Message-ID: <20241127-maize-hippo-of-innovation-ad1c54@buildd>
Date: Wed, 27 Nov 2024 16:29:27 +0100
From: Nicolas Schier <n.schier@....de>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org, cocci@...ia.fr
Subject: Re: [PATCH v2 05/11] kbuild: change working directory to external
 module directory with M=

On Tue, Nov 19, 2024 at 02:02:05AM +0900, Masahiro Yamada wrote:
> On Mon, Nov 18, 2024 at 11:47 PM Nicolas Schier <n.schier@....de> wrote:
> >
> > On Sun, Nov 10, 2024 at 10:34:33AM +0900, Masahiro Yamada wrote:
> > > Currently, Kbuild always operates in the output directory of the kernel,
> > > even when building external modules. This increases the risk of external
> > > module Makefiles attempting to write to the kernel directory.
> > >
> > > This commit switches the working directory to the external module
> > > directory, allowing the removal of the $(KBUILD_EXTMOD)/ prefix from
> > > some build artifacts.
> > >
> > > The command for building external modules maintains backward
> > > compatibility, but Makefiles that rely on working in the kernel
> > > directory may break. In such cases, $(objtree) and $(srctree) should
> > > be used to refer to the output and source directories of the kernel.
> > >
> > > The appearance of the build log will change as follows:
> > >
> > > [Before]
> > >
> > >   $ make -C /path/to/my/linux M=/path/to/my/externel/module
> > >   make: Entering directory '/path/to/my/linux'
> > >     CC [M]  /path/to/my/externel/module/helloworld.o
> > >     MODPOST /path/to/my/externel/module/Module.symvers
> > >     CC [M]  /path/to/my/externel/module/helloworld.mod.o
> > >     CC [M]  /path/to/my/externel/module/.module-common.o
> > >     LD [M]  /path/to/my/externel/module/helloworld.ko
> > >   make: Leaving directory '/path/to/my/linux'
> > >
> > > [After]
> > >
> > >   $ make -C /path/to/my/linux M=/path/to/my/externel/module
> > >   make: Entering directory '/path/to/my/linux'
> > >   make[1]: Entering directory '/path/to/my/externel/module'
> > >     CC [M]  helloworld.o
> > >     MODPOST Module.symvers
> > >     CC [M]  helloworld.mod.o
> > >     CC [M]  .module-common.o
> > >     LD [M]  helloworld.ko
> > >   make[1]: Leaving directory '/path/to/my/externel/module'
> > >   make: Leaving directory '/path/to/my/linux'
> > >
> > > Printing "Entering directory" twice is cumbersome. This will be
> > > addressed later.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > > ---
> > >
> > > Changes in v2:
> > >  - Introduce a new 'srcroot' variable and clean-up code
> > >  - Reword Documentation/dev-tools/coccinelle.rst
> > >
> > >  Documentation/dev-tools/coccinelle.rst | 20 ++-----
> > >  Documentation/kbuild/makefiles.rst     | 14 +++++
> > >  Makefile                               | 80 +++++++++++++++-----------
> > >  rust/Makefile                          |  4 +-
> > >  scripts/Makefile.build                 |  2 +-
> > >  scripts/Makefile.clean                 |  2 +-
> > >  scripts/Makefile.compiler              |  2 +-
> > >  scripts/Makefile.modpost               |  6 +-
> > >  scripts/coccicheck                     |  6 +-
> > >  scripts/nsdeps                         |  8 +--
> > >  scripts/package/install-extmod-build   |  7 +++
> > >  11 files changed, 85 insertions(+), 66 deletions(-)
> > >
> > > diff --git a/Documentation/dev-tools/coccinelle.rst b/Documentation/dev-tools/coccinelle.rst
> > > index 535ce126fb4f..6e70a1e9a3c0 100644
> > > --- a/Documentation/dev-tools/coccinelle.rst
> > > +++ b/Documentation/dev-tools/coccinelle.rst
> > > @@ -250,25 +250,17 @@ variables for .cocciconfig is as follows:
> > >  - Your directory from which spatch is called is processed next
> > >  - The directory provided with the ``--dir`` option is processed last, if used
> > >
> > > -Since coccicheck runs through make, it naturally runs from the kernel
> > > -proper dir; as such the second rule above would be implied for picking up a
> > > -.cocciconfig when using ``make coccicheck``.
> > > -
> > >  ``make coccicheck`` also supports using M= targets. If you do not supply
> > >  any M= target, it is assumed you want to target the entire kernel.
> > >  The kernel coccicheck script has::
> > >
> > > -    if [ "$KBUILD_EXTMOD" = "" ] ; then
> > > -        OPTIONS="--dir $srctree $COCCIINCLUDE"
> > > -    else
