linux-kernel - [PATCH v3 1/4] DYNAMIC_FTRACE configurable with and without REGS

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Message-Id: <20181001141643.331EE68BC7@newverein.lst.de>
Date:   Mon,  1 Oct 2018 16:16:43 +0200 (CEST)
From:   duwe@....de (Torsten Duwe)
To:     Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Julien Thierry <julien.thierry@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: [PATCH v3 1/4] DYNAMIC_FTRACE configurable with and without REGS

In commit 06aeaaeabf69da4, many ftrace-related config options are
consolidated. By accident, I guess, the choice about DYNAMIC_FTRACE
and DYNAMIC_FTRACE_WITH_REGS is no longer available explicitly but
determined by the sole availability on the architecture.

This makes it hard to introduce DYNAMIC_FTRACE_WITH_REGS if it depends
on new compiler features or other new properties of the toolchain
without breaking existing configurations.

This patch turns the def_bool into an actual choice. Should the toolchain
not meet the requirements for _WITH_REGS it can be turned off.

Signed-off-by: Torsten Duwe <duwe@...e.de>


--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -508,9 +508,15 @@ config DYNAMIC_FTRACE
 	  otherwise has native performance as long as no tracing is active.
 
 config DYNAMIC_FTRACE_WITH_REGS
-	def_bool y
+	bool "Include register content tracking in dynamic ftrace facility"
+	default y
 	depends on DYNAMIC_FTRACE
 	depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
+	help
+	  This architecture supports the inspection of register contents,
+	  as passed between functions, at the dynamic ftrace points.
+	  This is also a prerequisite for Kernel Live Patching (KLP).
+	  When in doubt, say Y.
 
 config FUNCTION_PROFILER
 	bool "Kernel function profiler"