[PATCH v2] kbuild: add configurable debug info level

[PATCH v2] kbuild: add configurable debug info level

[Dmitrii Bundin]

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.

Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@gmail.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

 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.
+
 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

Re: [PATCH v2] kbuild: add configurable debug info level

[Masahiro Yamada]

+CC: Fangrui Song <maskray@google.com>




On Sun, Aug 14, 2022 at 9:25 AM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> 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.
>
> Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@gmail.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
>
>  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?


I think "splitting debug files" and "debug level"
should be controlled independently.
(but it depends on the compiler version, if I understood correctly)






--
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: add configurable debug info level

[Fangrui Song]

On 2022-08-14, Masahiro Yamada wrote:
>+CC: Fangrui Song <maskray@google.com>
>
>
>
>
>On Sun, Aug 14, 2022 at 9:25 AM Dmitrii Bundin
><dmitrii.bundin.a@gmail.com> 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@gmail.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
>>
>>  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

Re: [PATCH v2] kbuild: add configurable debug info level

[Masahiro Yamada]

On Sun, Aug 14, 2022 at 2:31 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2022-08-14, Masahiro Yamada wrote:
> >+CC: Fangrui Song <maskray@google.com>
> >
> >
> >
> >
> >On Sun, Aug 14, 2022 at 9:25 AM Dmitrii Bundin
> ><dmitrii.bundin.a@gmail.com> 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@gmail.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
> >>
> >>  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



Thanks.
I tested GCC 9 on Ubuntu 22.04.
"-g3 -gsplit-dwarf" produces .debug_macro

In old behavior, -gsplit-dwarf upgrades the level, but
does not downgrade it, correct?





 [Old behavior]
     -g0 -gsplit-dwarf  --> level 2      (gsplit-dwarf upgrade 0 to 2)
     -gsplit-dwarf -g0  --> level 0      (the last -g0 wins)
     -g3 -gsplit-dwarf  --> level 3      (gsplit-dwarf does not downgrade)
     -g2 -g3            --> level 3      (the last -g3 wins)
     -g3 -g2            --> level 2      (the last -g2 wins)

 [New behavior]
     -g0 -gsplit-dwarf  --> level 0      (the options are orthogonal)
     -gsplit-dwarf -g0  --> level 0      (the options are orthogonal)
     -g3 -gsplit-dwarf  --> level 3      (the options are orthogonal)
     -g2 -g3            --> level 3      (the last -g3 wins)
     -g3 -g2            --> level 2      (the last -g2 wins)








masahiro@grover:/tmp/foo$ gcc-9 --version
gcc-9 (Ubuntu 9.4.0-5ubuntu1) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

