linux-kernel - Re: [PATCH] arm64: Kconfig: Remove selecting replaced HAVE_FUNCTION_GRAPH

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Message-ID: <20250204113614.GD893@willie-the-truck>
Date: Tue, 4 Feb 2025 11:36:15 +0000
From: Will Deacon <will@...nel.org>
To: Lukas Bulwahn <lbulwahn@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-trace-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	linux-arm-kernel@...ts.infradead.org,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lukas Bulwahn <lukas.bulwahn@...hat.com>
Subject: Re: [PATCH] arm64: Kconfig: Remove selecting replaced
 HAVE_FUNCTION_GRAPH_RETVAL

On Fri, Jan 17, 2025 at 07:55:22AM -0500, Lukas Bulwahn wrote:
> From: Lukas Bulwahn <lukas.bulwahn@...hat.com>
> 
> Commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with ftrace_regs")
> replaces the config HAVE_FUNCTION_GRAPH_RETVAL with the config
> HAVE_FUNCTION_GRAPH_FREGS, and it replaces all the select commands in the
> various architecture Kconfig files. In the arm64 architecture, the commit
> adds the 'select HAVE_FUNCTION_GRAPH_FREGS', but misses to remove the
> 'select HAVE_FUNCTION_GRAPH_RETVAL', i.e., the select on the replaced
> config.
> 
> Remove selecting the replaced config. No functional change, just cleanup.
> 
> Fixes: a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with ftrace_regs")
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...hat.com>
> ---
>  arch/arm64/Kconfig | 1 -
>  1 file changed, 1 deletion(-)

Hmm. There are still a couple of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL guards
kicking around:

include/linux/ftrace.h:#ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
kernel/trace/fgraph.c:#ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL

so it's not clear we can just remove the option from arm64 without
breaking ftrace_return_to_handler(). What am I missing?

Will