On Thu, Apr 05, 2018 at 04:50:03PM +0100, Jiong Wang wrote:
> On 03/04/2018 02:08, Alexei Starovoitov wrote:
> > Combining subprog pass with do_check is going into opposite direction
> > of this long term work. Divide and conquer. Combining more things into
> > do_check is the opposite of this programming principle.
>
> Agree. And for the redundant insn traversal issue in check_subprogs that
> Edward trying to fix, I am thinking we could do it by utilizing the
> existing DFS traversal in check_cfg.
>
> The current DFS probably could be improved into an generic instruction
> information collection pass.
>
> This won't make the existing DFS complexer as it only does information
> collection as a side job during traversal. These collected information
> then could be used to build any other information to be consumed later,
> for example subprog, basic blocks etc.
>
> For the redundant insn traversal issue during subprog detection, the
> Like how we mark STATE_LIST_MARK in DFS, we could just call add_subprog
> for BPF_PSEUDO_CALL insn during DFS.
>
> i.e we change the code logic of check_cfg into:
>
> check_cfg
> {
> * DFS traversal:
> - detect back-edge.
> - collect STATE_LIST_MARK.
> - collect subprog destination.
>
> * check all insns are reachable.
> * check_subprogs (insn traversal removed).
> }
I don't think that will work.
Functions are independent from CFG.
With bpf libraries we will have disjoint functions sitting in the kernel
and check_cfg would need to be done separately from function boundaries.