masahiro@grover:/tmp/foo$ rm -f *.dwo
masahiro@grover:/tmp/foo$ gcc-9    -gsplit-dwarf  -o foo  foo.c
masahiro@grover:/tmp/foo$ readelf  -S foo.dwo
There are 9 section headers, starting at offset 0x840:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .debug_info.dwo   PROGBITS         0000000000000000  00000040
       0000000000000217  0000000000000000   E       0     0     1
  [ 2] .debug_abbrev.dwo PROGBITS         0000000000000000  00000257
       00000000000000cb  0000000000000000   E       0     0     1
  [ 3] .debug_line.dwo   PROGBITS         0000000000000000  00000322
       00000000000000e5  0000000000000000   E       0     0     1
  [ 4] .debug_str_o[...] PROGBITS         0000000000000000  00000407
       00000000000000d4  0000000000000000   E       0     0     1
  [ 5] .debug_str.dwo    PROGBITS         0000000000000000  000004db
       00000000000002bd  0000000000000000   E       0     0     1
  [ 6] .symtab           SYMTAB           0000000000000000  00000798
       0000000000000030  0000000000000018           7     2     8
  [ 7] .strtab           STRTAB           0000000000000000  000007c8
       0000000000000001  0000000000000000           0     0     1
  [ 8] .shstrtab         STRTAB           0000000000000000  000007c9
       0000000000000073  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  D (mbind), l (large), p (processor specific)
masahiro@grover:/tmp/foo$ rm -f *.dwo
masahiro@grover:/tmp/foo$ gcc-9  -g3  -gsplit-dwarf  -o foo  foo.c
masahiro@grover:/tmp/foo$ readelf  -S foo.dwo
There are 32 section headers, starting at offset 0x77f8:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .debug_info.dwo   PROGBITS         0000000000000000  00000040
       0000000000000245  0000000000000000   E       0     0     1
  [ 2] .debug_abbrev.dwo PROGBITS         0000000000000000  00000285
       00000000000000ce  0000000000000000   E       0     0     1
  [ 3] .debug_macro.dwo  PROGBITS         0000000000000000  00000353
       000000000000014a  0000000000000000   E       0     0     1
  [ 4] .debug_macro.dwo  PROGBITS         0000000000000000  0000049d
       0000000000000528  0000000000000000           0     0     1
  [ 5] .debug_macro.dwo  PROGBITS         0000000000000000  000009c5
       000000000000001c  0000000000000000           0     0     1
  [ 6] .debug_macro.dwo  PROGBITS         0000000000000000  000009e1
       000000000000000c  0000000000000000           0     0     1
  [ 7] .debug_macro.dwo  PROGBITS         0000000000000000  000009ed
       000000000000010b  0000000000000000           0     0     1
  [ 8] .debug_macro.dwo  PROGBITS         0000000000000000  00000af8
       0000000000000010  0000000000000000           0     0     1
  [ 9] .debug_macro.dwo  PROGBITS         0000000000000000  00000b08
       0000000000000033  0000000000000000           0     0     1
  [10] .debug_macro.dwo  PROGBITS         0000000000000000  00000b3b
       0000000000000143  0000000000000000           0     0     1
  [11] .debug_macro.dwo  PROGBITS         0000000000000000  00000c7e
       0000000000000056  0000000000000000           0     0     1
  [12] .debug_macro.dwo  PROGBITS         0000000000000000  00000cd4
       0000000000000021  0000000000000000           0     0     1
  [13] .debug_macro.dwo  PROGBITS         0000000000000000  00000cf5
       0000000000000037  0000000000000000           0     0     1
  [14] .debug_macro.dwo  PROGBITS         0000000000000000  00000d2c
       000000000000000b  0000000000000000           0     0     1
  [15] .debug_macro.dwo  PROGBITS         0000000000000000  00000d37
       0000000000000068  0000000000000000           0     0     1
  [16] .debug_macro.dwo  PROGBITS         0000000000000000  00000d9f
       000000000000000c  0000000000000000           0     0     1
  [17] .debug_macro.dwo  PROGBITS         0000000000000000  00000dab
       0000000000000048  0000000000000000           0     0     1
  [18] .debug_macro.dwo  PROGBITS         0000000000000000  00000df3
       00000000000000a8  0000000000000000           0     0     1
  [19] .debug_macro.dwo  PROGBITS         0000000000000000  00000e9b
       000000000000000b  0000000000000000           0     0     1
  [20] .debug_macro.dwo  PROGBITS         0000000000000000  00000ea6
       0000000000000023  0000000000000000           0     0     1
  [21] .debug_macro.dwo  PROGBITS         0000000000000000  00000ec9
       0000000000000030  0000000000000000           0     0     1
  [22] .debug_macro.dwo  PROGBITS         0000000000000000  00000ef9
       0000000000000020  0000000000000000           0     0     1
  [23] .debug_macro.dwo  PROGBITS         0000000000000000  00000f19
       000000000000001d  0000000000000000           0     0     1
  [24] .debug_macro.dwo  PROGBITS         0000000000000000  00000f36
       0000000000000020  0000000000000000           0     0     1
  [25] .debug_macro.dwo  PROGBITS         0000000000000000  00000f56
       0000000000000059  0000000000000000           0     0     1
  [26] .debug_line.dwo   PROGBITS         0000000000000000  00000faf
       0000000000000255  0000000000000000   E       0     0     1
  [27] .debug_str_o[...] PROGBITS         0000000000000000  00001204
       0000000000000bd4  0000000000000000   E       0     0     1
  [28] .debug_str.dwo    PROGBITS         0000000000000000  00001dd8
       0000000000005721  0000000000000000   E       0     0     1
  [29] .symtab           SYMTAB           0000000000000000  00007500
       0000000000000270  0000000000000018          30    26     8
  [30] .strtab           STRTAB           0000000000000000  00007770
       0000000000000001  0000000000000000           0     0     1
  [31] .shstrtab         STRTAB           0000000000000000  00007771
       0000000000000084  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  D (mbind), l (large), p (processor specific)














-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] kbuild: add configurable debug info level

[Dmitrii Bundin]

> We already have CONFIG_DEBUG_INFO_NONE to
> disable the debug info.

