linux-kernel - [PATCH bpf-next v2 1/4] ftrace: Allow users to disable ftrace direct call

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Date:   Tue, 13 Sep 2022 12:27:29 -0400
From:   Xu Kuohai <xukuohai@...weicloud.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Florent Revest <revest@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Marc Zyngier <maz@...nel.org>, Guo Ren <guoren@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH bpf-next v2 1/4] ftrace: Allow users to disable ftrace direct call

From: Xu Kuohai <xukuohai@...wei.com>

To support ftrace direct call on arm64, multiple NOP instructions need
to be added to the ftrace fentry, which will make the kernel image
larger. For users who don't need direct calls, they should not pay this
unnecessary price, so they should be allowed to disable this option.

Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
---
 kernel/trace/Kconfig | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1052126bdca2..fc8a22f1a6a0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -240,9 +240,14 @@ config DYNAMIC_FTRACE_WITH_REGS
 	depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
 
 config DYNAMIC_FTRACE_WITH_DIRECT_CALLS
-	def_bool y
+	bool "Support for calling custom trampoline from fentry directly"
+	default y
 	depends on DYNAMIC_FTRACE_WITH_REGS
 	depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+	help
+	  This option enables calling custom trampoline from ftrace fentry
+	  directly, instead of using ftrace regs caller. This may reserve more
+	  space in the fentry, making the kernel image larger.
 
 config DYNAMIC_FTRACE_WITH_ARGS
 	def_bool y
-- 
2.30.2