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Message-ID: <d1918863-4312-d40d-c22b-d8ce05f65df8@netronome.com>
Date: Tue, 10 Apr 2018 13:54:18 +0100
From: Jiong Wang <jiong.wang@...ronome.com>
To: Edward Cree <ecree@...arflare.com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Daniel Borkmann <daniel@...earbox.net>
Cc: netdev@...r.kernel.org
Subject: Re: [RFC PATCH v3 bpf-next 0/5] bpf/verifier: subprog/func_call
simplifications
On 06/04/2018 18:11, Edward Cree wrote:
> By storing subprog boundaries as a subprogno mark on each insn, rather than
> a start (and implicit end) for each subprog, the code handling subprogs can
> in various places be made simpler, more explicit, and more efficient (i.e.
> better asymptotic complexity).
IMHO, the subprog number might be much smaller than insn number, so just
keeping sorted subprog information in env->subprog_info and do bsearch
looks reasonable to me.
While the new added "subprogno" field is only used round find_subprog, so
I feel it is a little bit heavy to allocate a delicated field that wouldn't
be used broadly for each instruction.
> This also lays the ground for possible
> future work in which an extension of the check_subprogs() code to cover
> basic blocks could replace check_cfg(), which currently largely duplicates
> the insn-walking part.
I was thinking to remove the insn-walk duplication in the other way by
center them in the DFS insn-walk in check_cfg, as we can't remove that one
before we migrate to other loop detection method. This approach is
questionable though.
> Some other changes were also included to support this:
> * Per-subprog info is stored in env->subprog_info, an array of structs,
> rather than several arrays with a common index.
> * Subprog numbers and corresponding subprog_info index are now 0-based;
> subprog 0 is the main()-function of the program, starting at insn 0.
> * Call graph is now stored in the new bpf_subprog_info struct; used here
> for check_max_stack_depth() but may have other uses too.
Ack above changes which center all subprog related info into
env->subprog_info and the new addition of callee field.
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