linux-kernel - [PATCH v3] kbuild: add debug level and macro defs options

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Date:   Mon, 15 Aug 2022 04:33:17 +0300
From:   Dmitrii Bundin <dmitrii.bundin.a@...il.com>
To:     masahiroy@...nel.org
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        edumazet@...gle.com, isabbasso@...eup.net, jpoimboe@...nel.org,
        keescook@...omium.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...musvillemoes.dk,
        dmitrii.bundin.a@...il.com, maskray@...gle.com,
        michal.lkml@...kovi.net, nathan@...nel.org,
        ndesaulniers@...gle.com, peterz@...radead.org, vbabka@...e.cz
Subject: [PATCH v3] kbuild: add debug level and macro defs options

Adds config options to control debug info level and producing of macro
definitions for GCC/Clang.

Option DEBUG_INFO_LEVEL is responsible for controlling debug info level.
Before GCC 11 and Clang 12 -gsplit-dwarf implicitly uses -g2. To provide
a way to override the setting with, e.g. -g1, DEBUG_INFO_LEVEL is set
independently from DEBUG_INFO_SPLIT.

Option DEBUG_MACRO_DEFINITIONS is responsible for controlling inclusion
of macro definitions. Since Clang uses -fdebug-macro to control if macro
definitions are produced which is different from GCC, provides a
compiler-specific way of handling macro inclusion. The option is handled
after DEBUG_INFO_LEVEL since -g3 -g2 implies -g2, but -g2 -g3 implies
-g3 and GCC uses -g3 to produce macro definitions.

Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@...il.com>
---

Changes in v2: https://lore.kernel.org/all/20220804223504.4739-1-dmitrii.bundin.a@gmail.com/
  - Replace hardcoded -g3 with a configurable debug info level

Changes in v3: https://lore.kernel.org/all/20220814002021.16990-1-dmitrii.bundin.a@gmail.com/
  - Make -g<level> and -gdwarf-split to be set independently
  - Add a separate option to control macro definitions for GCC/Clang

 lib/Kconfig.debug      | 20 ++++++++++++++++++++
 scripts/Makefile.debug | 12 ++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2e24db4bff19..ace6f2eddb56 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -304,6 +304,26 @@ config DEBUG_INFO_REDUCED
 	  DEBUG_INFO build and compile times are reduced too.
 	  Only works with newer gcc versions.
 
+config DEBUG_INFO_LEVEL
+	int "Debug info level"
+	range 1 3
+	default "2"
+	help
+	  Sets the level of how much debug information to generate (-glevel).
+	  Level 1 produces minimal debug information without including information
+	  about local variables. Level 3 includes extra information like macro
+	  definitions. Setting up level 3 will require significantly more disk
+	  space and increase built time.
+
+config DEBUG_MACRO_DEFINITIONS
+	bool "Add macro definitions to debug info"
+	default n
+	help
+	  Generates macro definitions to provide a way to expand macros right
+	  in the debugging session. This information can be used with macro expand,
+	  info macro in gdb. This option is equivalent to setting -g3 in GCC and
+	  -fdebug-macro in Clang.
+
 config DEBUG_INFO_COMPRESSED
 	bool "Compressed debugging information"
 	depends on $(cc-option,-gz=zlib)
diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index 9f39b0130551..29cd04234e75 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -2,8 +2,6 @@ DEBUG_CFLAGS	:=
 
 ifdef CONFIG_DEBUG_INFO_SPLIT
 DEBUG_CFLAGS	+= -gsplit-dwarf
-else
-DEBUG_CFLAGS	+= -g
 endif
 
 ifndef CONFIG_AS_IS_LLVM
@@ -16,6 +14,16 @@ dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
 DEBUG_CFLAGS	+= -gdwarf-$(dwarf-version-y)
 endif
 
+DEBUG_CFLAGS	+= -g$(CONFIG_DEBUG_INFO_LEVEL)
+ifdef CONFIG_DEBUG_MACRO_DEFINITIONS
+ifdef CONFIG_CC_IS_GCC
+DEBUG_CFLAGS	+= -g3
+endif
+ifdef CONFIG_CC_IS_CLANG
+DEBUG_CFLAGS	+= -fdebug-macro
+endif
+endif
+
 ifdef CONFIG_DEBUG_INFO_REDUCED
 DEBUG_CFLAGS	+= -fno-var-tracking
 ifdef CONFIG_CC_IS_GCC
-- 
2.17.1