Re: [PATCH 5.0 070/246] kbuild: make -r/-R effective in top Makefile for old Make versions

[Masahiro Yamada]

Hi.


On Thu, Apr 4, 2019 at 6:11 PM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> 5.0-stable review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> [ Upstream commit 3812b8c5c5d527239ac015f1f2c7654da7fcfbba ]


Some people complaint about this commit.

If you backport this,
could you please backport the following two as well?

2b50f7ab63685cd247e32ad321f7338ed130d3d5
688931a5ad4e55ba0c215248ba510cd67bc3afb4


Thanks.
Masahiro Yamada






> Adding -rR to MAKEFLAGS is important because we do not want to
> be bothered by built-in implicit rules or variables.
>
> One problem that used to exist in older GNU Make versions is
>
>   MAKEFLAGS += -rR
>
> ... does not become effective in the current Makefile. When you are
> building with O= option, it becomes effective in the top Makefile
> since it recurses via 'sub-make' target. Otherwise, the top Makefile
> tries implicit rules. That is why we explicitly add empty rules for
> Makefiles, but we often miss to do that.
>
> In fact, adding -d option to older GNU Make versions shows it is
> trying a bunch of implicit pattern rules.
>
>  Considering target file `scripts/Makefile.kcov'.
>   Looking for an implicit rule for `scripts/Makefile.kcov'.
>   Trying pattern rule with stem `Makefile.kcov'.
>   Trying implicit prerequisite `scripts/Makefile.kcov.o'.
>   Trying pattern rule with stem `Makefile.kcov'.
>   Trying implicit prerequisite `scripts/Makefile.kcov.c'.
>   Trying pattern rule with stem `Makefile.kcov'.
>   Trying implicit prerequisite `scripts/Makefile.kcov.cc'.
>   Trying pattern rule with stem `Makefile.kcov'.
>   Trying implicit prerequisite `scripts/Makefile.kcov.C'.
>   ...
>
> This issue was fixed by GNU Make commit 58dae243526b ("[Savannah #20501]
> Handle adding -r/-R to MAKEFLAGS in the makefile"). So, it is no longer
> a problem if you use GNU Make 4.0 or later. However, older versions are
> still widely used.
>
> So, I decided to patch the kernel Makefile to invoke sub-make regardless
> of O= option. This will allow further cleanups.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  Makefile | 48 ++++++++++++++++++++++++++----------------------
>  1 file changed, 26 insertions(+), 22 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 6d542aede778..1bc6749f5254 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -15,19 +15,6 @@ NAME = Shy Crocodile
>  PHONY := _all
>  _all:
>
> -# Do not use make's built-in rules and variables
> -# (this increases performance and avoids hard-to-debug behaviour)
> -MAKEFLAGS += -rR
> -
> -# Avoid funny character set dependencies
> -unexport LC_ALL
> -LC_COLLATE=C
> -LC_NUMERIC=C
> -export LC_COLLATE LC_NUMERIC
> -
> -# Avoid interference with shell env settings
> -unexport GREP_OPTIONS
> -
>  # We are using a recursive build, so we need to do a little thinking
>  # to get the ordering right.
>  #
> @@ -44,6 +31,21 @@ unexport GREP_OPTIONS
>  # descending is started. They are now explicitly listed as the
>  # prepare rule.
>
> +ifneq ($(sub-make-done),1)
> +
> +# Do not use make's built-in rules and variables
> +# (this increases performance and avoids hard-to-debug behaviour)
> +MAKEFLAGS += -rR
> +
> +# Avoid funny character set dependencies
> +unexport LC_ALL
> +LC_COLLATE=C
> +LC_NUMERIC=C
> +export LC_COLLATE LC_NUMERIC
> +
> +# Avoid interference with shell env settings
> +unexport GREP_OPTIONS
> +
>  # Beautify output
>  # ---------------------------------------------------------------------------
>  #
> @@ -112,7 +114,6 @@ export quiet Q KBUILD_VERBOSE
>
>  # KBUILD_SRC is not intended to be used by the regular user (for now),
>  # it is set on invocation of make with KBUILD_OUTPUT or O= specified.
> -ifeq ($(KBUILD_SRC),)
>
>  # OK, Make called in directory where kernel src resides
>  # Do we want to locate output files in a separate directory?
> @@ -142,6 +143,13 @@ $(if $(KBUILD_OUTPUT),, \
>  # 'sub-make' below.
>  MAKEFLAGS += --include-dir=$(CURDIR)
>
> +else
> +
> +# Do not print "Entering directory ..." at all for in-tree build.
> +MAKEFLAGS += --no-print-directory
> +
> +endif # ifneq ($(KBUILD_OUTPUT),)
> +
>  PHONY += $(MAKECMDGOALS) sub-make
>
>  $(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
> @@ -149,16 +157,12 @@ $(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
>
>  # Invoke a second make in the output directory, passing relevant variables
>  sub-make:
> -       $(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \
> +       $(Q)$(MAKE) sub-make-done=1 \
> +       $(if $(KBUILD_OUTPUT),-C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR)) \
>         -f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))
>
> -# Leave processing to above invocation of make
> -skip-makefile := 1
> -endif # ifneq ($(KBUILD_OUTPUT),)
> -endif # ifeq ($(KBUILD_SRC),)
> -
> +else # sub-make-done
>  # We process the rest of the Makefile if this is the final invocation of make
> -ifeq ($(skip-makefile),)
>
>  # Do not print "Entering directory ...",
>  # but we want to display it when entering to the output directory
> @@ -1759,7 +1763,7 @@ $(cmd_files): ;   # Do not try to update included dependency files
>
>  endif   # ifeq ($(config-targets),1)
>  endif   # ifeq ($(mixed-targets),1)
> -endif  # skip-makefile
> +endif   # sub-make-done
>
>  PHONY += FORCE
>  FORCE:
> --
> 2.19.1
>
>
>


-- 
Best Regards
Masahiro Yamada