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.
This change has caused O=<relative directory> to fail.
For example:
make O=build defconfig
make -j$(nproc) V=1 O=build bindeb-pkg
outputs:
make ARCH=x86 KERNELRELEASE=6.13.0-rc1 KBUILD_BUILD_VERSION=3 run-command KBUILD_RUN_COMMAND='+$(srctree)/scripts/package/builddeb linux-libc-dev'
dh_installchangelogs -plinux-image-6.13.0-rc1
../scripts/package/builddeb linux-headers-6.13.0-rc1
dh_compress -plinux-image-6.13.0-rc1
dh_fixperms -plinux-image-6.13.0-rc1
dh_gencontrol -plinux-image-6.13.0-rc1 -- -fdebian/image.files
Rebuilding host programs with x86_64-linux-gnu-gcc...
make[6]: Entering directory '/scratch/kernels/linux/build'
/scratch/kernels/linux/Makefile:190: *** specified kernel directory "build" does not exist. Stop.
It is stepping into this directory and then trying to find the directory
it just stepped into so $(realpath $(KBUILD_OUTPUT)) returns an empty
string.
Using an absolute directory resolves this problem, but I believe it
shouldn't be necessary.
- Charlie
>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
> Changes in v2:
> - Introduce a new 'srcroot' variable and clean-up code
> - Reword Documentation/dev-tools/coccinelle.rst
>
> Documentation/dev-tools/coccinelle.rst | 20 ++-----
> Documentation/kbuild/makefiles.rst | 14 +++++
> Makefile | 80 +++++++++++++++-----------
> rust/Makefile | 4 +-
> scripts/Makefile.build | 2 +-
> scripts/Makefile.clean | 2 +-
> scripts/Makefile.compiler | 2 +-
> scripts/Makefile.modpost | 6 +-
> scripts/coccicheck | 6 +-
> scripts/nsdeps | 8 +--
> scripts/package/install-extmod-build | 7 +++
> 11 files changed, 85 insertions(+), 66 deletions(-)
>
> diff --git a/Documentation/dev-tools/coccinelle.rst b/Documentation/dev-tools/coccinelle.rst
> index 535ce126fb4f..6e70a1e9a3c0 100644
> --- a/Documentation/dev-tools/coccinelle.rst
> +++ b/Documentation/dev-tools/coccinelle.rst
> @@ -250,25 +250,17 @@ variables for .cocciconfig is as follows:
> - Your directory from which spatch is called is processed next
> - The directory provided with the ``--dir`` option is processed last, if used
>
> -Since coccicheck runs through make, it naturally runs from the kernel
> -proper dir; as such the second rule above would be implied for picking up a
> -.cocciconfig when using ``make coccicheck``.
> -
> ``make coccicheck`` also supports using M= targets. If you do not supply
> any M= target, it is assumed you want to target the entire kernel.
> The kernel coccicheck script has::
>
> - if [ "$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.
> +
> $(kecho)
> echoing information to user in a rule is often a good practice
> but when execution ``make -s`` one does not expect to see any output
> diff --git a/Makefile b/Makefile
> index cf1d55560ae2..e5f7ac7647a7 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -180,7 +180,24 @@ ifeq ("$(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 := $(abs_srctree)
> - endif
> - building_out_of_srctree := 1
> +export building_out_of_srctree :=1
> endif
>
> -ifneq ($(KBUILD_ABS_SRCTREE),)
> -srctree := $(abs_srctree)
> +ifdef KBUILD_ABS_SRCTREE
> + # Do not nothing. Use the absolute path.
> +else ifeq ($(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),$(srcroot))
>
> -VPATH :=
> -
> -ifeq ($(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
