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Message-ID: <20210104220306.GA1405526@ubuntu-m3-large-x86>
Date: Mon, 4 Jan 2021 15:03:06 -0700
From: Nathan Chancellor <natechancellor@...il.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
Arvind Sankar <nivedita@...m.mit.edu>,
Jakub Jelinek <jakub@...hat.com>,
Fangrui Song <maskray@...gle.com>,
Caroline Tice <cmtice@...gle.com>,
clang-built-linux@...glegroups.com,
Nick Clifton <nickc@...hat.com>,
Michal Marek <michal.lkml@...kovi.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Randy Dunlap <rdunlap@...radead.org>,
"peterz@...radead.org" <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Krzysztof Kozlowski <krzk@...nel.org>,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] Kbuild: make DWARF version a choice
On Thu, Dec 03, 2020 at 05:11:26PM -0800, 'Nick Desaulniers' via Clang Built Linux 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: Fangrui Song <maskray@...gle.com>
> Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> Makefile | 14 ++++++++------
> lib/Kconfig.debug | 21 ++++++++++++++++-----
> 2 files changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a2ded5029084..2430e1ee7c44 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -826,12 +826,14 @@ else
> DEBUG_CFLAGS += -g
> endif
>
> -ifneq ($(LLVM_IAS),1)
> -KBUILD_AFLAGS += -Wa,-gdwarf-2
> -endif
> -
> -ifdef CONFIG_DEBUG_INFO_DWARF4
> -DEBUG_CFLAGS += -gdwarf-4
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
> +ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
> +# Binutils 2.35+ required for -gdwarf-4+ support.
> +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
> +DEBUG_CFLAGS += $(dwarf-aflag)
> +KBUILD_AFLAGS += $(dwarf-aflag)
> endif
>
> ifdef CONFIG_DEBUG_INFO_REDUCED
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 0c7380e36370..04719294a7a3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -256,14 +256,25 @@ config DEBUG_INFO_SPLIT
> to know about the .dwo files and include them.
> Incompatible with older versions of ccache.
>
> +choice
> + prompt "DWARF version"
> + help
> + Which version of DWARF debug info to emit.
> +
> +config DEBUG_INFO_DWARF2
> + bool "Generate DWARF Version 2 debuginfo"
> + help
> + Generate DWARF v2 debug info.
> +
> config DEBUG_INFO_DWARF4
> - bool "Generate dwarf4 debuginfo"
> + bool "Generate DWARF Version 4 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.
> - 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"
> --
> 2.29.2.576.ga3fc446d84-goog
>
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