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Date: Fri, 25 Sep 2020 16:56:10 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: John Fastabend <john.fastabend@...il.com> Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org> Subject: Re: [bpf-next PATCH 1/2] bpf, verifier: Remove redundant var_off.value ops in scalar known reg cases On Thu, Sep 24, 2020 at 11:45 AM John Fastabend <john.fastabend@...il.com> wrote: > > In BPF_AND and BPF_OR alu cases we have this pattern when the src and dst > tnum is a constant. > > 1 dst_reg->var_off = tnum_[op](dst_reg->var_off, src_reg.var_off) > 2 scalar32_min_max_[op] > 3 if (known) return > 4 scalar_min_max_[op] > 5 if (known) > 6 __mark_reg_known(dst_reg, > dst_reg->var_off.value [op] src_reg.var_off.value) > > The result is in 1 we calculate the var_off value and store it in the > dst_reg. Then in 6 we duplicate this logic doing the op again on the > value. > > The duplication comes from the the tnum_[op] handlers because they have > already done the value calcuation. For example this is tnum_and(). > > struct tnum tnum_and(struct tnum a, struct tnum b) > { > u64 alpha, beta, v; > > alpha = a.value | a.mask; > beta = b.value | b.mask; > v = a.value & b.value; > return TNUM(v, alpha & beta & ~v); > } > > So lets remove the redundant op calculation. Its confusing for readers > and unnecessary. Its also not harmful because those ops have the > property, r1 & r1 = r1 and r1 | r1 = r1. > > Signed-off-by: John Fastabend <john.fastabend@...il.com> Applied. Thanks for the follow up. In the future please always cc bpf@...r for two reasons: - to get proper 'Link:' integrated in git commit - to get them into a new instance of https://patchwork.kernel.org/project/bpf/list which we will start using soon to send automatic 'applied' emails.
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