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Sat, 12 Sep 2026 11:51:40 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sat, 12 Sep 2026 11:51:39 -0700 Message-Id: Cc: , , , , , , , , , , Subject: Re: [PATCH bpf-next v2 02/13] bpf: compare linked-scalar kinds in regs_exact() From: "Alexei Starovoitov" To: "Vineet Gupta" , , , , , X-Mailer: aerc References: <20260910164635.459558-1-vineet.gupta@linux.dev> <20260910164635.459558-3-vineet.gupta@linux.dev> In-Reply-To: <20260910164635.459558-3-vineet.gupta@linux.dev> On Thu Sep 10, 2026 at 9:46 AM PDT, Vineet Gupta wrote: > regs_exact() memcmp()s up to offsetof(id), so it does not see ->add_const= , > which sits past ->frameno. Compare it explicitly. > > Two cases go from accepted to rejected: > > old {r1.id=3DA, r2.id=3DA+delta} vs cur {r1.id=3DB, r2.id=3DB} > old {r2.id=3DA+delta32} vs cur {r2.id=3DB+delta64} > > The first was rejected before this series -- the kind lived in ->id, so > A+delta was a distinct idmap key -- and the previous patch lost that. The > second was accepted before the series too, which is wrong: alu32 and alu6= 4 > deltas differ in sync_linked_regs(), so the states are not > interchangeable. > > ->delta is inside the memcmp() window and is cleared together with the > kind, so either case needs a kind with delta 0, e.g. "r6 =3D r5; r6 +=3D = 0". > > Only states_equal(..., EXACT) and env->explore_alu_limits reach > regs_exact() for a scalar; regsafe() compares kinds itself on the ordinar= y > path. Neither is easy to drive from a test program, so no selftest. > > Signed-off-by: Vineet Gupta > --- > v2: new. Splits out the comparison RFC 3/6 lost when the kind left > ->id, which was raised on that patch. > > kernel/bpf/states.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/bpf/states.c b/kernel/bpf/states.c > index d974baad37ee..5505d7aaeed0 100644 > --- a/kernel/bpf/states.c > +++ b/kernel/bpf/states.c > @@ -475,6 +475,7 @@ static bool regs_exact(const struct bpf_reg_state *ro= ld, > struct bpf_idmap *idmap) > { > return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) =3D=3D 0 = && > + rold->add_const =3D=3D rcur->add_const && This change should be in the patch 1 otherwise patch 1 is not correct?