao Luo wrote:
> +
> /* verify BPF_LD_IMM64 instruction */
> static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
> {
> @@ -7234,6 +7296,9 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
> return 0;
> }
>
> + if (insn->src_reg == BPF_PSEUDO_BTF_ID)
> + return check_pseudo_btf_id(env, insn);
> +
> map = env->used_maps[aux->map_index];
> mark_reg_known_zero(env, regs, insn->dst_reg);
> regs[insn->dst_reg].map_ptr = map;
> @@ -9255,6 +9320,9 @@ static int replace_map_fd_with_map_ptr(struct bpf_verifier_env *env)
> /* valid generic load 64-bit imm */
> goto next_insn;
>
> + if (insn[0].src_reg == BPF_PSEUDO_BTF_ID)
> + goto next_insn;
> +

Why did you choose to do it during main do_check() walk instead of this pre-pass ?
check_ld_imm() can be called multiple times for the same insn,
so it's faster and less surprising to do it during replace_map_fd_with_map_ptr().
BTF needs to be parsed first, of course.
You can either move check_btf_info() before replace_map_fd_with_map_ptr() or
move replace_map_fd_with_map_ptr() after check_btf_info().
The latter is probably cleaner.

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