Thanks for pointing this out. Indeed providing another way of
disabling debug info does not look reasonable to me.
So only it makes sense to set only 1, 2 or 3 debug levels.

> Using 'int' does not look sensible to me.

Could you please give a hint why?
My intention to choose int was to provide a boundary with range on the
DEBUG_INFO_LEVEL option to choose only acceptable ones.

On Sun, Aug 14, 2022 at 8:31 AM Fangrui Song <maskray@google.com> wrote:
> In Clang, -g = -g2 = -g3. To generate macro information,
> specify -fdebug-macro.
Thanks.
I would propose to add another config option like
DEBUG_MACRO_DEFINITIONS to turn on macro information for GCC/Clang.
For GCC it would be -g3, for Clang -fdebug-macro.

> 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

I would add a note that when selecting -gdwarf-<level> gcc also
implicitly sets -g2 (at least in older versions).
It seems reasonable to me to put the DEBUG_LEVEL_INFO setting at the
very bottom to prevent it from overriding implicitly.

What do you think?

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

[Dmitrii Bundin]

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@gmail.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

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Masahiro Yamada]

On Mon, Aug 15, 2022 at 10:34 AM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> wrote:
>
> 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.




I am not sure if DEBUG_INFO_LEVEL is useful
because the macro debug data is now enabled
by DEBUG_MACRO_DEFINITIONS.

-g1 is only possible via DEBUG_INFO_LEVEL, but
presumably it is not your main interest
(and not sure if there is anybody interested)
because the main motivation for your v1
is to generate macro debug data.


BTW, DEBUG_INFO_MACRO might be more consistent
(as the others are prefixed DEBUG_INFO_*), but that might
be just my personal preference.








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


--
Best Regards
Masahiro Yamada

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Dmitrii Bundin]

On Thu, Aug 18, 2022 at 7:14 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> -g1 is only possible via DEBUG_INFO_LEVEL, but
> presumably it is not your main interest
> (and not sure if there is anybody interested)
> because the main motivation for your v1
> is to generate macro debug data.

I tested the build process with -g1 and it turned out to generate an
image that is 20% lesser in size.
This is indeed not really my use-case, but are you sure it might not
be helpful in general?

The reason to add DEBUG_INFO_LEVEL was also motivated by the
GCC11+/Clang12+ behavior of -gsplit-dwarf to provide an orthogonal
debug level config.
"The later -g<level> wins" behavior in turns works identically for
both older and newer compiler versions so such an implementation
provides version independent build behavior.
Testing on gcc-11, -gdwarf-<level>/-gdwarf still implies -g2.
It seemed a clearer way to me to explicitly set a debug level that
just wins instead of relying on implicits.

Regards
Dmitrii

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Nick Desaulniers]

On Sun, Aug 14, 2022 at 6:34 PM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> wrote:
>
> 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@gmail.com>
> ---
>
> Changes in v2: https://lore.kernel.org/all/20220804223504.4739-1-dmitrii.bundin.a@gmail.com/

Is any of this really necessary?  It seems like a great way to bloat
vmlinux artifacts built with CONFIG_DEBUG_INFO even further.  The
above link mentions "when debugging with GDB."  In that case, please
don't add new Kconfigs for these; just set -g3 when
CONFIG_GDB_SCRIPTS=y.

-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Dmitrii Bundin]

On Fri, Aug 19, 2022 at 8:42 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> Is any of this really necessary?

Consider the case if CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y.
Prior to GCC11/Clang12 -gsplit-dwarf implied -g2. So on newer
compilers with -gsplit-dwarf in use there would be no debug symbols
produced. -gdwarf-4/5 still implies -g2, but in case
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y neither of the options are
set. So it seems like a reasonable choice to provide a debug info
level config that would explicitly set the level without relying on
implicits. The default value of the config is set to -g2 to not change
the build behavior that was before introducing the option. And it
works for both older and newer versions of GCC/Clang in the same way.
The benefits of the -g1 option are indeed questionable except that it
produces an image with ~20% less in size.

> It seems like a great way to bloat
> vmlinux artifacts built with CONFIG_DEBUG_INFO even further.
The defaults were chosen to not change the build behavior that was
before introducing the options. Or did you mean something else?

> The
> above link mentions "when debugging with GDB."  In that case, please
> don't add new Kconfigs for these; just set -g3 when
> CONFIG_GDB_SCRIPTS=y.

