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    Subject[PATCH v9 2/3] Kbuild: make DWARF version a choice
    From
    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>
    Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
    ---
    Makefile | 5 +++--
    lib/Kconfig.debug | 30 +++++++++++++++++++++++++-----
    2 files changed, 28 insertions(+), 7 deletions(-)

    diff --git a/Makefile b/Makefile
    index 28019532e55a..a7eee28dd091 100644
    --- a/Makefile
    +++ b/Makefile
    @@ -829,8 +829,9 @@ 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
    diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
    index e906ea906cb7..3ac450346dbe 100644
    --- a/lib/Kconfig.debug
    +++ b/lib/Kconfig.debug
    @@ -256,13 +256,33 @@ 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_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 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+.
    +
    + 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"
    --
    2.30.0.365.g02bc693789-goog
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