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Message-ID: <20220211214722.4373ca83@rorschach.local.home>
Date: Fri, 11 Feb 2022 21:47:22 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexey Kardashevskiy <aik@...abs.ru>
Cc: llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nathan Chancellor <nathan@...nel.org>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC PATCH kernel] trace: Make FTRACE_MCOUNT_USE_RECORDMCOUNT
configurable
On Fri, 11 Feb 2022 12:43:13 +1100
Alexey Kardashevskiy <aik@...abs.ru> wrote:
> 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.
What FTRACE options are you talking about?
>
> 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
I don't think this does what you think it does.
This is not something that should be user selectable. What exactly are
you trying to accomplish here?
-- Steve
> depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
> depends on !FTRACE_MCOUNT_USE_CC
> depends on !FTRACE_MCOUNT_USE_OBJTOOL
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