From: Yonghong Song <yonghong.song@linux.dev>
To: Mahe Tardy <mahe.tardy@gmail.com>, bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
eddyz87@gmail.com, andrii@kernel.org, paul.chaignon@gmail.com
Subject: Re: [PATCH bpf-next] verifier: add prune points to live registers print
Date: Mon, 22 Dec 2025 12:50:29 -0800 [thread overview]
Message-ID: <ac1ac629-9e99-43aa-a16c-a81d5fec9820@linux.dev> (raw)
In-Reply-To: <20251222185813.150505-1-mahe.tardy@gmail.com>
On 12/22/25 10:58 AM, Mahe Tardy wrote:
> Explicitly printing where prune points are placed within the
> instructions allows for better debugging of state pruning issues.
>
> Live regs before insn, prune points (p), and force checkpoints (P):
> 0: .......... (b7) r1 = 0
> 1: .1........ (63) *(u32 *)(r10 -4) = r1
> 2: .......... (bf) r2 = r10
> 3: ..2....... (07) r2 += -4
> 4: ..2....... (18) r1 = 0xffff8cb747b16000
> 6: .12....... (85) call bpf_map_lookup_elem#1
> 7: 0..345.... p (bf) r6 = r0
> 8: ...3456... p (15) if r6 == 0x0 goto pc+6
> 9: ...3456... (b7) r1 = 5
> 10: .1.3456... (b7) r2 = 3
> 11: .123456... p (85) call pc+5
> 12: 0.....6... p (67) r0 <<= 32
> 13: 0.....6... (c7) r0 s>>= 32
> 14: 0.....6... (7b) *(u64 *)(r6 +0) = r0
> 15: .......... p (b7) r0 = 0
> 16: 0......... (95) exit
> 17: .12....... p (bf) r0 = r2
> 18: 01........ (0f) r0 += r1
> 19: 0......... (95) exit
>
> Also uses uppercase P for force checkpoints, which are a subset of prune
> points (a force checkpoint should already be a prune point).
>
> Live regs before insn, prune points (p), and force checkpoints (P):
> 0: .......... p (b7) r1 = 1
> 1: .1........ P (e5) may_goto pc+1
> 2: .......... (05) goto pc-3
> 3: .1........ p (bf) r0 = r1
> 4: 0......... (95) exit
>
> Existing tests on liveness tracking had to be updated with the new
> output format including the prune points.
>
> This proposal patch was presented at Linux Plumbers 2025 in Tokyo along
> the "Making Sense of State Pruning" presentation[^1] with the intent of
> making state pruning more transparent to the user.
>
> [^1]: https://lpc.events/event/19/contributions/2162/
>
> Co-developed-by: Paul Chaignon <paul.chaignon@gmail.com>
> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
> Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
next prev parent reply other threads:[~2025-12-22 20:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-22 18:58 [PATCH bpf-next] verifier: add prune points to live registers print Mahe Tardy
2025-12-22 20:50 ` Yonghong Song [this message]
2025-12-23 6:32 ` Alexei Starovoitov
2025-12-23 10:12 ` Mahe Tardy
2025-12-29 18:48 ` Eduard Zingerman
2025-12-30 0:42 ` Alexei Starovoitov
2025-12-30 1:13 ` Eduard Zingerman
2025-12-30 18:06 ` Alexei Starovoitov
2025-12-30 18:44 ` Eduard Zingerman
2025-12-31 1:11 ` Alexei Starovoitov
2025-12-31 5:47 ` Eduard Zingerman
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