> > > -        OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
> > > -    fi
> > > +    OPTIONS="--dir $srcroot $COCCIINCLUDE"
> > >
> > > -KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
> > > -the spatch ``--dir`` argument is used, as such third rule applies when whether
> > > -M= is used or not, and when M= is used the target directory can have its own
> > > -.cocciconfig file. When M= is not passed as an argument to coccicheck the
> > > -target directory is the same as the directory from where spatch was called.
> > > +Here, $srcroot refers to the source directory of the target: it points to the
> > > +external module's source directory when M= used, and otherwise, to the kernel
> > > +source directory. The third rule ensures the spatch reads the .cocciconfig from
> > > +the target directory, allowing external modules to have their own .cocciconfig
> > > +file.
> > >
> > >  If not using the kernel's coccicheck target, keep the above precedence
> > >  order logic of .cocciconfig reading. If using the kernel's coccicheck target,
> > > diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> > > index 7964e0c245ae..d36519f194dc 100644
> > > --- a/Documentation/kbuild/makefiles.rst
> > > +++ b/Documentation/kbuild/makefiles.rst
> > > @@ -449,6 +449,20 @@ $(obj)
> > >    to prerequisites are referenced with $(src) (because they are not
> > >    generated files).
> > >
> > > +$(srcroot)
> > > +  $(srcroot) refers to the root of the source you are building, which can be
> > > +  either the kernel source or the external modules source, depending on whether
> > > +  KBUILD_EXTMOD is set. This can be either a relative or an absolute path, but
> > > +  if KBUILD_ABS_SRCTREE=1 is set, it is always an absolute path.
> > > +
> > > +$(srctree)
> > > +  $(srctree) refers to the root of the kernel source tree. When building the
> > > +  kernel, this is the same as $(srcroot).
> > > +
> > > +$(objtree)
> > > +  $(objtree) refers to the root of the kernel object tree. It is ``.`` when
> > > +  building the kernel, but it is different when building external modules.
> > > +
> >
> > Thanks, I think it's nice that there is now such a clear definition.
> > $(srcroot) sounds fine to me.
> >
> > >  $(kecho)
> > >    echoing information to user in a rule is often a good practice
> > >    but when execution ``make -s`` one does not expect to see any output
> > > diff --git a/Makefile b/Makefile
> > > index cf1d55560ae2..e5f7ac7647a7 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -180,7 +180,24 @@ ifeq ("$(origin O)", "command line")
> > >    KBUILD_OUTPUT := $(O)
> > >  endif
> > >
> > > -output := $(KBUILD_OUTPUT)
> > > +ifdef KBUILD_EXTMOD
> > > +    ifdef KBUILD_OUTPUT
> > > +        objtree := $(realpath $(KBUILD_OUTPUT))
> > > +        $(if $(objtree),,$(error specified kernel directory "$(KBUILD_OUTPUT)" does not exist))
> > > +    else
> > > +        objtree := $(CURDIR)
> > > +    endif
> > > +    output := $(KBUILD_EXTMOD)
> > > +    # KBUILD_EXTMOD might be a relative path. Remember its absolute path before
> > > +    # Make changes the working directory.
> > > +    srcroot := $(realpath $(KBUILD_EXTMOD))
> > > +    $(if $(srcroot),,$(error specified external module directory "$(KBUILD_EXTMOD)" does not exist))
> > > +else
> > > +    objtree := .
> > > +    output := $(KBUILD_OUTPUT)
> > > +endif
> > > +
> > > +export objtree srcroot
> > >
> > >  # Do we want to change the working directory?
> > >  ifneq ($(output),)
> > > @@ -230,35 +247,33 @@ else # need-sub-make
> > >
> > >  # We process the rest of the Makefile if this is the final invocation of make
> > >
> > > -ifeq ($(abs_srctree),$(CURDIR))
> > > -        # building in the source tree
> > > -        srctree := .
> > > -     building_out_of_srctree :=
> > > +ifndef KBUILD_EXTMOD
> > > +srcroot := $(abs_srctree)
> > > +endif
> > > +
> > > +ifeq ($(srcroot),$(CURDIR))
> > > +building_out_of_srctree :=
> > >  else
> > > -        ifeq ($(abs_srctree)/,$(dir $(CURDIR)))
> > > -                # building in a subdirectory of the source tree
> > > -                srctree := ..
> > > -        else
> > > -                srctree := $(abs_srctree)
> > > -        endif
> > > -     building_out_of_srctree := 1
> > > +export building_out_of_srctree :=1

Nit: Adding a space between ':=1' for consistency?

