linux-kernel - Re: [PATCH V4 03/13] kprobes: Add symbols for kprobe insn pages

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Message-ID: <20200324123108.GO20696@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Mar 2020 13:31:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 03/13] kprobes: Add symbols for kprobe insn pages

On Wed, Mar 04, 2020 at 11:06:23AM +0200, Adrian Hunter wrote:
> Symbols are needed for tools to describe instruction addresses. Pages
> allocated for kprobe's purposes need symbols to be created for them.
> Add such symbols to be visible via /proc/kallsyms.
> 
> Note: kprobe insn pages are not used if ftrace is configured. To see the
> effect of this patch, the kernel must be configured with:
> 
> 	# CONFIG_FUNCTION_TRACER is not set
> 	CONFIG_KPROBES=y
> 
> and for optimised kprobes:
> 
> 	CONFIG_OPTPROBES=y
> 
> Example on x86:
> 
> 	# perf probe __schedule
> 	Added new event:
> 	  probe:__schedule     (on __schedule)
> 	# cat /proc/kallsyms | grep '\[__builtin__kprobes\]'
> 	ffffffffc00d4000 t kprobe_insn_page     [__builtin__kprobes]
> 	ffffffffc00d6000 t kprobe_optinsn_page  [__builtin__kprobes]
> 

I'm confused; why are you iterating pages and not slots? A 'page' is not
a symbol, they contain text, sometimes.

If you iterate slots you can even get them a proper name; something
like:

	optinsn-sym+xxx [__builtin__kprobes]

	insn-sym+xxx [__builtin__kprobes]