Re: [PATCH] kbuild: fix duplicated flags in DEBUG_CFLAGS

[Sedat Dilek <sedat.dilek@gmail.com>]

On Wed, Feb 3, 2021 at 8:53 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Sedat Dilek noticed duplicated debug flags passed when building C
> files with CONFIG_DEBUG_INFO.
>
> I do not know much about his build environment, but yes, Kbuild
> recurses to the top Makefile with some build targets. For example,
> 'make CC=clang bindeb-pkg' reproduces the issue.
>
> With commit 121c5d08d53c ("kbuild: Only add -fno-var-tracking-assignments
> for old GCC versions") applied, DEBUG_CFLAGS is now reset only when
> CONFIG_CC_IS_GCC=y.
>
> Fix it to reset DEBUG_CFLAGS also when using Clang.
>
> Fixes: 121c5d08d53c ("kbuild: Only add -fno-var-tracking-assignments for old GCC versions")
> Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

That fixes the issue for me:

Without patch:

... -Wno-unused-const-variable -g -gdwarf-5 -gz=zlib -g -gdwarf-5
-gz=zlib -pg -mfentry ...

With this patch:
... -Wno-unused-const-variable -g -gdwarf-5 -gz=zlib -pg -mfentry ...

The relevant Kconfigs:

$ grep DEBUG_INFO .config | grep ^CONFIG
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_COMPRESSED=y
CONFIG_DEBUG_INFO_DWARF5=y

Latest make-line:

$ /usr/bin/perf_5.10 stat make V=1 -j4 LLVM=1 LLVM_IAS=1
PAHOLE=/opt/pahole/bin/pahole LOCALVERSION=-4-amd64-clang12-
cfi-pgo KBUILD_VERBOSE=1 KBUILD_BUILD_HOST=iniza
KBUILD_BUILD_USER=sedat.dilek@gmail.com
KBUILD_BUILD_TIMESTAMP=2021-02-03 bindeb-pkg
KDEB_PKGVERSION=5.11.0~rc6-4~bull
seye+dileks1

Feel free to add my...

   Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

Thanks again Masahiro.

- Sedat -

> ---
>
>  Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 3d3f67b98ca2..769a38ee81b9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -811,10 +811,12 @@ KBUILD_CFLAGS     += -ftrivial-auto-var-init=zero
>  KBUILD_CFLAGS  += -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
>  endif
>
> +DEBUG_CFLAGS   :=
> +
>  # Workaround for GCC versions < 5.0
>  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801
>  ifdef CONFIG_CC_IS_GCC
> -DEBUG_CFLAGS   := $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
> +DEBUG_CFLAGS   += $(call cc-ifversion, -lt, 0500, $(call cc-option, -fno-var-tracking-assignments))
>  endif
>
>  ifdef CONFIG_DEBUG_INFO
> --
> 2.27.0
>