kbuild: use $(obj)/ instead of $(src)/ for common pattern rules

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

  src := $(obj)

Before changing the semantics of $(src) in the next commit, this commit
replaces $(obj)/ with $(src)/ in pattern rules where the prerequisite
might be a generated file.

C, assembly, Rust, and DTS files are sometimes generated by tools, so
they could be either generated files or real sources. The $(obj)/ prefix
works for both cases with the help of VPATH.

As mentioned above, $(obj) and $(src) are the same at this point, hence
this commit has no functional change.

I did not modify scripts/Makefile.userprogs because there is no use
case where userspace C files are generated.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

scripts/Makefile.build

@@ -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: $(src)/%.c FORCE
+$(obj)/%.s: $(obj)/%.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: $(src)/%.c FORCE
+$(obj)/%.i: $(obj)/%.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 : $(src)/%.c FORCE
+$(obj)/%.symtypes : $(obj)/%.c FORCE
 	$(call cmd,cc_symtypes_c)
 
 # LLVM assembly
@@ -141,7 +141,7 @@ $(obj)/%.symtypes : $(src)/%.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: $(src)/%.c FORCE
+$(obj)/%.ll: $(obj)/%.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: $(src)/%.c $(recordmcount_source) FORCE
+$(obj)/%.o: $(obj)/%.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: $(src)/%.c FORCE
+$(obj)/%.lst: $(obj)/%.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: $(src)/%.rs FORCE
+$(obj)/%.o: $(obj)/%.rs FORCE
 	+$(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: $(src)/%.rs FORCE
+$(obj)/%.rsi: $(obj)/%.rs FORCE
 	+$(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: $(src)/%.rs FORCE
+$(obj)/%.s: $(obj)/%.rs FORCE
 	+$(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: $(src)/%.rs FORCE
+$(obj)/%.ll: $(obj)/%.rs FORCE
 	+$(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 : $(src)/%.S FORCE
+$(obj)/%.symtypes : $(obj)/%.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: $(src)/%.S FORCE
+$(obj)/%.s: $(obj)/%.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: $(src)/%.S FORCE
+$(obj)/%.o: $(obj)/%.S FORCE
 	$(call if_changed_rule,as_o_S)
 
 targets += $(filter-out $(subdir-builtin), $(real-obj-y))

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)/%: $(src)/%.c FORCE
+$(host-csingle): $(obj)/%: $(obj)/%.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: $(src)/%.c FORCE
+$(host-cobjs): $(obj)/%.o: $(obj)/%.c FORCE
 	$(call if_changed_dep,host-cobjs)
 
 # Link an executable based on list of .o files, a mixture of .c and .cc

scripts/Makefile.lib

@@ -423,7 +423,7 @@ quiet_cmd_dtb = $(quiet_cmd_dtc)
       cmd_dtb = $(cmd_dtc)
 endif
 
-$(obj)/%.dtb: $(src)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
+$(obj)/%.dtb: $(obj)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
 	$(call if_changed_dep,dtb)
 
 $(obj)/%.dtbo: $(src)/%.dtso $(DTC) FORCE