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Message-ID: <3ba67d3e220c19c4a921e20f06e26bfe70ae8c80.camel@gmail.com>
Subject: Re: [Bug Report] bpf: incorrectly pruning runtime execution path
From:   Eduard Zingerman <eddyz87@gmail.com>
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     Hao Sun <sunhao.th@gmail.com>, Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        bpf <bpf@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date:   Thu, 14 Dec 2023 01:47:35 +0200
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On Wed, 2023-12-13 at 15:40 -0800, Andrii Nakryiko wrote:
[...]
> >     24: (18) r2 =3D 0x4                     ; R2_w=3D4
> >     26: (7e) if w8 s>=3D w0 goto pc+5
> >     mark_precise: frame0: last_idx 26 first_idx 22 subseq_idx -1
> >     mark_precise: frame0: regs=3Dr5,r8 stack=3D before 24: (18) r2 =3D =
0x4
> >     ...                   ^^^^^^^^^^
> >                           ^^^^^^^^^^
> > Here w8 =3D=3D 15, w0 in range [0, 2], so the jump is being predicted,
> > but for some reason R0 is not among the registers that would be marked =
precise.
>=20
> It is, as a second step. There are two concatenated precision logs:
>=20
> mark_precise: frame0: last_idx 26 first_idx 22 subseq_idx -1
> mark_precise: frame0: regs=3Dr0 stack=3D before 24: (18) r2 =3D 0x4
> mark_precise: frame0: regs=3Dr0 stack=3D before 23: (bf) r5 =3D r8
> mark_precise: frame0: regs=3Dr0 stack=3D before 22: (67) r4 <<=3D 2
>=20
>=20
> The issue is elsewhere, see my last email.

Oh, right, there are two calls to mark_chain_precision in a row, thanks