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Kbuild: make DWARF version a choice 

Adds a default CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT which allows
the implicit default version of DWARF emitted by the toolchain to
progress over time.

Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice, making it
mutually exclusive with CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT. Users
may want to select this if they are using a newer toolchain, but have
consumers of the DWARF debug info that aren't yet ready for newer DWARF
versions' debug info.

Does so in a way that's forward compatible with existing
configs, and makes adding future versions more straightforward. This
patch does not change the current behavior or selection of DWARF
version for users upgrading to kernels with this patch.

GCC since ~4.8 has defaulted to DWARF v4 implicitly, and GCC 11 has
bumped this to v5.

Remove the Kconfig help text  about DWARF v4 being larger.  It's
empirically false for the latest toolchains for x86_64 defconfig, has no
point of reference (I suspect it was DWARF v2 but that's stil
empirically false), and debug info size is not a qualatative measure.

Suggested-by: Arvind Sankar <nivedita@alum.mit.edu>
Suggested-by: Fangrui Song <maskray@google.com>
Suggested-by: Jakub Jelinek <jakub@redhat.com>
Suggested-by: Mark Wielaard <mark@klomp.org>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Nick Desaulniers 2021-02-05 12:22:19 -08:00 committed by Masahiro Yamada
parent 3c4fa46b30
commit a66049e2cf
2 changed files with 29 additions and 8 deletions
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5
Makefile
View File

@ -830,8 +830,9 @@ ifneq ($(LLVM_IAS),1)
KBUILD_AFLAGS += -Wa,-gdwarf-2
endif
ifdef CONFIG_DEBUG_INFO_DWARF4
DEBUG_CFLAGS += -gdwarf-4
ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
endif
ifdef CONFIG_DEBUG_INFO_REDUCED

32
lib/Kconfig.debug
View File

@ -256,13 +256,33 @@ config DEBUG_INFO_SPLIT
to know about the .dwo files and include them.
Incompatible with older versions of ccache.
config DEBUG_INFO_DWARF4
bool "Generate dwarf4 debuginfo"
choice
prompt "DWARF version"
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.
Which version of DWARF debug info to emit.
config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
bool "Rely on the toolchain's implicit default DWARF version"
help
The implicit default version of DWARF debug info produced by a
toolchain changes over time.
This can break consumers of the debug info that haven't upgraded to
support newer revisions, and prevent testing newer versions, but
those should be less common scenarios.
If unsure, say Y.
config DEBUG_INFO_DWARF4
bool "Generate DWARF Version 4 debuginfo"
help
Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
If you have consumers of DWARF debug info that are not ready for
newer revisions of DWARF, you may wish to choose this or have your
config select this.
endchoice # "DWARF version"
config DEBUG_INFO_BTF
bool "Generate BTF typeinfo"