linux-kernel - Re: [PATCH 1/3] ring-buffer: Add uname to match criteria for persistent ring buffer

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Message-ID: <CAHk-=wjThke2-HB_Zi35xHe9ayTPk=zB_kjd0Hr-Yn1oV0ZSsg@mail.gmail.com>
Date: Tue, 17 Dec 2024 10:24:42 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	stable@...r.kernel.org
Subject: Re: [PATCH 1/3] ring-buffer: Add uname to match criteria for
 persistent ring buffer

On Tue, 17 Dec 2024 at 10:19, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> What *woiuld* have been an acceptable model is to actually modify the
> boot-time buffers in place, using actual real heuristics that look at
> whether a pointer was IN THE CODE SECTION OR THE STATIC DATA section
> of the previous boot.
>
> But you never did that. All this delta code has always been complete
> and utter garbage, and complete hacks.

Actually, I think the proper model isn't even that "modify boot time
buffers in place" thing.

The proper model was probably always to just do the "give the raw
data, and analyze the previous boot data in user mode". Don't do
"delta between old and new kernel", print out the actual KASLR base of
the old kernel, and let user mode figure it out. Because user mode may
actually have the old and different vmlinux image too - something that
kernel mode *never* has.

                   Linus