linux-kernel - Re: [RFC] ftrace: Add support to keep some functions out of ftrace

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Message-ID: <20220814073215.0a030a45@rorschach.local.home>
Date:   Sun, 14 Aug 2022 07:32:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, 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>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace

On Sat, 13 Aug 2022 15:02:52 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Index: linux-trace.git/scripts/Makefile.lib
> ===================================================================
> --- linux-trace.git.orig/scripts/Makefile.lib
> +++ linux-trace.git/scripts/Makefile.lib
> @@ -233,7 +233,8 @@ objtool_args =								\
>  	$(if $(CONFIG_HAVE_JUMP_LABEL_HACK), --hacks=jump_label)	\
>  	$(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr)		\
>  	$(if $(CONFIG_X86_KERNEL_IBT), --ibt)				\
> -	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
> +	$(if $(filter $(shell basename $@),$(NO_MCOUNT_FILES)),,	\
> +		$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount))	\

I believe there's some security and other validations that objtool does
that requires it to know about the mcount locations.

If BPF is doing something unique, and modifying code as well (outside
the jump label and ftrace work), does objtool need to know about that too?

-- Steve


>  	$(if $(CONFIG_UNWINDER_ORC), --orc)				\
>  	$(if $(CONFIG_RETPOLINE), --retpoline)				\
>  	$(if $(CONFIG_SLS), --sls)					\