linux-kernel - Re: [PATCH v2] ftrace: Add FTRACE_MCOUNT_MAX

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Date:   Fri, 27 May 2022 12:04:14 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [PATCH v2] ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding
 weak function


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 26 May 2022 04:50:17 +0200
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> 
> > > The real fix would be to fix kallsyms to not show address of weak
> > > functions as the function before it. But that would require adding code in
> > > the build to add function size to kallsyms so that it can know when the
> > > function ends instead of just using the start of the next known symbol.  
> > 
> > Yeah, so I actually have a (prototype...) objtool based kallsyms 
> > implementation in the (way too large) fast-headers tree that is both faster 
> > & allows such details in principle:
> 
> Nice.
> 
> Will this work for other architectures too?

For those which implement objtool, it certainly should: as we parse through 
each object file during the build, generating kallsyms data structures is 
relatively straightforward.

Objtool availability is a big gating condition though. :-/

[ ... and still Acked-by on -v4 too. ]

Thanks,

	Ingo