linux-kernel - Re: [PATCH -tip v2 00/10] kprobes: Fix stacktrace with kretprobes

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Message-ID: <20210312185600.2fziqmye77iufrgz@maharaja.localdomain>
Date:   Fri, 12 Mar 2021 10:56:00 -0800
From:   Daniel Xu <dxu@...uu.xyz>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org, kuba@...nel.org,
        mingo@...hat.com, ast@...nel.org, tglx@...utronix.de,
        kernel-team@...com, yhs@...com,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH -tip v2 00/10] kprobes: Fix stacktrace with kretprobes

On Fri, Mar 12, 2021 at 03:41:44PM +0900, Masami Hiramatsu wrote:
> Hello,
> 
> Here is the 2nd version of the series to fix the stacktrace with kretprobe.
> 
> The 1st series is here;
> 
> https://lore.kernel.org/bpf/161495873696.346821.10161501768906432924.stgit@devnote2/
> 
> In this version I merged the ORC unwinder fix for kretprobe which discussed in the
> previous thread. [3/10] is updated according to the Miroslav's comment. [4/10] is
> updated for simplify the code. [5/10]-[9/10] are discussed in the previsous tread
> and are introduced to the series.
> 
> Daniel, can you also test this again? I and Josh discussed a bit different
> method and I've implemented it on this version.

Works great, thanks!

Tested-by: Daniel Xu <dxu@...uu.xyz>

> 
> This actually changes the kretprobe behavisor a bit, now the instraction pointer in
> the pt_regs passed to kretprobe user handler is correctly set the real return
> address. So user handlers can get it via instruction_pointer() API.

While this changes behavior a little bit, I don't think anyone will
mind. I think it's more accurate now.

<...>

Thanks,
Daniel