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Tue, 21 Apr 2026 09:48:46 -0700 (PDT) Message-ID: <3b97c3523aa50ac1b5cab89c817dda3e07e22190.camel@gmail.com> Subject: Re: [PATCH RFC bpf-next 3/4] bpf: replace min/max fields with struct cnum{32,64} From: Eduard Zingerman To: Alexei Starovoitov , bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org Cc: daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, shung-hsi.yu@suse.com, paul.chaignon@gmail.com, harishankar.vishwanathan@gmail.com Date: Tue, 21 Apr 2026 09:48:43 -0700 In-Reply-To: References: <20260421-cnums-everywhere-rfc-v1-v1-0-8f8e98537f48@gmail.com> <20260421-cnums-everywhere-rfc-v1-v1-3-8f8e98537f48@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-04-21 at 09:23 -0700, Alexei Starovoitov wrote: > On Tue Apr 21, 2026 at 3:28 AM PDT, Eduard Zingerman wrote: > > =20 > > static void scalar32_min_max_udiv(struct bpf_reg_state *dst_reg, > > @@ -14119,7 +13548,6 @@ static void scalar32_min_max_udiv(struct bpf_re= g_state *dst_reg, > > reg_u32_max(dst_reg) / src_val); > > =20 > > /* Reset other ranges/tnum to unbounded/unknown. */ > > - reg_set_srange32(dst_reg, S32_MIN, S32_MAX); > > reset_reg64_and_tnum(dst_reg); > > } >=20 > div/mod don't need special cnum_div ? There is an algorithm for that in the paper, but it turned out to be unnecessary for our verification purposes. At-least for the corpora of programs I used for testing. I didn't try the "dumb" multiplication version, expect it to fail for cross sign-domains cases. >=20 > > @@ -15861,38 +15209,54 @@ static void regs_refine_cond_op(struct bpf_re= g_state *reg1, struct bpf_reg_state > > break; > > case BPF_JLE: > > if (is_jmp32) { > > - reg_set_urange32(reg1, reg_u32_min(reg1), min(reg_u32_max(reg1), re= g_u32_max(reg2))); > > - reg_set_urange32(reg2, max(reg_u32_min(reg1), reg_u32_min(reg2)), r= eg_u32_max(reg2)); > > + lo32 =3D cnum32_from_urange(0, reg_u32_max(reg2)); > > + hi32 =3D cnum32_from_urange(reg_u32_min(reg1), U32_MAX); > > + reg1->r32 =3D cnum32_intersect(reg1->r32, lo32); > > + reg2->r32 =3D cnum32_intersect(reg2->r32, hi32); > > } else { > > - reg_set_urange64(reg1, reg_umin(reg1), min(reg_umax(reg1), reg_umax= (reg2))); > > - reg_set_urange64(reg2, max(reg_umin(reg1), reg_umin(reg2)), reg_uma= x(reg2)); > > + lo =3D cnum64_from_urange(0, reg_umax(reg2)); > > + hi =3D cnum64_from_urange(reg_umin(reg1), U64_MAX); > > + reg1->r64 =3D cnum64_intersect(reg1->r64, lo); > > + reg2->r64 =3D cnum64_intersect(reg2->r64, hi); >=20 > Maybe a helper like: > cnum64_intersect_with_range(®1->r64, 0, reg_umax(reg2)); > ? >=20 > Also I found only one case: > dst_reg->r64 =3D cnum64_intersect(u, s); >=20 > all others dst and src are the same. > So maybe: > cnum64_intersect(&dst_reg->r64, ..); > as a main helper and __cnum64_intersect(r->r64, ...) as a subhelper that = returns cnum? Are you concerned about machine code inefficiencies from struct cnum being passed around as a temporary/parameter/return value? Since cnum functions are in a separate compilation unit, I'd guess there won't be much optimization outside LTO builds. Or do you just like the &r->r64 notation more?