From: Shung-Hsi Yu <shung-hsi.yu@suse.com>
To: Andrii Nakryiko <andrii@kernel.org>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
martin.lau@kernel.org, kernel-team@meta.com
Subject: Re: [PATCH v4 bpf-next 1/7] bpf: improve JEQ/JNE branch taken logic
Date: Mon, 23 Oct 2023 10:33:59 +0800 [thread overview]
Message-ID: <ZTXbl7MsUlXgg9d1@u94a> (raw)
In-Reply-To: <20231022205743.72352-2-andrii@kernel.org>
On Sun, Oct 22, 2023 at 01:57:37PM -0700, Andrii Nakryiko wrote:
> When determining if if/else branch will always or never be taken, use
Nitpick: "... if an if/else branch will ..."
^^
> signed range knowledge in addition to currently used unsigned range knowledge.
> If either signed or unsigned range suggests that condition is
> always/never taken, return corresponding branch_taken verdict.
>
> Current use of unsigned range for this seems arbitrary and unnecessarily
> incomplete. It is possible for *signed* operations to be performed on
> register, which could "invalidate" unsigned range for that register. In
> such case branch_taken will be artificially useless, even if we can
> still tell that some constant is outside of register value range based
> on its signed bounds.
>
> veristat-based validation shows zero differences across selftests,
> Cilium, and Meta-internal BPF object files.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Otherwise,
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
next prev parent reply other threads:[~2023-10-23 2:34 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-22 20:57 [PATCH v4 bpf-next 0/7] BPF register bounds logic and testing improvements Andrii Nakryiko
2023-10-22 20:57 ` [PATCH v4 bpf-next 1/7] bpf: improve JEQ/JNE branch taken logic Andrii Nakryiko
2023-10-23 2:33 ` Shung-Hsi Yu [this message]
2023-10-22 20:57 ` [PATCH v4 bpf-next 2/7] bpf: derive smin/smax from umin/max bounds Andrii Nakryiko
2023-10-23 2:36 ` Shung-Hsi Yu
2023-10-24 13:08 ` Daniel Borkmann
2023-10-24 14:53 ` Andrii Nakryiko
2023-10-24 15:43 ` Daniel Borkmann
2023-10-22 20:57 ` [PATCH v4 bpf-next 3/7] bpf: enhance subregister bounds deduction logic Andrii Nakryiko
2023-10-23 3:20 ` Shung-Hsi Yu
2023-10-23 3:56 ` Shung-Hsi Yu
2023-10-23 16:23 ` Andrii Nakryiko
2023-10-24 12:05 ` Shung-Hsi Yu
2023-10-24 12:22 ` Shung-Hsi Yu
2023-10-24 15:31 ` Alexei Starovoitov
2023-10-27 8:16 ` Shung-Hsi Yu
2023-10-22 20:57 ` [PATCH v4 bpf-next 4/7] bpf: improve deduction of 64-bit bounds from 32-bit bounds Andrii Nakryiko
2023-10-22 20:57 ` [PATCH v4 bpf-next 5/7] bpf: try harder to deduce register bounds from different numeric domains Andrii Nakryiko
2023-10-22 20:57 ` [PATCH v4 bpf-next 6/7] bpf: drop knowledge-losing __reg_combine_{32,64}_into_{64,32} logic Andrii Nakryiko
2023-10-22 20:57 ` [PATCH v4 bpf-next 7/7] selftests/bpf: BPF register range bounds tester Andrii Nakryiko
2023-10-22 23:01 ` kernel test robot
2023-10-24 13:40 ` [PATCH v4 bpf-next 0/7] BPF register bounds logic and testing improvements patchwork-bot+netdevbpf
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