> On Oct 14, 2021, at 10:53 AM, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> On Thu, Oct 14, 2021 at 10:09:43PM IST, Song Liu wrote:
>>
>>
>>> 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?
>>
>
> Ok, will put both into the same function in the next version. Though the part
> between:
>
>>> +{
>>> + 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));
>
> this and ...
>
>>> + 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)));
>
> ... this won't overlap (so it will have to jump into the else branch to clear_src_reg).
>
> e.g. it looks something like this:
>
> if (kdesc->ref > 1) {
> move...
> if (!relo->is_typeless)
> ...
> goto clear_src_reg;
> }
> kdesc->insn = insn;
> ...
> if (relo->is_typeless) {
> ...
> } else {
> ...
> clear_src_reg:
> ...
> }
>
> so it looked better to split into separate functions (maybe we can just move the
> logging part to common helper? the rest is just duplicating the inital get and
> move_blob2blob).
Yeah, I can tell it not very clean either way. A common helper might be the best
option here.
Thanks,
Song