CONFIG_GDB_SCRIPTS does not necessarily mean that -g3 is wanted, -g2
(default) is usually a reasonable choice. The -g3 option is very
useful when debugging macro-intensive code, but requires much more
disk space to build. I documented it explicitly in the help section of
DEBUG_INFO_LEVEL. GCC and Clang use different options to include macro
definitions so it was handled depending on the compiler used.

Regards
Dmitrii

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Nick Desaulniers]

On Fri, Aug 19, 2022 at 3:52 PM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> wrote:
>
> On Fri, Aug 19, 2022 at 8:42 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > Is any of this really necessary?
>
> Consider the case if CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y.
> Prior to GCC11/Clang12 -gsplit-dwarf implied -g2. So on newer
> compilers with -gsplit-dwarf in use there would be no debug symbols
> produced.

```
diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index 9f39b0130551..a881954c1382 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -1,7 +1,7 @@
 DEBUG_CFLAGS   :=

 ifdef CONFIG_DEBUG_INFO_SPLIT
-DEBUG_CFLAGS   += -gsplit-dwarf
+DEBUG_CFLAGS   += -gsplit-dwarf -g2
 else
 DEBUG_CFLAGS   += -g
 endif
```

or perhaps that simply needs to be `-g -gsplit-dwarf`?  In which case,
that if/else could just be re-arranged.

> -gdwarf-4/5 still implies -g2, but in case
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y neither of the options are
> set.

-g is set, which has an implicit default level.

> So it seems like a reasonable choice to provide a debug info
> level config that would explicitly set the level without relying on
> implicits. The default value of the config is set to -g2 to not change
> the build behavior that was before introducing the option. And it
> works for both older and newer versions of GCC/Clang in the same way.
> The benefits of the -g1 option are indeed questionable except that it
> produces an image with ~20% less in size.

Until there's a concrete need, YAGNI.

>
> > It seems like a great way to bloat
> > vmlinux artifacts built with CONFIG_DEBUG_INFO even further.
> The defaults were chosen to not change the build behavior that was
> before introducing the options. Or did you mean something else?
>
> > The
> > above link mentions "when debugging with GDB."  In that case, please
> > don't add new Kconfigs for these; just set -g3 when
> > CONFIG_GDB_SCRIPTS=y.
>
> CONFIG_GDB_SCRIPTS does not necessarily mean that -g3 is wanted, -g2
> (default) is usually a reasonable choice. The -g3 option is very
> useful when debugging macro-intensive code, but requires much more
> disk space to build. I documented it explicitly in the help section of
> DEBUG_INFO_LEVEL. GCC and Clang use different options to include macro
> definitions so it was handled depending on the compiler used.

Honestly, I really don't think we need to be wrapping every compiler
command line flag under the sun in a kconfig option.

-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Nick Desaulniers]

On Mon, Aug 22, 2022 at 9:45 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> > So it seems like a reasonable choice to provide a debug info
> > level config that would explicitly set the level without relying on
> > implicits. The default value of the config is set to -g2 to not change
> > the build behavior that was before introducing the option. And it
> > works for both older and newer versions of GCC/Clang in the same way.
> > The benefits of the -g1 option are indeed questionable except that it
> > produces an image with ~20% less in size.
>
> Until there's a concrete need, YAGNI.

Or add -g1 to CONFIG_DEBUG_INFO_REDUCED.
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Dmitrii Bundin]

On Tue, Aug 23, 2022 at 12:36 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> or perhaps that simply needs to be `-g -gsplit-dwarf`?  In which case,
> that if/else could just be re-arranged.

How about simply assigning DEBUG_CFLAGS   := -g at the very beginning
without any conditions? This would provide the default with the
possibility of overriding later and -gsplit-dwarf does not necessarily
come with -g implicitly.

> Honestly, I really don't think we need to be wrapping every compiler
> command line flag under the sun in a kconfig option.

This indeed sounds reasonable to me. So the key point here is to not
bloat the kconfig with options related to every compiler flag. But I
think it still might be useful to provide some option that would
include sort of full debug information compilers may produce. With
this approach there would be, in fact 3 different levels of debug
information supported by Kconfig: reduced, default and full. The full
level would increase everything like -g3, and -fdebug-macro for Clang,
and probably others.

> Or add -g1 to CONFIG_DEBUG_INFO_REDUCED.

I ran some tests and there was indeed some decrease in size. That
combination probably might be useful.

Any thoughts?

