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Message-ID: <YbOANJLMlllo6B7e@archlinux-ax161>
Date: Fri, 10 Dec 2021 09:28:36 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>,
Masahiro Yamada <masahiroy@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Kconfig.debug: Make DEBUG_INFO selectable from a choice
On Thu, Dec 09, 2021 at 04:09:10PM -0800, Kees Cook wrote:
> Currently it's not possible to enable DEBUG_INFO for an all*config
> build, since it is marked as "depends on !COMPILE_TEST". This generally
> makes sense because a debug build of an all*config target ends up taking
> much longer and the output is much larger. Having this be "default off"
> makes sense. However, there are cases where enabling DEBUG_INFO for such
> builds is useful for doing treewide A/B comparisons of build options,
> etc.
>
> Make DEBUG_INFO selectable from any of the DWARF version choice options,
> with DEBUG_INFO_NONE being the default for COMPILE_TEST. The mutually
> exclusive relationship between DWARF5 and BTF must be inverted, but the
> result remains the same. Additionally moves DEBUG_KERNEL and DEBUG_MISC
> up to the top of the menu because was enabling features _above_ it,
> making it weird to navigate menuconfig.
>
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> ---
> lib/Kconfig.debug | 142 +++++++++++++++++++++++++---------------------
> 1 file changed, 76 insertions(+), 66 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5c12bde10996..70ef47e92681 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -208,20 +208,89 @@ config DEBUG_BUGVERBOSE
>
> endmenu # "printk and dmesg options"
>
> +config DEBUG_KERNEL
> + bool "Kernel debugging"
> + help
> + Say Y here if you are developing drivers or trying to debug and
> + identify kernel problems.
> +
> +config DEBUG_MISC
> + bool "Miscellaneous debug code"
> + default DEBUG_KERNEL
> + depends on DEBUG_KERNEL
> + help
> + Say Y here if you need to enable miscellaneous debug code that should
> + be under a more specific debug option but isn't.
> +
> menu "Compile-time checks and compiler options"
>
> config DEBUG_INFO
> - bool "Compile the kernel with debug info"
> - depends on DEBUG_KERNEL && !COMPILE_TEST
> + bool
> help
> - If you say Y here the resulting kernel image will include
> - debugging info resulting in a larger kernel image.
> + A kernel debug info option other than "None" has been selected
> + in the "Debug information" choice below, indicating that debug
> + information will be generated for build targets.
> +
> +choice
> + prompt "Debug information"
> + depends on DEBUG_KERNEL
> + default DEBUG_INFO_NONE if COMPILE_TEST
> + default DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT if DEBUG_KERNEL
> + help
> + Selecting something other than "None" results in a kernel image
> + that will include debugging info resulting in a larger kernel image.
> This adds debug symbols to the kernel and modules (gcc -g), and
> is needed if you intend to use kernel crashdump or binary object
> tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> - Say Y here only if you plan to debug the kernel.
>
> - If unsure, say N.
> + Choose which version of DWARF debug info to emit. If unsure,
> + select "Toolchain default".
> +
> +config DEBUG_INFO_NONE
> + bool "Disable debug information"
> + help
> + Do not build the kernel with debugging information, which will
> + result in a faster and smaller build.
> +
> +config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> + bool "Rely on the toolchain's implicit default DWARF version"
> + select DEBUG_INFO
> + help
> + The implicit default version of DWARF debug info produced by a
> + toolchain changes over time.
> +
> + This can break consumers of the debug info that haven't upgraded to
> + support newer revisions, and prevent testing newer versions, but
> + those should be less common scenarios.
> +
> +config DEBUG_INFO_DWARF4
> + bool "Generate DWARF Version 4 debuginfo"
> + select DEBUG_INFO
> + help
> + Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
> +
> + If you have consumers of DWARF debug info that are not ready for
> + newer revisions of DWARF, you may wish to choose this or have your
> + config select this.
> +
> +config DEBUG_INFO_DWARF5
> + bool "Generate DWARF Version 5 debuginfo"
> + select DEBUG_INFO
> + depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
> + help
> + Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc
> + 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
> + draft features until 7.0), and gdb 8.0+.
> +
> + Changes to the structure of debug info in Version 5 allow for around
> + 15-18% savings in resulting image and debug info section sizes as
> + compared to DWARF Version 4. DWARF Version 5 standardizes previous
> + extensions such as accelerators for symbol indexing and the format
> + for fission (.dwo/.dwp) files. Users may not want to select this
> + config if they rely on tooling that has not yet been updated to
> + support DWARF Version 5.
> +
> +endchoice # "Debug information"
>
> if DEBUG_INFO
>
> @@ -267,55 +336,11 @@ config DEBUG_INFO_SPLIT
> to know about the .dwo files and include them.
> Incompatible with older versions of ccache.
>
> -choice
> - prompt "DWARF version"
> - help
> - Which version of DWARF debug info to emit.
> -
> -config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> - bool "Rely on the toolchain's implicit default DWARF version"
> - help
> - The implicit default version of DWARF debug info produced by a
> - toolchain changes over time.
> -
> - This can break consumers of the debug info that haven't upgraded to
> - support newer revisions, and prevent testing newer versions, but
> - those should be less common scenarios.
> -
> - If unsure, say Y.
> -
> -config DEBUG_INFO_DWARF4
> - bool "Generate DWARF Version 4 debuginfo"
> - help
> - Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
> -
> - If you have consumers of DWARF debug info that are not ready for
> - newer revisions of DWARF, you may wish to choose this or have your
> - config select this.
> -
> -config DEBUG_INFO_DWARF5
> - bool "Generate DWARF Version 5 debuginfo"
> - depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
> - depends on !DEBUG_INFO_BTF
> - help
> - Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc
> - 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
> - draft features until 7.0), and gdb 8.0+.
> -
> - Changes to the structure of debug info in Version 5 allow for around
> - 15-18% savings in resulting image and debug info section sizes as
> - compared to DWARF Version 4. DWARF Version 5 standardizes previous
> - extensions such as accelerators for symbol indexing and the format
> - for fission (.dwo/.dwp) files. Users may not want to select this
> - config if they rely on tooling that has not yet been updated to
> - support DWARF Version 5.
> -
> -endchoice # "DWARF version"
> -
> config DEBUG_INFO_BTF
> bool "Generate BTF typeinfo"
> depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
> depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
> + depends on !DEBUG_INFO_DWARF5
> help
> Generate deduplicated BTF type information from DWARF debug info.
> Turning this on expects presence of pahole tool, which will convert
> @@ -584,21 +609,6 @@ source "lib/Kconfig.kcsan"
>
> endmenu
>
> -config DEBUG_KERNEL
> - bool "Kernel debugging"
> - help
> - Say Y here if you are developing drivers or trying to debug and
> - identify kernel problems.
> -
> -config DEBUG_MISC
> - bool "Miscellaneous debug code"
> - default DEBUG_KERNEL
> - depends on DEBUG_KERNEL
> - help
> - Say Y here if you need to enable miscellaneous debug code that should
> - be under a more specific debug option but isn't.
> -
> -
> menu "Memory Debugging"
>
> source "mm/Kconfig.debug"
> --
> 2.30.2
>
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