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SubjectRe: [PATCH v7 1/2] Kbuild: make DWARF version a choice
On Fri, Jan 29, 2021 at 04:44:00PM -0800, Nick Desaulniers wrote:
> Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice which is
> the default. Does so in a way that's forward compatible with existing
> configs, and makes adding future versions more straightforward.
>
> GCC since ~4.8 has defaulted to this DWARF version implicitly.
>
> Suggested-by: Arvind Sankar <nivedita@alum.mit.edu>
> Suggested-by: Fangrui Song <maskray@google.com>
> Suggested-by: Nathan Chancellor <nathan@kernel.org>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

One comment below:

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> Makefile | 5 ++---
> lib/Kconfig.debug | 16 +++++++++++-----
> 2 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 95ab9856f357..d2b4980807e0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -830,9 +830,8 @@ ifneq ($(LLVM_IAS),1)
> KBUILD_AFLAGS += -Wa,-gdwarf-2

It is probably worth a comment somewhere that assembly files will still
have DWARF v2.

> endif
>
> -ifdef CONFIG_DEBUG_INFO_DWARF4
> -DEBUG_CFLAGS += -gdwarf-4
> -endif
> +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
>
> 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 e906ea906cb7..94c1a7ed6306 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -256,13 +256,19 @@ 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_DWARF4
> - bool "Generate dwarf4 debuginfo"
> + bool "Generate DWARF Version 4 debuginfo"
> 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"
> --
> 2.30.0.365.g02bc693789-goog
>

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