Regards
Dmitrii

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Peter Zijlstra]

On Sat, Aug 20, 2022 at 01:52:04AM +0300, Dmitrii Bundin wrote:
> On Fri, Aug 19, 2022 at 8:42 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > Is any of this really necessary?
> 
> Consider the case if CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y.

Can I just say I *HATE* that thing? It uesd to be I could do:

../scripts/config --enable DEBUG_INFO

and I'd get a debug-info build, now I gotta use that horrible piece of
crap you just mentioned which I mis-type at least once every single
time.

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Nick Desaulniers]

On Mon, Aug 22, 2022 at 3:42 PM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> wrote:
>
> On Tue, Aug 23, 2022 at 12:36 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > or perhaps that simply needs to be `-g -gsplit-dwarf`?  In which case,
> > that if/else could just be re-arranged.
>
> How about simply assigning DEBUG_CFLAGS   := -g at the very beginning
> without any conditions? This would provide the default with the
> possibility of overriding later and -gsplit-dwarf does not necessarily
> come with -g implicitly.

SGTM; I'd accept such a patch.

> > Honestly, I really don't think we need to be wrapping every compiler
> > command line flag under the sun in a kconfig option.
>
> This indeed sounds reasonable to me. So the key point here is to not
> bloat the kconfig with options related to every compiler flag. But I
> think it still might be useful to provide some option that would
> include sort of full debug information compilers may produce. With
> this approach there would be, in fact 3 different levels of debug
> information supported by Kconfig: reduced, default and full. The full
> level would increase everything like -g3, and -fdebug-macro for Clang,
> and probably others.

Has anyone asked for that though?  It seems like your intent with this
patch is to fix the surprising+user hostile behavior of compilers
requiring -g to be used when -gsplit-dwarf is used.

If someone using GDB_SCRIPTS or KGDB was like "man, I wish I could
debug macros" then sure I'd be more likely to accept this. Without the
need, this is just wrapping every compiler option in a kconfig, which
frustrates randconfig testing bots.  This will slow them down and
bloat their artifacts when randconfig selects -g3, so I'd like someone
to come forward saying they need this and why.

>
> > Or add -g1 to CONFIG_DEBUG_INFO_REDUCED.
>
> I ran some tests and there was indeed some decrease in size. That
> combination probably might be useful.
>
> Any thoughts?

I think there's also -gmlt; when that is preferable to -g1 IDK. Why
either of those weren't used in the first place, IDK.

The help text in DEBUG_INFO_REDUCED in lib/Kconfig.debug makes it
sound like -gmlt is what is wanted.  Maybe that should be updated.

But I think DEBUG_INFO_REDUCED is redundant if we were to accept
DEBUG_INFO_LEVEL. Both don't need to exist IMO.
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Masahiro Yamada]

On Tue, Aug 23, 2022 at 7:42 AM Dmitrii Bundin
<dmitrii.bundin.a@gmail.com> wrote:
>
> On Tue, Aug 23, 2022 at 12:36 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > or perhaps that simply needs to be `-g -gsplit-dwarf`?  In which case,
> > that if/else could just be re-arranged.
>
> How about simply assigning DEBUG_CFLAGS   := -g at the very beginning
> without any conditions? This would provide the default with the
> possibility of overriding later and -gsplit-dwarf does not necessarily
> come with -g implicitly.

This was fixed by commit 32ef9e5054ec0321b9336058c58ec749e9c6b0fe,
which is now in the mainline.




> > Honestly, I really don't think we need to be wrapping every compiler
> > command line flag under the sun in a kconfig option.
>
> This indeed sounds reasonable to me. So the key point here is to not
> bloat the kconfig with options related to every compiler flag. But I
> think it still might be useful to provide some option that would
> include sort of full debug information compilers may produce. With
> this approach there would be, in fact 3 different levels of debug
> information supported by Kconfig: reduced, default and full. The full
> level would increase everything like -g3, and -fdebug-macro for Clang,
> and probably others.


I think that would be much saner than this patch.



CONFIG_DEBUG_INFO_LEVEL is a direct way to specify the debug level.

CONFIG_DEBUG_MACRO_DEFINITIONS is feature-driven.

Do not mix two different ways.






CONFIG_DEBUG_INFO_LEVEL is here just because Andrew Morton suggested that.


The debug level is compiler-specific. There is no guarantee
that there is a common range.


The debug level range of GCC is 0-3.
Clang accepts 3, but -g3 has no effect.
The debug level range of Rustc is 0-2.

See how badly scripts/Makefile.debug looks in linux-next.





