linux-kernel - Re: [PATCH v5 2/3] Kbuild: make DWARF version a choice

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Message-ID: <20210115220528.pyyr7hls2lgca3o7@google.com>
Date:   Fri, 15 Jan 2021 14:05:28 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org,
        Jakub Jelinek <jakub@...hat.com>,
        Caroline Tice <cmtice@...gle.com>,
        Nick Clifton <nickc@...hat.com>, Yonghong Song <yhs@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH v5 2/3] Kbuild: make DWARF version a choice

On 2021-01-15, Sedat Dilek wrote:
>On Fri, Jan 15, 2021 at 10:06 PM Nick Desaulniers
><ndesaulniers@...gle.com> wrote:
>>
>> Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
>> explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
>> way that's forward compatible with existing configs, and makes adding
>> future versions more straightforward.
>>
>> Suggested-by: Arvind Sankar <nivedita@...m.mit.edu>
>> Suggested-by: Fangrui Song <maskray@...gle.com>
>> Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
>> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
>> ---
>>  Makefile          | 13 ++++++-------
>>  lib/Kconfig.debug | 21 ++++++++++++++++-----
>>  2 files changed, 22 insertions(+), 12 deletions(-)
>>
>> diff --git a/Makefile b/Makefile
>> index d49c3f39ceb4..4eb3bf7ee974 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -826,13 +826,12 @@ else
>>  DEBUG_CFLAGS   += -g
>>  endif
>>
>> -ifneq ($(LLVM_IAS),1)
>> -KBUILD_AFLAGS  += -Wa,-gdwarf-2
>> -endif
>> -
>> -ifdef CONFIG_DEBUG_INFO_DWARF4
>> -DEBUG_CFLAGS   += -gdwarf-4
>> -endif
>> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
>> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
>> +DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)
>> +# Binutils 2.35+ required for -gdwarf-4+ support.
>> +dwarf-aflag    := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
>> +KBUILD_AFLAGS  += $(dwarf-aflag)
>>
>>  ifdef CONFIG_DEBUG_INFO_REDUCED
>>  DEBUG_CFLAGS   += $(call cc-option, -femit-struct-debug-baseonly) \
>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> index dd7d8d35b2a5..e80770fac4f0 100644
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -256,13 +256,24 @@ config DEBUG_INFO_SPLIT
>>           to know about the .dwo files and include them.
>>           Incompatible with older versions of ccache.
>>
>> +choice
>> +       prompt "DWARF version"
>
>Here you use "DWARF version" so keep this for v2 and v4.
>
>> +       help
>> +         Which version of DWARF debug info to emit.
>> +
>> +config DEBUG_INFO_DWARF2
>> +       bool "Generate DWARF Version 2 debuginfo"
>
>s/DWARF Version/DWARF version
>
>> +       help
>> +         Generate DWARF v2 debug info.
>> +
>>  config DEBUG_INFO_DWARF4
>> -       bool "Generate dwarf4 debuginfo"
>> +       bool "Generate DWARF Version 4 debuginfo"
>
>Same here: s/DWARF Version/DWARF version

DWARF Version 2 is fine and preferable.

I have checked DWARF Version 2/3/4/5 specifications.
"DWARF Version 2" is the official way that version is referred to...

>
>- Sedat -
>
>>         help
>> -         Generate dwarf4 debug info. This requires recent versions
>> -         of gcc and gdb. It makes the debug information larger.
>> -         But it significantly improves the success of resolving
>> -         variables in gdb on optimized code.
>> +         Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
>> +         It makes the debug information larger, but it significantly
>> +         improves the success of resolving variables in gdb on optimized code.
>> +
>> +endchoice # "DWARF version"
>>
>>  config DEBUG_INFO_BTF
>>         bool "Generate BTF typeinfo"
>> --
>> 2.30.0.284.gd98b1dd5eaa7-goog
>>