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Mon, 27 Jul 2026 15:48:30 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v2 10/18] bpf: Fold __szk const size handling into the scalar arg path From: Eduard Zingerman To: Amery Hung , bpf@vger.kernel.org Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, memxor@gmail.com, kernel-team@meta.com Date: Mon, 27 Jul 2026 15:48:27 -0700 In-Reply-To: <20260724190813.1458271-11-ameryhung@gmail.com> References: <20260724190813.1458271-1-ameryhung@gmail.com> <20260724190813.1458271-11-ameryhung@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-07-24 at 12:08 -0700, Amery Hung wrote: > To align helper and kfunc pointer to memory argument handling, move > kfunc constant memorry size argument handling to the kfunc scalar > section. In addition, factor out constant scalar argument handling. >=20 > The constant size argument (__szk) of a kfunc memory/size pair was > recorded into meta->arg_constant by a dedicated block in the > KF_ARG_PTR_TO_MEM_SIZE case, duplicating the "only one constant > argument" and "must be a known constant" checks already in the generic > scalar argument handling. That block also did an explicit i++ to skip > the size argument. >=20 > This also fixes a precision gap: the old dedicated block did not mark > the size register precise, relying on check_mem_size_reg() for that. But > check_mem_size_reg() is skipped when the buffer is a nullable arg passed > as NULL (e.g. bpf_dynptr_slice(_rdwr) with a NULL buffer), so in that > case the __szk value was recorded and used for regs[R0].mem_size without > marking it precise. Routing the size through the scalar path marks it > precise in all cases. Could you please add a test case for this? >=20 > Signed-off-by: Amery Hung > --- Reviewed-by: Eduard Zingerman ...