On 17/06/2019 21:40, Jiong Wang wrote:
> Now if we don't split patch when patch an insn inside patch, instead, if we
> replace the patched insn using what you suggested, then the logic looks to
> me becomes even more complex, something like
>
> for (idx = 0; idx < insn_cnt; idx++) {
> if (insns[idx] is not BPF_LIST_INSN) {
> do_insn(...)
> }
> else if (insns[idx] is BPF_LIST_INSN) {
> list = pool_base + insn.imm;
> while (list) {
> insn = list_head->insn;
> if (insn is BF_LIST_INSN) {
> sub_list = ...
> while ()
> do_insn()
> continue;
> }
> do_insn(...)
> list = pool_base + list->next;
> }
> }
> }
Why can't do_insn() just go like:
if (insn is BPF_LIST_INSN)
for (idx = 0; idx < LIST_COUNT(insn); idx++)
do_insn(pool_base + LIST_START(insn) + idx);
else
rest of processing
?
Alternatively, iterate with something more sophisticated than 'idx++'
(standard recursion-to-loop transformation).
You shouldn't ever need a for() tower statically in the code...
> So, I am thinking what Alexei and Andrii suggested make sense, just use
> single data structure (singly linked list) to represent everything, so the
> insn traversal etc could be simple
But then you have to also store orig_insn_idx with each insn, so you can
calculate the new jump offsets when you linearise. Having an array of
patched_orig_insns gives you that for free.
