From: Fangrui Song <maskray@google.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
Nathan Chancellor <natechancellor@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Sedat Dilek <sedat.dilek@gmail.com>,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org,
Jakub Jelinek <jakub@redhat.com>,
Caroline Tice <cmtice@google.com>,
Nick Clifton <nickc@redhat.com>, Yonghong Song <yhs@fb.com>,
Jiri Olsa <jolsa@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH v5 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4
Date: Fri, 15 Jan 2021 13:59:58 -0800 [thread overview]
Message-ID: <20210115215958.3cqewpk7hycfr3hm@google.com> (raw)
In-Reply-To: <20210115210616.404156-2-ndesaulniers@google.com>
On 2021-01-15, Nick Desaulniers wrote:
>From: Masahiro Yamada <masahiroy@kernel.org>
>
>The -gdwarf-4 flag is supported by GCC 4.5+, and also by Clang.
>
>You can see it at https://godbolt.org/z/6ed1oW
>
> For gcc 4.5.3 pane, line 37: .value 0x4
> For clang 10.0.1 pane, line 117: .short 4
>
>Given Documentation/process/changes.rst stating GCC 4.9 is the minimal
>version, this cc-option is unneeded.
>
>Note
>----
>
>CONFIG_DEBUG_INFO_DWARF4 controls the DWARF version only for C files.
>
>As you can see in the top Makefile, -gdwarf-4 is only passed to CFLAGS.
>
> ifdef CONFIG_DEBUG_INFO_DWARF4
> DEBUG_CFLAGS += -gdwarf-4
> endif
>
>This flag is used when compiling *.c files.
>
>On the other hand, the assembler is always given -gdwarf-2.
>
> KBUILD_AFLAGS += -Wa,-gdwarf-2
>
>Hence, the debug info that comes from *.S files is always DWARF v2.
>This is simply because GAS supported only -gdwarf-2 for a long time.
>
>Recently, GAS gained the support for --dwarf-[3|4|5] options. [1]
The gas commit description has a typo. The supported options are -gdwarf-[345] or --gdwarf-[345].
-gdwarf2 and --gdwarf2 are kept for compatibility.
Looks good otherwise.
>And, also we have Clang integrated assembler. So, the debug info
>for *.S files might be improved if we want.
>
>In my understanding, the current code is intentional, not a bug.
>
>[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=31bf18645d98b4d3d7357353be840e320649a67d
>
>Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
>Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
>---
> lib/Kconfig.debug | 1 -
> 1 file changed, 1 deletion(-)
>
>diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>index 78361f0abe3a..dd7d8d35b2a5 100644
>--- a/lib/Kconfig.debug
>+++ b/lib/Kconfig.debug
>@@ -258,7 +258,6 @@ config DEBUG_INFO_SPLIT
>
> config DEBUG_INFO_DWARF4
> bool "Generate dwarf4 debuginfo"
>- depends on $(cc-option,-gdwarf-4)
> help
> Generate dwarf4 debug info. This requires recent versions
> of gcc and gdb. It makes the debug information larger.
>--
>2.30.0.284.gd98b1dd5eaa7-goog
>
next prev parent reply other threads:[~2021-01-15 22:00 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-15 21:06 [PATCH v5 0/3] Kbuild: DWARF v5 support Nick Desaulniers
2021-01-15 21:06 ` [PATCH v5 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4 Nick Desaulniers
2021-01-15 21:47 ` Sedat Dilek
2021-01-15 21:51 ` Nick Desaulniers
2021-01-15 23:54 ` Masahiro Yamada
2021-01-20 5:57 ` Masahiro Yamada
2021-01-15 21:59 ` Fangrui Song [this message]
2021-01-15 22:03 ` Sedat Dilek
2021-01-15 21:06 ` [PATCH v5 2/3] Kbuild: make DWARF version a choice Nick Desaulniers
2021-01-15 21:42 ` Sedat Dilek
2021-01-15 22:05 ` Fangrui Song
2021-01-20 20:40 ` Nathan Chancellor
2021-01-21 2:35 ` Sedat Dilek
2021-01-15 21:06 ` [PATCH v5 3/3] Kbuild: implement support for DWARF v5 Nick Desaulniers
2021-01-15 21:45 ` Sedat Dilek
2021-01-15 21:49 ` Nick Desaulniers
2021-01-15 21:57 ` Sedat Dilek
2021-01-15 21:53 ` [PATCH v5 0/3] Kbuild: DWARF v5 support Sedat Dilek
2021-01-15 23:24 ` Yonghong Song
2021-01-15 23:34 ` Nick Desaulniers
2021-01-15 23:42 ` Andrii Nakryiko
2021-01-15 23:43 ` Yonghong Song
2021-01-17 20:15 ` Arnaldo Carvalho de Melo
2021-02-04 1:31 ` Nick Desaulniers
2021-02-04 2:57 ` Andrii Nakryiko
2021-02-04 3:13 ` Nick Desaulniers
2021-02-04 23:54 ` Andrii Nakryiko
2021-02-05 0:04 ` Nick Desaulniers
2021-02-04 8:42 ` Sedat Dilek
2021-02-04 8:59 ` Sedat Dilek
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