> On Oct 13, 2021, at 12:33 AM, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> This uses the bpf_kallsyms_lookup_name helper added in previous patches
> to relocate typeless ksyms. The return value ENOENT can be ignored, and
> the value written to 'res' can be directly stored to the insn, as it is
> overwritten to 0 on lookup failure. For repeating symbols, we can simply
> copy the previously populated bpf_insn.
>
> Also, we need to take care to not close fds for typeless ksym_desc, so
> reuse the 'off' member's space to add a marker for typeless ksym and use
> that to skip them in cleanup_relos.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
[...]
> }
>
> +/* Expects:
> + * BPF_REG_8 - pointer to instruction
> + */
> +static void emit_relo_ksym_typeless(struct bpf_gen *gen,
> + struct ksym_relo_desc *relo, int insn)
This function has quite some duplicated logic as emit_relo_ksym_btf().
I guess we can somehow reuse the code here. Say, we pull changes from
3/8 first to handle weak type. Then we extend the function to handle
typeless. Would this work?
> +{
> + struct ksym_desc *kdesc;
> +
> + kdesc = get_ksym_desc(gen, relo);
> + if (!kdesc)
> + return;
> + /* try to copy from existing ldimm64 insn */
> + if (kdesc->ref > 1) {
> + move_blob2blob(gen, insn + offsetof(struct bpf_insn, imm), 4,
> + kdesc->insn + offsetof(struct bpf_insn, imm));
> + move_blob2blob(gen, insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm), 4,
> + kdesc->insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm));
> + goto log;
> + }
> + /* remember insn offset, so we can copy ksym addr later */
> + kdesc->insn = insn;
> + /* skip typeless ksym_desc in fd closing loop in cleanup_relos */
> + kdesc->typeless = true;
> + emit_bpf_kallsyms_lookup_name(gen, relo);
> + emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_7, -ENOENT, 1));
> + emit_check_err(gen);
> + /* store lower half of addr into insn[insn_idx].imm */
> + emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_9, offsetof(struct bpf_insn, imm)));
> + /* store upper half of addr into insn[insn_idx + 1].imm */
> + emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32));
> + emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_9,
> + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm)));
> +log:
> + if (!gen->log_level)
> + return;
> + emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_8,
> + offsetof(struct bpf_insn, imm)));
> + emit(gen, BPF_LDX_MEM(BPF_H, BPF_REG_9, BPF_REG_8, sizeof(struct bpf_insn) +
> + offsetof(struct bpf_insn, imm)));
> + debug_regs(gen, BPF_REG_7, BPF_REG_9, " var t=0 w=%d (%s:count=%d): imm[0]: %%d, imm[1]: %%d",
> + relo->is_weak, relo->name, kdesc->ref);
> + emit(gen, BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_8, offsetofend(struct bpf_insn, code)));
> + debug_regs(gen, BPF_REG_9, -1, " var t=0 w=%d (%s:count=%d): insn.reg",
> + relo->is_weak, relo->name, kdesc->ref);
>
[...]
> +++ b/tools/lib/bpf/libbpf.c
> @@ -6355,17 +6355,14 @@ static int bpf_program__record_externs(struct bpf_program *prog)
> case RELO_EXTERN_VAR:
> if (ext->type != EXT_KSYM)
> continue;
> - if (!ext->ksym.type_id) {
> - pr_warn("typeless ksym %s is not supported yet\n",
> - ext->name);
> - return -ENOTSUP;
> - }
> - bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
> + bpf_gen__record_extern(obj->gen_loader, ext->name,
> + ext->is_weak, !ext->ksym.type_id,
> BTF_KIND_VAR, relo->insn_idx);
> break;
> case RELO_EXTERN_FUNC:
> - bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
> - BTF_KIND_FUNC, relo->insn_idx);
> + bpf_gen__record_extern(obj->gen_loader, ext->name,
> + ext->is_weak, 0, BTF_KIND_FUNC,
nit: Prefer use "false" for bool arguments.
> + relo->insn_idx);
> break;
> default:
> continue;
> --
> 2.33.0
>
