linux-kernel - Re: [PATCH bpf-next v5 1/3] btf: allow mmap of vmlinux btf

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Message-ID: <CAN+4W8i+PqYDcJjWk+g63W4kdKvhFKSad61q-T=JJky5m7j79w@mail.gmail.com>
Date: Thu, 17 Jul 2025 16:15:07 +0100
From: Lorenz Bauer <lmb@...valent.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Breno Leitao <leitao@...ian.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, Arnd Bergmann <arnd@...db.de>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	linux-arch <linux-arch@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCH bpf-next v5 1/3] btf: allow mmap of vmlinux btf

On Thu, Jul 17, 2025 at 3:49 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:

> __pa_symbol() should work for start_BTF, but would be good
> to double check with Ard that the rest stays linear.

Alexei,

This code in the arm64 setup does make me think we'll be OK.

kernel_code.start   = __pa_symbol(_stext);
kernel_code.end     = __pa_symbol(__init_begin - 1);
kernel_data.start   = __pa_symbol(_sdata);
kernel_data.end     = __pa_symbol(_end - 1);

Using these as start and end only makes sense to me if the addresses
are linear? See
https://elixir.bootlin.com/linux/v6.15.6/source/arch/arm64/kernel/setup.c#L217

Let me know if you want me to double check with Ard regardless.

Best
Lorenz