How should Rustc behave for CONFIG_DEBUG_INFO_LEVEL=3 ?

-Cdebuginfo=3 is a compile error.

  RUSTC L rust/core.o
error: debug info level needs to be between 0-2 (instead was `3`)



You cannot directly specify the debug level number given that
we support multiple compilers with different policy for
debug level options.






> > Or add -g1 to CONFIG_DEBUG_INFO_REDUCED.
>
> I ran some tests and there was indeed some decrease in size. That
> combination probably might be useful.
>
> Any thoughts?
>
> Regards
> Dmitrii





-- 
Best Regards
Masahiro Yamada

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Masahiro Yamada]

On Fri, Sep 30, 2022 at 6:06 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Tue, Aug 23, 2022 at 7:42 AM Dmitrii Bundin
> <dmitrii.bundin.a@gmail.com> wrote:
> >
> > On Tue, Aug 23, 2022 at 12:36 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > or perhaps that simply needs to be `-g -gsplit-dwarf`?  In which case,
> > > that if/else could just be re-arranged.
> >
> > How about simply assigning DEBUG_CFLAGS   := -g at the very beginning
> > without any conditions? This would provide the default with the
> > possibility of overriding later and -gsplit-dwarf does not necessarily
> > come with -g implicitly.
>
> This was fixed by commit 32ef9e5054ec0321b9336058c58ec749e9c6b0fe,
> which is now in the mainline.
>
>
>
>
> > > Honestly, I really don't think we need to be wrapping every compiler
> > > command line flag under the sun in a kconfig option.
> >
> > This indeed sounds reasonable to me. So the key point here is to not
> > bloat the kconfig with options related to every compiler flag. But I
> > think it still might be useful to provide some option that would
> > include sort of full debug information compilers may produce. With
> > this approach there would be, in fact 3 different levels of debug
> > information supported by Kconfig: reduced, default and full. The full
> > level would increase everything like -g3, and -fdebug-macro for Clang,
> > and probably others.
>
>
> I think that would be much saner than this patch.
>
>
>
> CONFIG_DEBUG_INFO_LEVEL is a direct way to specify the debug level.
>
> CONFIG_DEBUG_MACRO_DEFINITIONS is feature-driven.
>
> Do not mix two different ways.
>
>
>
>
>
>
> CONFIG_DEBUG_INFO_LEVEL is here just because Andrew Morton suggested that.
>
>
> The debug level is compiler-specific. There is no guarantee
> that there is a common range.
>
>
> The debug level range of GCC is 0-3.
> Clang accepts 3, but -g3 has no effect.
> The debug level range of Rustc is 0-2.
>
> See how badly scripts/Makefile.debug looks in linux-next.
>
>
>
>
>
> How should Rustc behave for CONFIG_DEBUG_INFO_LEVEL=3 ?
>
> -Cdebuginfo=3 is a compile error.
>
>   RUSTC L rust/core.o
> error: debug info level needs to be between 0-2 (instead was `3`)
>
>
>
> You cannot directly specify the debug level number given that
> we support multiple compilers with different policy for
> debug level options.
>
>
>
>
>
>
> > > Or add -g1 to CONFIG_DEBUG_INFO_REDUCED.
> >
> > I ran some tests and there was indeed some decrease in size. That
> > combination probably might be useful.
> >
> > Any thoughts?
> >
> > Regards
> > Dmitrii
>
>
>
>
>
> --
> Best Regards
> Masahiro Yamada






I proposed to do a ground-work like the following first.
https://patchwork.kernel.org/project/linux-kbuild/patch/20220930085351.2648034-1-masahiroy@kernel.org/



On top of that, it is easier to add CONFIG_DEBUG_INFO_FULL or whatever.


And, -g1 for CONFIG_DEBUG_INFO_REDUCED if you think it is worthwhile.



-- 
Best Regards
Masahiro Yamada

Re: [PATCH v3] kbuild: add debug level and macro defs options

[Dmitrii Bundin]

Hi Masahiro,

> On top of that, it is easier to add CONFIG_DEBUG_INFO_FULL or whatever.
As per the prior discussion, Nick has convinced me that configuring an
additional choice for a full debug info might cause more problems that
it solves in general.

>And, -g1 for CONFIG_DEBUG_INFO_REDUCED if you think it is worthwhile.
This indeed would shrink the image size, but with this option enabled
there would be no information about local variables which might
surprise users of the option. So I don't really think it is
worthwhile.

Regards,
Dmitrii.