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

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Message-ID: <06952937f3dd04e7f68bbd288da23f00ae83c213.camel@linux.dev>
Date: Sat, 16 Aug 2025 23:14:54 +0800
From: KaFai Wan <kafai.wan@...ux.dev>
To: Eduard Zingerman <eddyz87@...il.com>, Puranjay Mohan
 <puranjay12@...il.com>
Cc: 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 Thu, 2025-08-14 at 09:06 -0700, Eduard Zingerman wrote:
> On Thu, 2025-08-14 at 13:23 +0200, Puranjay Mohan wrote:
> > On Thu, Aug 14, 2025 at 2:35 AM Eduard Zingerman
> > <eddyz87@...il.com> wrote:
> > > 
> > > On Wed, 2025-08-13 at 23:29 +0800, KaFai Wan wrote:
> > > > This test verifies socket filter attachment functionality on
> > > > architectures
> > > > supporting either BPF JIT compilation or the interpreter.
> > > > 
> > > > It specifically validates the fallback to interpreter behavior
> > > > when JIT fails,
> > > > particularly targeting ARMv6 devices with the following
> > > > configuration:
> > > >   # CONFIG_BPF_JIT_ALWAYS_ON is not set
> > > >   CONFIG_BPF_JIT_DEFAULT_ON=y
> > > > 
> > > > Signed-off-by: KaFai Wan <kafai.wan@...ux.dev>
> > > > ---
> > > 
> > > This test should not be landed as-is, first let's do an analysis
> > > for
> > > why the program fails to jit compile on arm.
> > > 
> > > I modified kernel to dump BPF program before jit attempt, but
> > > don't
> > > see anything obviously wrong with it.  The patch to get
> > > disassembly
> > > and disassembly itself with resolved kallsyms are attached.
> > > 
> > > Can someone with access to ARM vm/machine take a looks at this?
> > > Puranjay, Xu, would you have some time?
> > 
> > Hi Eduard,
> > Thanks for the email, I will look into it.
> > 
> > Let me try to boot a kernel on ARMv6 qemu and reproduce this.
> 
> Thank you, Puranjay,
> 
> While looking at the code yesterday I found a legit case for failing
> to jit on armv6:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/arch/arm/net/bpf_jit_32.c#n445
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/arch/arm/net/bpf_jit_32.c#n2089
> 
> But attached program does not seem to be that big to hit 0xfff
> boundary.

Hi Eduard, Puranjay

OpenWRT users reported several tests that aren't working properly,
which may be helpful.

https://github.com/openwrt/openwrt/issues/19405#issuecomment-3121390534
https://github.com/openwrt/openwrt/issues/19405#issuecomment-3176820629

-- 
Thanks,
KaFai