linux-kernel - Re: [RFC PATCH 7/7] lib/Kconfig.debug: introduce CONFIG_NO_AUTO

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Message-ID: <CAC1kPDNtOAj8qi2mu7ehMLW4KWf+2cSqKt9ahL-fW7J-Fs4f8g@mail.gmail.com>
Date: Tue, 15 Apr 2025 15:13:35 +0800
From: Chen Linxuan <chenlinxuan@...ontech.com>
To: Chen Linxuan <chenlinxuan@...ontech.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Winston Wen <wentao@...ontech.com>, 
	Changbin Du <changbin.du@...il.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [RFC PATCH 7/7] lib/Kconfig.debug: introduce CONFIG_NO_AUTO_INLINE

Chen Linxuan <chenlinxuan@...ontech.com> 于2025年4月11日周五 18:56写道：
>
> From: Winston Wen <wentao@...ontech.com>
>
> Add a new kernel hacking option CONFIG_NO_AUTO_INLINE that prevents the
> compiler from auto-inlining functions not explicitly marked with the
> 'inline' keyword.
>
> This enhancement improves function tracer capabilities as it can only
> trace functions that haven't been inlined by the compiler.
>
> Previous discussions:
> Link: https://lore.kernel.org/all/20181028130945.23581-3-changbin.du@gmail.com/
>
> This patch is modified from 917fad29febd ("kernel hacking: add a config
> option to disable compiler auto-inlining") which can be founded in
> linux-next-history:
> Link: https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next-history.git/commit/?id=917fad29febd
>
> Unlike the original implementation, this patch:
>
> 1. Make it depends on CC_IS_GCC,
>    as Clang 18.1.3 break test_bitmap_const_eval() in lib/test_bitmap.c
>
> 2. Make it depends on X86_64,
>    as I haven't test other architectures

LOONGARCH has been tested, too.

>
> 3. Removes unnecessary cc-option checks per 7d73c3e9c514 ("Makefile:
>    remove stale cc-option checks").
>
> 4. Update help information.
>
> Cc: Changbin Du <changbin.du@...il.com>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Signed-off-by: Winston Wen <wentao@...ontech.com>
> Co-Developed-by: Chen Linxuan <chenlinxuan@...ontech.com>
> Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
> ---
>  Makefile          |  6 ++++++
>  lib/Kconfig.debug | 15 +++++++++++++++
>  2 files changed, 21 insertions(+)
>
> diff --git a/Makefile b/Makefile
> index f42418556507..0a9bf33ce75f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1071,6 +1071,12 @@ endif
>  # Ensure compilers do not transform certain loops into calls to wcslen()
>  KBUILD_CFLAGS += -fno-builtin-wcslen
>
> +ifdef CONFIG_NO_AUTO_INLINE
> +KBUILD_CFLAGS   += -fno-inline-functions \
> +                  -fno-inline-small-functions \
> +                  -fno-inline-functions-called-once
> +endif
> +
>  # change __FILE__ to the relative path to the source directory
>  ifdef building_out_of_srctree
>  KBUILD_CPPFLAGS += $(call cc-option,-ffile-prefix-map=$(srcroot)/=)
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 9fe4d8dfe578..2ebb4802886a 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -436,8 +436,23 @@ config GDB_SCRIPTS
>           instance. See Documentation/process/debugging/gdb-kernel-debugging.rst
>           for further details.
>
> +
>  endif # DEBUG_INFO
>
> +config NO_AUTO_INLINE
> +       bool "Disable compiler auto-inline optimizations (EXPERIMENTAL)"
> +       default n
> +       depends on CC_IS_GCC && (X86 || LOONGARCH)
> +       help
> +         This will prevent the compiler from optimizing the kernel by
> +         auto-inlining functions not marked with the inline keyword.
> +         With this option, only functions explicitly marked with
> +         "inline" will be inlined. This will allow the function tracer
> +         to trace more functions because it only traces functions that
> +         the compiler has not inlined.
> +
> +         If unsure, select N.
> +
>  config FRAME_WARN
>         int "Warn for stack frames larger than"
>         range 0 8192
> --
> 2.48.1
>
>