linux-kernel - Re: [PATCH bpf v2 2/2] selftests/bpf: Add socket filter attach test

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Message-ID: <139bf7d77750fdf04d26e1a77c0955466c9a4827.camel@gmail.com>
Date: Mon, 25 Aug 2025 12:32:29 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Puranjay Mohan <puranjay12@...il.com>
Cc: KaFai Wan <kafai.wan@...ux.dev>, puranjay@...nel.org, 
	xukuohai@...weicloud.com, ast@...nel.org, daniel@...earbox.net, 
	john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev,
 song@...nel.org, 	yonghong.song@...ux.dev, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, 	jolsa@...nel.org, mykolal@...com,
 shuah@...nel.org, mrpre@....com, 	linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, 	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf v2 2/2] selftests/bpf: Add socket filter attach test

On Mon, 2025-08-25 at 21:27 +0200, Puranjay Mohan wrote:

[...]

> Hi Eduard,
> 
> You were right, I have verified that the program is hitting the 0xfff
> boundary while doing the call to bpf_skb_load_helper_32
> While jiting this call, emit_a32_mov_i(tmp[1], func, ctx); is called,
> where this issue it triggered.
> 
> The offset in imm_offset() is calculated as:
> ctx->offsets[ctx->prog->len - 1] * 4 + ctx->prologue_bytes +
> ctx->epilogue_bytes + imm_i * 4
> 
> For this program, ctx->offsets[ctx->prog->len - 1] * 4 itself is
> 0x1400 which is above 0xfff boundary.
> So, this is not a bug and expected behaviour with the current
> implementation of the JIT.
> 
> For now, we can merge this and later I will try to improve the JIT so
> it works for bigger programs.

Hi Puranjay,

Thank you for checking this!
What do you think about this test case, do we need it in the suite?

Best regards,
Eduard