linux-kernel - [RFC PATCH kernel] trace: Make FTRACE_MCOUNT_USE

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Date:   Fri, 11 Feb 2022 12:43:13 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     llvm@...ts.linux.dev
Cc:     Alexey Kardashevskiy <aik@...abs.ru>, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: [RFC PATCH kernel] trace: Make FTRACE_MCOUNT_USE_RECORDMCOUNT configurable

For whatever reason LLVM does not allow LTO (Link Time Optimization) if
FTRACE_MCOUNT_USE_RECORDMCOUNT is enabled.

This allows disabling just this option instead of disabling all FTRACE
options.

Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
---

Or disabling FTRACE is the right thing to do if HAS_LTO_CLANG=y?

Came from arch/Kconfig:

config HAS_LTO_CLANG
        def_bool y
        depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
        depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
        depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
        depends on ARCH_SUPPORTS_LTO_CLANG
        depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT  <======
        depends on !KASAN || KASAN_HW_TAGS
        depends on !GCOV_KERNEL


---
 kernel/trace/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a5eb5e7fd624..87d82d2b0b0b 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -704,7 +704,8 @@ config FTRACE_MCOUNT_USE_OBJTOOL
 	depends on FTRACE_MCOUNT_RECORD
 
 config FTRACE_MCOUNT_USE_RECORDMCOUNT
-	def_bool y
+	bool "Enable FTRACE_MCOUNT_USE_RECORDMCOUNT"
+	default y
 	depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
 	depends on !FTRACE_MCOUNT_USE_CC
 	depends on !FTRACE_MCOUNT_USE_OBJTOOL
-- 
2.30.2