linux-kernel - Re: [RFC PATCH 24/32] x86/ftrace: Enable HAVE_FUNCTION_GRAPH

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20231105183301.38be5598@rorschach.local.home>
Date:   Sun, 5 Nov 2023 18:33:01 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Florent Revest <revest@...omium.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alan Maguire <alan.maguire@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Guo Ren <guoren@...nel.org>
Subject: Re: [RFC PATCH 24/32] x86/ftrace: Enable HAVE_FUNCTION_GRAPH_FREGS

On Mon, 6 Nov 2023 00:17:34 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> Changelog nor code made it clear this was partial anything. So this is
> still the partial thing?
> 
> Can we then pretty clear clarify all that, and make it clear which regs
> are in there? Because when I do 'vim -t ftrace_regs' it just gets me a
> seemingly pointless wrapper struct, no elucidating comments nothingses.

I agree it should be better documented (like everything else). The
ftrace_regs must have all the registers needed to produce a function's
arguments. For x86_64, that would be:

  rdi, rsi, rdx, r8, r9, rsp

Basically anything that is needed to call mcount/fentry.

But yes, it's still partial registers but for archs that support
FTRACE_WITH_REGS, it can also hold all pt_regs which can be retrieved
by the arch_ftrace_get_regs(), which is why there's a pt_regs struct in
the x86 version. But that's not the case for arm64, as
arch_ftrace_get_regs() will always return NULL.

> 
> > You even Acked the patch:
> >
> > commit 02a474ca266a47ea8f4d5a11f4ffa120f83730ad
> > Author: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > Date:   Tue Oct 27 10:55:55 2020 -0400  
> 
> You expect me to remember things from 3 years ago?

Heh, of course not. I just thought it amusing that I created
ftrace_regs because of you and then 3 years later you ask to get rid of
it. But the real issue is that it's not documented clearly why it
exists, and that should be rectified.

Thanks,

-- Steve