linux-kernel - Re: [PATCH v14 04/19] function_graph: Replace fgraph_ret_regs with ftrace

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Message-ID: <20240917095538.GA27384@willie-the-truck>
Date: Tue, 17 Sep 2024 10:55:39 +0100
From: Will Deacon <will@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Florent Revest <revest@...omium.org>,
	linux-trace-kernel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v14 04/19] function_graph: Replace fgraph_ret_regs with
 ftrace_regs

On Sun, Sep 15, 2024 at 05:11:44AM -0400, Steven Rostedt wrote:
> On Fri, 13 Sep 2024 00:08:51 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Use ftrace_regs instead of fgraph_ret_regs for tracing return value
> > on function_graph tracer because of simplifying the callback interface.
> > 
> > The CONFIG_HAVE_FUNCTION_GRAPH_RETVAL is also replaced by
> > CONFIG_HAVE_FUNCTION_GRAPH_FREGS.
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > ---
> >  Changes in v8:
> >   - Newly added.
> > ---
> >  arch/arm64/Kconfig                  |    1 +
> >  arch/arm64/include/asm/ftrace.h     |   23 ++++++-----------------
> >  arch/arm64/kernel/asm-offsets.c     |   12 ------------
> >  arch/arm64/kernel/entry-ftrace.S    |   32 ++++++++++++++++++--------------

The arm64 part looks good to me, although passing a partially-populated
struct out of asm feels like it's going to cause us hard-to-debug
problems down the line if any of those extra fields get used. How hard
would it be to poison the unpopulated members of 'ftrace_regs'?

Will