linux-kernel - Re: [PATCH bpf-next v4 2/4] bpf: Add helper to detect indirect jump targets

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Message-ID: <2e5ed01463ae8f79780a42c4e7f93baeafd2565a.camel@gmail.com>
Date: Wed, 14 Jan 2026 12:46:18 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Xu Kuohai <xukuohai@...weicloud.com>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>,  Andrii Nakryiko <andrii@...nel.org>, Martin KaFai
 Lau <martin.lau@...ux.dev>, Yonghong Song	 <yonghong.song@...ux.dev>,
 Puranjay Mohan <puranjay@...nel.org>, Anton Protopopov
 <a.s.protopopov@...il.com>
Subject: Re: [PATCH bpf-next v4 2/4] bpf: Add helper to detect indirect jump
 targets

On Wed, 2026-01-14 at 17:39 +0800, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@...wei.com>
> 
> Introduce helper bpf_insn_is_indirect_target to determine whether a BPF
> instruction is an indirect jump target. This helper will be used by
> follow-up patches to decide where to emit indirect landing pad instructions.
> 
> Add a new flag to struct bpf_insn_aux_data to mark instructions that are
> indirect jump targets. The BPF verifier sets this flag, and the helper
> checks it to determine whether an instruction is an indirect jump target.
> 
> Since bpf_insn_aux_data is only available before JIT stage, add a new
> field to struct bpf_prog_aux to store a pointer to the bpf_insn_aux_data
> array, making it accessible to the JIT.
> 
> For programs with multiple subprogs, each subprog uses its own private
> copy of insn_aux_data, since subprogs may insert additional instructions
> during JIT and need to update the array. For non-subprog, the verifier's
> insn_aux_data array is used directly to avoid unnecessary copying.
> 
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> ---

Hm, I've missed the fact insn_aux_data is not currently available to jit.
Is it really necessary to copy this array for each subprogram?
Given that we still want to free insn_aux_data after program load,
I'd expect that it should be possible just to pass a pointer with an
offset pointing to a start of specific subprogram. Wdyt?

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