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Date: Fri, 25 Sep 2020 21:36:06 -0700 From: John Fastabend <john.fastabend@...il.com> To: Alexei Starovoitov <alexei.starovoitov@...il.com>, 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 Alexei Starovoitov wrote: > 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 +1 > which we will start using soon to send automatic 'applied' emails. Apologies, I updated some scripts and unfortunately typo dropped a '-' and cut off bpf@...r from the CC list. Also I just used it to land two more patches without bpf@...r happy to resend with CC included if folks want. Sorry for the extra work/noise. Thanks.
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