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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id a11-20020a056512020b00b0050eae170e04sm127175lfo.81.2024.01.08.16.52.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jan 2024 16:52:11 -0800 (PST) Message-ID: <30a5c5b913af04d645f1b8d504892704e6be920b.camel@gmail.com> Subject: Re: [PATCH bpf-next 1/3] bpf: simplify try_match_pkt_pointers() From: Eduard Zingerman To: Andrii Nakryiko Cc: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, zenczykowski@gmail.com Date: Tue, 09 Jan 2024 02:52:10 +0200 In-Reply-To: References: <20240108132802.6103-1-eddyz87@gmail.com> <20240108132802.6103-2-eddyz87@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.2 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-01-08 at 16:40 -0800, Andrii Nakryiko wrote: [...] > > @@ -14684,90 +14687,31 @@ static bool try_match_pkt_pointers(const stru= ct bpf_insn *insn, > > if (BPF_CLASS(insn->code) =3D=3D BPF_JMP32) > > return false; > >=20 > > - switch (BPF_OP(insn->code)) { > > + if (dst_reg->type =3D=3D PTR_TO_PACKET_END || > > + src_reg->type =3D=3D PTR_TO_PACKET_META) { > > + swap(src_reg, dst_reg); > > + dst_regno =3D insn->src_reg; > > + opcode =3D flip_opcode(opcode); > > + } > > + > > + if ((dst_reg->type !=3D PTR_TO_PACKET || > > + src_reg->type !=3D PTR_TO_PACKET_END) && > > + (dst_reg->type !=3D PTR_TO_PACKET_META || > > + !reg_is_init_pkt_pointer(src_reg, PTR_TO_PACKET))) > > + return false; >=20 > this inverted original condition just breaks my brain, I can't wrap my > head around it :) I think the original is easier to reason about > because it's two clear allowable patterns for which we do something. I > understand that this early exit reduces nestedness, but at least for > me it would be simpler to have the original non-inverted condition > with a nested switch. I'm not sure I understand what you mean by nested switch. If I write it down like below, would that be more clear? bool pkt_data_vs_pkt_end; bool pkt_meta_vs_pkt_data; ... pkt_data_vs_pkt_end =3D dst_reg->type =3D=3D PTR_TO_PACKET && src_reg->type =3D=3D PTR_TO_PAC= KET_END; pkt_meta_vs_pkt_data =3D dst_reg->type =3D=3D PTR_TO_PACKET_META && reg_is_init_pkt_pointer(sr= c_reg, PTR_TO_PACKET); if (!pkt_data_vs_pkt_end && !pkt_meta_vs_pkt_data) return false; > > + > > + switch (opcode) { > > case BPF_JGT: > > - if ((dst_reg->type =3D=3D PTR_TO_PACKET && > > - src_reg->type =3D=3D PTR_TO_PACKET_END) || > > - (dst_reg->type =3D=3D PTR_TO_PACKET_META && > > - reg_is_init_pkt_pointer(src_reg, PTR_TO_PACKET))) = { > > - /* pkt_data' > pkt_end, pkt_meta' > pkt_data */ > > - find_good_pkt_pointers(this_branch, dst_reg, > > - dst_reg->type, false); > > - mark_pkt_end(other_branch, insn->dst_reg, true)= ; > it seems like you can make a bit of simplification if mark_pkt_end > would just accept struct bpf_reg_state * instead of int regn (you > won't need to keep track of dst_regno at all, right?) mark_pkt_end() changes the register from either this_branch or other_branch= . I can introduce local pointers dst_this/dst_other and swap those, but I'm not sure it's worth it. [...]