Re: [PATCH v2] kbuild: add configurable debug info level
From: Fangrui Song
Date: Sun Aug 14 2022 - 01:31:36 EST
On 2022-08-14, Masahiro Yamada wrote:
+CC: Fangrui Song <maskray@xxxxxxxxxx>
On Sun, Aug 14, 2022 at 9:25 AM Dmitrii Bundin
<dmitrii.bundin.a@xxxxxxxxx> wrote:
Provides a way to configure debug info level (-glevel).
Debug level 3 includes extra information such as macro definitions. With
level 3 enabled it's possible to expand macros right from the debugging
session in gdb simplifying debugging when complicated macros involved.
The default level is set to 2 to not change the default build behavior.
GCC -g3 generates macro information (in the .debug_macro section).
In Clang, -g = -g2 = -g3. To generate macro information,
specify -fdebug-macro.
The different choice is known in the initial implementation https://reviews.llvm.org/D16135 .
Not generating macro information for -g3 (i.e. diverging from GCC
behavior) makes some sense to me: -fstandalone-debug will probably be
more suitable as -g3 (it retains some type debug info for C++ (the code
after https://github.com/llvm/llvm-project/blob/b2f31cac28c8a03ceb908b544f5790f4f9f2d9ab/clang/lib/CodeGen/CGDebugInfo.cpp#L2497-L2499).
Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@xxxxxxxxx>
---
Changes in v2: https://lore.kernel.org/all/20220804223504.4739-1-dmitrii.bundin.a@xxxxxxxxx/
- Replace hardcoded -g3 with a configurable debug info level
lib/Kconfig.debug | 11 +++++++++++
scripts/Makefile.debug | 2 +-
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2e24db4bff19..a17c12c20290 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -304,6 +304,17 @@ 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 0 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. Level 0 produces no debug information.
+
We already have CONFIG_DEBUG_INFO_NONE to
disable the debug info.
The combination of CONFIG_DEBUG_INFO=y and
CONFIG_DEBUG_INFO_LEVEL=0 (-g0)
would emulate CONFIG_DEBUG_INFO_NONE ?
Using 'int' does not look sensible to me.
config DEBUG_INFO_COMPRESSED
bool "Compressed debugging information"
depends on $(cc-option,-gz=zlib)
diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index 9f39b0130551..28beffc42e71 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -3,7 +3,7 @@ DEBUG_CFLAGS :=
ifdef CONFIG_DEBUG_INFO_SPLIT
DEBUG_CFLAGS += -gsplit-dwarf
else
-DEBUG_CFLAGS += -g
+DEBUG_CFLAGS += -g$(CONFIG_DEBUG_INFO_LEVEL)
endif
ifndef CONFIG_AS_IS_LLVM
--
2.17.1
I want to consult Fangrui Song for this part.
With this Makefile code, CONFIG_DEBUG_INFO_SPLIT
takes the presidency over CONFIG_DEBUG_INFO_LEVEL.
When CONFIG_DEBUG_INFO_SPLIT is enabled (-gsplit-dwarf),
it always uses the default -g2 level.
CONFIG_DEBUG_INFO_LEVEL is just ignored silently.
It might be sensible in older GCC/Clang behavior because
-gsplit-dwarf implied -g2.
But, with this commit:
https://reviews.llvm.org/D80391
-gsplit-dwarf and -g<level> are orthogonal
for GCC 11+/Clang 12+, correct?
Correct.
I think "splitting debug files" and "debug level"
should be controlled independently.
(but it depends on the compiler version, if I understood correctly)
Before GCC 11 and Clang 12, -gsplit-dwarf implied -g2 (older
-gsplit-dwarf is like today's `-gsplit-dwarf -g2`).
GCC 11 and Clang 12 (https://reviews.llvm.org/D80391) have changed
-gsplit-dwarf to not imply -g2.
For a group of -g0 -g1 -g2, the last option wins. Therefore,
-g0 -gsplit-dwarf => debug info in GCC<11 and Clang<12
-g0 -gsplit-dwarf => no debug info in GCC>=11 and Clang>=12