[PATCH] kbuild: Support separating source and output of the external module

From: Jing Leng
Date: Wed Sep 11 2024 - 07:20:54 EST

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Revert commit "9a0ebe5011f4", originally when compiling external modules,
the compiled output can be separated from the source code with the
following command:
make -C <kernel_src> O=<kernel_out> src=<module_src> M=<module_out>
It is used to https://github.com/lengjingzju/cbuild-ng (inc.mod.mk).

But "src" is an internal variable, so this patch adds a variable "S"
which is specifically used to change the default value of "src".

Fixes: 9a0ebe5011f4 ("kbuild: use $(obj)/ instead of $(src)/ for common pattern rules")
Signed-off-by: Jing Leng <3090101217@xxxxxxxxxx>
---
Documentation/kbuild/modules.rst | 45 +++++++++++++++++++++++---------
scripts/Makefile.build | 28 ++++++++++----------
scripts/Makefile.clean | 2 +-
scripts/Makefile.host | 6 ++---
scripts/Makefile.lib | 2 +-
scripts/Makefile.modpost | 2 +-
6 files changed, 52 insertions(+), 33 deletions(-)

diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
index 131863142cbb..1c4d3810b1dd 100644
--- a/Documentation/kbuild/modules.rst
+++ b/Documentation/kbuild/modules.rst
@@ -72,14 +72,23 @@ executed to make module versioning work.
2.1 Command Syntax
==================

- The command to build an external module is::
+ The full command to build an external module is::

- $ make -C <path_to_kernel_src> M=$PWD
+ $ make -C <kernel_src> O=<kernel_out> S=<module_src> M=<module_out>

- The kbuild system knows that an external module is being built
- due to the "M=<dir>" option given in the command.
+ If <kernel_out> is the same as <kernel_src>, "O=" can be omitted::

- To build against the running kernel use::
+ $ make -C <kernel_src> S=<module_src> M=<module_out>
+
+ If <module_out> is the same as <module_src>, "S=" can be omitted::
+
+ $ make -C <kernel_src> O=<kernel_out> M=<module_src>
+
+ If both of the above are satisfied, the command is::
+
+ $ make -C <kernel_src> M=<module_src>
+
+ So to build against the running kernel can use::

$ make -C /lib/modules/`uname -r`/build M=$PWD

@@ -91,20 +100,29 @@ executed to make module versioning work.
2.2 Options
===========

- ($KDIR refers to the path of the kernel source directory.)
-
- make -C $KDIR M=$PWD
+ make -C <kernel_src> O=<kernel_out> S=<module_src> M=<module_out>

- -C $KDIR
+ -C <kernel_src>
The directory where the kernel source is located.
"make" will actually change to the specified directory
when executing and will change back when finished.

- M=$PWD
+ O=<kernel_out>
+ The value given to "O" is the absolute path of the
+ directory where the kernel output (.config file) is located.
+ If <kernel_out> is the same as <kernel_src>,
+ "O=<kernel_out>" can be omitted.
+
+ S=<module_src>
+ The value given to "S" is the absolute path of the
+ directory where the external module source (kbuild file)
+ is located. If <module_out> is the same as <module_src>,
+ "S=<module_src>" can be omitted.
+
+ M=<module_out>
Informs kbuild that an external module is being built.
The value given to "M" is the absolute path of the
- directory where the external module (kbuild file) is
- located.
+ directory where the external module output is located.

2.3 Targets
===========
@@ -112,7 +130,7 @@ executed to make module versioning work.
When building an external module, only a subset of the "make"
targets are available.

- make -C $KDIR M=$PWD [target]
+ make -C <kernel_src> O=<kernel_out> S=<module_src> M=<module_out> [target]

The default will build the module(s) located in the current
directory, so a target does not need to be specified. All
@@ -151,6 +169,7 @@ executed to make module versioning work.
make -C $KDIR M=$PWD foo.ko
make -C $KDIR M=$PWD ./

+ ($KDIR refers to the path of the kernel source directory.)

