Kconfig.debug: make DEBUG_INFO selectable from a choice

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 they were
enabling features _above_ it, making it weird to navigate menuconfig.

[keescook@chromium.org: make DEBUG_INFO always default=n]
  Link: https://lkml.kernel.org/r/20220128214131.580131-1-keescook@chromium.org
  Link: https://lore.kernel.org/lkml/YfRY6+CaQxX7O8vF@dev-arch.archlinux-ax161

Link: https://lkml.kernel.org/r/20220125075126.891825-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -208,20 +208,87 @@ 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"
+	bool
-	depends on DEBUG_KERNEL && !COMPILE_TEST
 	help
-	  If you say Y here the resulting kernel image will include
+	  A kernel debug info option other than "None" has been selected
-	  debugging info resulting in a larger kernel image.
+	  in the "Debug information" choice below, indicating that debug
+	  information will be generated for build targets.
+
+choice
+	prompt "Debug information"
+	depends on 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
 
@@ -267,56 +334,12 @@ 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 BPF_SYSCALL
+	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
@@ -585,20 +608,6 @@ 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 "Networking Debugging"
 
 source "net/Kconfig.debug"