> > >  endif
> > >
> > > -ifneq ($(KBUILD_ABS_SRCTREE),)
> > > -srctree := $(abs_srctree)
> > > +ifdef KBUILD_ABS_SRCTREE
> > > +    # Do not nothing. Use the absolute path.

Is this a superfluous "not"?

"Do nothing. Use the absolute path."?

> > > +else ifeq ($(srcroot),$(CURDIR))
> > > +    # Building in the source.
> > > +    srcroot := .
> > > +else ifeq ($(srcroot)/,$(dir $(CURDIR)))
> > > +    # Building in a subdirectory of the source.
> > > +    srcroot := ..
> > >  endif
> > >
> > > -objtree              := .
> > > +export srctree := $(if $(KBUILD_EXTMOD),$(abs_srctree),$(srcroot))
> >
> > With this patch applied, the following breaks for me:
> >
> >     $ make O=build M=fs/btrfs CONFIG_BTRFS_FS=m
> >     make[1]: Entering directory '/data/linux/kbuild-review/fs/btrfs'
> >       CC [M]  super.o
> >     In file included from <command-line>:
> >     /data/linux/kbuild-review/include/linux/compiler_types.h:89:10: fatal error: linux/compiler_attributes.h: No such file or directory
> >        89 | #include <linux/compiler_attributes.h>
> >           |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >     compilation terminated.
> >
> > Adding 'ccflags-y += -I$(srctree)/include' to fs/btrfs/Makefile breaks
> > the build loudly.  I could make it build again with
> >
> > diff --git a/Makefile b/Makefile
> > index e5f7ac7647a7b..3d95911f1a68f 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -555,7 +555,7 @@ USERINCLUDE    := \
> >  LINUXINCLUDE    := \
> >                 -I$(srctree)/arch/$(SRCARCH)/include \
> >                 -I$(objtree)/arch/$(SRCARCH)/include/generated \
> > -               $(if $(building_out_of_srctree),-I$(srctree)/include) \
> > +               $(if $(or $(building_out_of_srctree),$(filter $(srctree)/%, $(CURDIR))),-I$(srctree)/include) \
> >                 -I$(objtree)/include \
> >                 $(USERINCLUDE)
> >
> > but this does not feel good.  It building in-tree modules in this way a
> > valid thing to do?
> 
> Yes, it is a valid way.
> 
> This got broken with this commit, and fixed by the later commit,
> "kbuild: support building external modules in a separate build directory".
> 
> I will move the change for LINUXINCLUDE to this commit.

ah, thanks.  I should have seen that.