3. Creating a Kbuild File for an External Module
================================================
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a5ac8ed1936f..44b38cdb76df 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -3,7 +3,7 @@
# Building
# ==========================================================================

-src := $(if $(VPATH),$(VPATH)/)$(obj)
+src := $(if $(S),$(S),$(if $(VPATH),$(VPATH)/)$(obj))

PHONY := $(obj)/
$(obj)/:
@@ -113,13 +113,13 @@ endif
quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS) $(CC_FLAGS_LTO), $(c_flags)) -fverbose-asm -S -o $@ $<

-$(obj)/%.s: $(obj)/%.c FORCE
+$(obj)/%.s: $(src)/%.c FORCE
$(call if_changed_dep,cc_s_c)

quiet_cmd_cpp_i_c = CPP $(quiet_modtag) $@
cmd_cpp_i_c = $(CPP) $(c_flags) -o $@ $<

-$(obj)/%.i: $(obj)/%.c FORCE
+$(obj)/%.i: $(src)/%.c FORCE
$(call if_changed_dep,cpp_i_c)

genksyms = scripts/genksyms/genksyms \
@@ -133,7 +133,7 @@ cmd_gensymtypes_c = $(CPP) -D__GENKSYMS__ $(c_flags) $< | $(genksyms)
quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
cmd_cc_symtypes_c = $(call cmd_gensymtypes_c,true,$@) >/dev/null

-$(obj)/%.symtypes : $(obj)/%.c FORCE
+$(obj)/%.symtypes : $(src)/%.c FORCE
$(call cmd,cc_symtypes_c)

# LLVM assembly
@@ -141,7 +141,7 @@ $(obj)/%.symtypes : $(obj)/%.c FORCE
quiet_cmd_cc_ll_c = CC $(quiet_modtag) $@
cmd_cc_ll_c = $(CC) $(c_flags) -emit-llvm -S -fno-discard-value-names -o $@ $<

-$(obj)/%.ll: $(obj)/%.c FORCE
+$(obj)/%.ll: $(src)/%.c FORCE
$(call if_changed_dep,cc_ll_c)

# C (.c) files
@@ -240,7 +240,7 @@ define rule_as_o_S
endef

# Built-in and composite module parts
-$(obj)/%.o: $(obj)/%.c $(recordmcount_source) FORCE
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
$(call if_changed_rule,cc_o_c)
$(call cmd,force_checksrc)

@@ -257,7 +257,7 @@ quiet_cmd_cc_lst_c = MKLST $@
$(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
System.map $(OBJDUMP) > $@

-$(obj)/%.lst: $(obj)/%.c FORCE
+$(obj)/%.lst: $(src)/%.c FORCE
$(call if_changed_dep,cc_lst_c)

# Compile Rust sources (.rs)
@@ -290,7 +290,7 @@ rust_common_cmd = \
quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
cmd_rustc_o_rs = $(rust_common_cmd) --emit=obj=$@ $<

-$(obj)/%.o: $(obj)/%.rs FORCE
+$(obj)/%.o: $(src)/%.rs FORCE
+$(call if_changed_dep,rustc_o_rs)

quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
@@ -298,19 +298,19 @@ quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@

-$(obj)/%.rsi: $(obj)/%.rs FORCE
+$(obj)/%.rsi: $(src)/%.rs FORCE
+$(call if_changed_dep,rustc_rsi_rs)

quiet_cmd_rustc_s_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
cmd_rustc_s_rs = $(rust_common_cmd) --emit=asm=$@ $<

-$(obj)/%.s: $(obj)/%.rs FORCE
+$(obj)/%.s: $(src)/%.rs FORCE
+$(call if_changed_dep,rustc_s_rs)

quiet_cmd_rustc_ll_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
cmd_rustc_ll_rs = $(rust_common_cmd) --emit=llvm-ir=$@ $<

-$(obj)/%.ll: $(obj)/%.rs FORCE
+$(obj)/%.ll: $(src)/%.rs FORCE
+$(call if_changed_dep,rustc_ll_rs)

# Compile assembler sources (.S)
@@ -336,14 +336,14 @@ cmd_gensymtypes_S = \
quiet_cmd_cc_symtypes_S = SYM $(quiet_modtag) $@
cmd_cc_symtypes_S = $(call cmd_gensymtypes_S,true,$@) >/dev/null

-$(obj)/%.symtypes : $(obj)/%.S FORCE
+$(obj)/%.symtypes : $(src)/%.S FORCE
$(call cmd,cc_symtypes_S)

quiet_cmd_cpp_s_S = CPP $(quiet_modtag) $@
cmd_cpp_s_S = $(CPP) $(a_flags) -o $@ $<

-$(obj)/%.s: $(obj)/%.S FORCE
+$(obj)/%.s: $(src)/%.S FORCE
$(call if_changed_dep,cpp_s_S)

quiet_cmd_as_o_S = AS $(quiet_modtag) $@
@@ -358,7 +358,7 @@ cmd_gen_symversions_S = $(call gen_symversions,S)

endif

-$(obj)/%.o: $(obj)/%.S FORCE
+$(obj)/%.o: $(src)/%.S FORCE
$(call if_changed_rule,as_o_S)

targets += $(filter-out $(subdir-builtin), $(real-obj-y))
diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
index 4fcfab40ed61..6ce7514aefc8 100644
--- a/scripts/Makefile.clean
+++ b/scripts/Makefile.clean
@@ -3,7 +3,7 @@
# Cleaning up
# ==========================================================================

-src := $(if $(VPATH),$(VPATH)/)$(obj)
+src := $(if $(S),$(S),$(if $(VPATH),$(VPATH)/)$(obj))

PHONY := __clean
__clean:
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index e85be7721a48..3c17e6ba421c 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -112,7 +112,7 @@ endif
quiet_cmd_host-csingle = HOSTCC $@
cmd_host-csingle = $(HOSTCC) $(hostc_flags) $(KBUILD_HOSTLDFLAGS) -o $@ $< \
$(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(target-stem))
-$(host-csingle): $(obj)/%: $(obj)/%.c FORCE
+$(host-csingle): $(obj)/%: $(src)/%.c FORCE
$(call if_changed_dep,host-csingle)

# Link an executable based on list of .o files, all plain c
@@ -129,7 +129,7 @@ $(call multi_depend, $(host-cmulti), , -objs)
# host-cobjs -> .o
quiet_cmd_host-cobjs = HOSTCC $@
cmd_host-cobjs = $(HOSTCC) $(hostc_flags) -c -o $@ $<
-$(host-cobjs): $(obj)/%.o: $(obj)/%.c FORCE
+$(host-cobjs): $(obj)/%.o: $(src)/%.c FORCE
$(call if_changed_dep,host-cobjs)

# Link an executable based on list of .o files, a mixture of .c and .cc
@@ -146,7 +146,7 @@ $(call multi_depend, $(host-cxxmulti), , -objs -cxxobjs)
# Create .o file from a single .cc (C++) file
quiet_cmd_host-cxxobjs = HOSTCXX $@
cmd_host-cxxobjs = $(HOSTCXX) $(hostcxx_flags) -c -o $@ $<
-$(host-cxxobjs): $(obj)/%.o: $(obj)/%.cc FORCE
+$(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
$(call if_changed_dep,host-cxxobjs)

# Create executable from a single Rust crate (which may consist of
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 207325eaf1d1..6f961aa5790d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -430,7 +430,7 @@ DT_TMP_SCHEMA := $(objtree)/$(DT_BINDING_DIR)/processed-schema.json
dtb-check-enabled = $(if $(filter %.dtb, $@),y)
endif

-$(obj)/%.dtb: $(obj)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
+$(obj)/%.dtb: $(src)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
$(call if_changed_dep,dtc)

$(obj)/%.dtbo: $(src)/%.dtso $(DTC) FORCE
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 44936ebad161..12afe2acbe05 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -112,7 +112,7 @@ else

# set src + obj - they may be used in the modules's Makefile
obj := $(KBUILD_EXTMOD)
-src := $(if $(VPATH),$(VPATH)/)$(obj)
+src := $(if $(S),$(S),$(if $(VPATH),$(VPATH)/)$(obj))

# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
include $(kbuild-file)
--
2.25.1

Next message: Sourabh Jain: "[PATCH RESEND v2] kexec/crash: no crash update when kexec in progress"
Previous message: Muhammad Usama Anjum: "[PATCH] ASoc: mediatek: mt8365: Print the ret value"
Next in thread: Masahiro Yamada: "Re: [PATCH] kbuild: Support separating source and output of the external module"
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