> > -VPATH		:=
> > -
> > -ifeq ($(KBUILD_EXTMOD),)
> >  ifdef building_out_of_srctree
> > -VPATH		:= $(srctree)
> > +export VPATH := $(srcroot)
> > +else
> > +VPATH :=
> >  endif
> > -endif
> > -
> > -export building_out_of_srctree srctree objtree VPATH
> >  
> >  # To make sure we do not include .config for any of the *config targets
> >  # catch them early, and hand them over to scripts/kconfig/Makefile
> > @@ -711,7 +726,7 @@ endif
> >  # in addition to whatever we do anyway.
> >  # Just "make" or "make all" shall build modules as well
> >  
> > -ifneq ($(filter all modules nsdeps %compile_commands.json clang-%,$(MAKECMDGOALS)),)
> > +ifneq ($(filter all modules nsdeps compile_commands.json clang-%,$(MAKECMDGOALS)),)
> >    KBUILD_MODULES := 1
> >  endif
> >  
> > @@ -1107,7 +1122,7 @@ export MODLIB
> >  
> >  PHONY += prepare0
> >  
> > -export extmod_prefix = $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)
> > +export extmod_prefix =
> >  export MODORDER := $(extmod_prefix)modules.order
> >  export MODULES_NSDEPS := $(extmod_prefix)modules.nsdeps
> >  
> > @@ -1799,14 +1814,10 @@ filechk_kernel.release = echo $(KERNELRELEASE)
> >  KBUILD_BUILTIN :=
> >  KBUILD_MODULES := 1
> >  
> > -build-dir := $(KBUILD_EXTMOD)
> > +build-dir := .
> >  
> > -compile_commands.json: $(extmod_prefix)compile_commands.json
> > -PHONY += compile_commands.json
> > -
> > -clean-dirs := $(KBUILD_EXTMOD)
> > -clean: private rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \
> > -	$(KBUILD_EXTMOD)/compile_commands.json
> > +clean-dirs := .
> > +clean: private rm-files := Module.symvers modules.nsdeps compile_commands.json
> >  
> >  PHONY += prepare
> >  # now expand this into a simple variable to reduce the cost of shell evaluations
> > @@ -1948,7 +1959,7 @@ $(clean-dirs):
> >  
> >  clean: $(clean-dirs)
> >  	$(call cmd,rmfiles)
> > -	@find $(or $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
> > +	@find . $(RCS_FIND_IGNORE) \
> >  		\( -name '*.[aios]' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
> >  		-o -name '*.ko.*' \
> >  		-o -name '*.dtb' -o -name '*.dtbo' \
> > @@ -1981,7 +1992,12 @@ tags TAGS cscope gtags: FORCE
> >  PHONY += rust-analyzer
> >  rust-analyzer:
> >  	+$(Q)$(CONFIG_SHELL) $(srctree)/scripts/rust_is_available.sh
> > +ifdef KBUILD_EXTMOD
> > +# FIXME: external modules must not descend into a sub-directory of the kernel
> > +	$(Q)$(MAKE) $(build)=$(objtree)/rust src=$(srctree)/rust $@
> > +else
> >  	$(Q)$(MAKE) $(build)=rust $@
> > +endif
> >  
> >  # Script to generate missing namespace dependencies
> >  # ---------------------------------------------------------------------------
> > diff --git a/rust/Makefile b/rust/Makefile
> > index b5e0a73b78f3..742740816c4b 100644
> > --- a/rust/Makefile
> > +++ b/rust/Makefile
> > @@ -362,8 +362,8 @@ rust-analyzer:
> >  	$(Q)$(srctree)/scripts/generate_rust_analyzer.py \
> >  		--cfgs='core=$(core-cfgs)' --cfgs='alloc=$(alloc-cfgs)' \
> >  		$(realpath $(srctree)) $(realpath $(objtree)) \
> > -		$(rustc_sysroot) $(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
> > -		$(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
> > +		$(rustc_sysroot) $(RUST_LIB_SRC) $(if $(KBUILD_EXTMOD),$(srcroot)) \
> > +		> rust-project.json
> >  
> >  redirect-intrinsics = \
> >  	__addsf3 __eqsf2 __extendsfdf2 __gesf2 __lesf2 __ltsf2 __mulsf3 __nesf2 __truncdfsf2 __unordsf2 \
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index 64cd046f8fd8..1aa928a6fb4f 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -3,7 +3,7 @@
> >  # Building
> >  # ==========================================================================
> >  
> > -src := $(if $(VPATH),$(VPATH)/)$(obj)
> > +src := $(srcroot)/$(obj)
> >  
> >  PHONY := $(obj)/
> >  $(obj)/:
> > diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
> > index 4fcfab40ed61..6ead00ec7313 100644
> > --- a/scripts/Makefile.clean
> > +++ b/scripts/Makefile.clean
> > @@ -3,7 +3,7 @@
> >  # Cleaning up
> >  # ==========================================================================
> >  
> > -src := $(if $(VPATH),$(VPATH)/)$(obj)
> > +src := $(srcroot)/$(obj)
> >  
> >  PHONY := __clean
> >  __clean:
> > diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> > index e0842496d26e..8c1029687e2e 100644
> > --- a/scripts/Makefile.compiler
> > +++ b/scripts/Makefile.compiler
> > @@ -13,7 +13,7 @@ cc-cross-prefix = $(firstword $(foreach c, $(1), \
> >  			$(if $(shell command -v -- $(c)gcc 2>/dev/null), $(c))))
> >  
> >  # output directory for tests below
> > -TMPOUT = $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_$$$$
> > +TMPOUT = .tmp_$$$$
> >  
> >  # try-run
> >  # Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
> > diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> > index 12e7c15d099c..78d2ca4f25f5 100644
> > --- a/scripts/Makefile.modpost
> > +++ b/scripts/Makefile.modpost
> > @@ -111,13 +111,13 @@ endif
> >  else
> >  
> >  # set src + obj - they may be used in the modules's Makefile
> > -obj := $(KBUILD_EXTMOD)
> > -src := $(if $(VPATH),$(VPATH)/)$(obj)
> > +obj := .
> > +src := $(srcroot)
> >  
> >  # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
> >  include $(kbuild-file)
> >  
> > -output-symdump := $(KBUILD_EXTMOD)/Module.symvers
> > +output-symdump := Module.symvers
> >  
> >  ifeq ($(wildcard $(objtree)/Module.symvers),)
> >  missing-input := $(objtree)/Module.symvers
> > diff --git a/scripts/coccicheck b/scripts/coccicheck
> > index e52cb43fede6..0e6bc5a10320 100755
> > --- a/scripts/coccicheck
> > +++ b/scripts/coccicheck
> > @@ -80,11 +80,7 @@ command results in a shift count error.'
> >      NPROC=1
> >  else
> >      ONLINE=0
> > -    if [ "$KBUILD_EXTMOD" = "" ] ; then
> > -        OPTIONS="--dir $srctree $COCCIINCLUDE"
> > -    else
> > -        OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
> > -    fi
> > +    OPTIONS="--dir $srcroot $COCCIINCLUDE"
> >  
> >      # Use only one thread per core by default if hyperthreading is enabled
> >      THREADS_PER_CORE=$(LANG=C lscpu | grep "Thread(s) per core: " | tr -cd "[:digit:]")
> > diff --git a/scripts/nsdeps b/scripts/nsdeps
> > index f1718cc0d700..8ca12e2b5c03 100644
> > --- a/scripts/nsdeps
> > +++ b/scripts/nsdeps
> > @@ -19,12 +19,6 @@ if ! { echo "$SPATCH_REQ_VERSION"; echo "$SPATCH_VERSION"; } | sort -CV ; then
> >  	exit 1
> >  fi
> >  
> > -if [ "$KBUILD_EXTMOD" ]; then
> > -	src_prefix=
> > -else
> > -	src_prefix=$srctree/
> > -fi
> > -
> >  generate_deps_for_ns() {
> >  	$SPATCH --very-quiet --in-place --sp-file \
> >  		$srctree/scripts/coccinelle/misc/add_namespace.cocci -D nsdeps -D ns=$1 $2
> > @@ -34,7 +28,7 @@ generate_deps() {
> >  	local mod=${1%.ko:}
> >  	shift
> >  	local namespaces="$*"
> > -	local mod_source_files=$(sed "s|^\(.*\)\.o$|${src_prefix}\1.c|" $mod.mod)
> > +	local mod_source_files=$(sed "s|^\(.*\)\.o$|${srcroot}/\1.c|" $mod.mod)
> >  
> >  	for ns in $namespaces; do
> >  		echo "Adding namespace $ns to module $mod.ko."
> > diff --git a/scripts/package/install-extmod-build b/scripts/package/install-extmod-build
> > index 7ec1f061a519..64d958ee45f3 100755
> > --- a/scripts/package/install-extmod-build
> > +++ b/scripts/package/install-extmod-build
> > @@ -51,6 +51,13 @@ mkdir -p "${destdir}"
> >  if [ "${CC}" != "${HOSTCC}" ]; then
> >  	echo "Rebuilding host programs with ${CC}..."
> >  
> > +	# This leverages external module building.
> > +	# - Clear sub_make_done to allow the top-level Makefile to redo sub-make.
> > +	# - Filter out --no-print-directory to print "Entering directory" logs
> > +	#   when Make changes the working directory.
> > +	unset sub_make_done
> > +	MAKEFLAGS=$(echo "${MAKEFLAGS}" | sed s/--no-print-directory//)
> > +
> >  	cat <<-'EOF' >  "${destdir}/Kbuild"
> >  	subdir-y := scripts
> >  	EOF
> > -- 
> > 2.43.0


Thanks, again!

Reviewed-by: Nicolas Schier <n.schier@....de>

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