kbuild: Generate *.lds instead of *.lds.s

When building a kernel on platforms where the filesytem do
not distingush between upper and lower case the rule:
.S -> .s did not work.
In a normal build this is only used for linker scripts.
So create a separate rule for .lds files, and use generic cpp flags.

Patch from: Dan Aloni <da-x@colinux.org>
Modified to use cpp flags + added documentation.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Documentation/kbuild/makefiles.txt

@@ -938,6 +938,37 @@ When kbuild executes the following steps are followed (roughly):
 	will be displayed with "make KBUILD_VERBOSE=0".
 	
 
+--- 6.8 Preprocessing linker scripts
+
+	When the vmlinux image is build the linker script:
+	arch/$(ARCH)/kernel/vmlinux.lds is used.
+	The script is a preprocessed variant of the file vmlinux.lds.S
+	located in the same directory.
+	kbuild knows .lds file and includes a rule *lds.S -> *lds.
+	
+	Example:
+		#arch/i386/kernel/Makefile
+		always := vmlinux.lds
+	
+		#Makefile
+		export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
+		
+	The assigment to $(always) is used to tell kbuild to build the
+	target: vmlinux.lds.
+	The assignment to $(CPPFLAGS_vmlinux.lds) tell kbuild to use the
+	specified options when building the target vmlinux.lds.
+	
+	When building the *.lds target kbuild used the variakles:
+	CPPFLAGS	: Set in top-level Makefile
+	EXTRA_CPPFLAGS	: May be set in the kbuild makefile
+	CPPFLAGS_$(@F)  : Target specific flags.
+	                  Note that the full filename is used in this
+	                  assignment.
+
+	The kbuild infrastructure for *lds file are used in several
+	architecture specific files.
+
+
 === 7 Kbuild Variables
 
 The top Makefile exports the following variables:

Makefile

@@ -545,7 +545,7 @@ endef
 quiet_cmd_sysmap = SYSMAP 
       cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap
 		   
-LDFLAGS_vmlinux += -T arch/$(ARCH)/kernel/vmlinux.lds.s
+LDFLAGS_vmlinux += -T arch/$(ARCH)/kernel/vmlinux.lds
 
 #	Generate section listing all symbols and add it into vmlinux
 #	It's a three stage process:
@@ -591,13 +591,13 @@ cmd_kallsyms = $(NM) -n $< | $(KALLSYMS) $(foreach x,$(CONFIG_KALLSYMS_ALL),--al
 .tmp_kallsyms%.S: .tmp_vmlinux% $(KALLSYMS)
 	$(call cmd,kallsyms)
 
-.tmp_vmlinux1: $(vmlinux-objs) arch/$(ARCH)/kernel/vmlinux.lds.s FORCE
+.tmp_vmlinux1: $(vmlinux-objs) arch/$(ARCH)/kernel/vmlinux.lds FORCE
 	$(call if_changed_rule,vmlinux__)
 
-.tmp_vmlinux2: $(vmlinux-objs) .tmp_kallsyms1.o arch/$(ARCH)/kernel/vmlinux.lds.s FORCE
+.tmp_vmlinux2: $(vmlinux-objs) .tmp_kallsyms1.o arch/$(ARCH)/kernel/vmlinux.lds FORCE
 	$(call if_changed_rule,vmlinux__)
 
-.tmp_vmlinux3: $(vmlinux-objs) .tmp_kallsyms2.o arch/$(ARCH)/kernel/vmlinux.lds.s FORCE
+.tmp_vmlinux3: $(vmlinux-objs) .tmp_kallsyms2.o arch/$(ARCH)/kernel/vmlinux.lds FORCE
 	$(call if_changed_rule,vmlinux__)
 
 endif
@@ -618,13 +618,13 @@ define rule_vmlinux
 	$(rule_verify_kallsyms)
 endef
 
-vmlinux: $(vmlinux-objs) $(kallsyms.o) arch/$(ARCH)/kernel/vmlinux.lds.s FORCE
+vmlinux: $(vmlinux-objs) $(kallsyms.o) arch/$(ARCH)/kernel/vmlinux.lds FORCE
 	$(call if_changed_rule,vmlinux)
 
 #	The actual objects are generated when descending, 
 #	make sure no implicit rule kicks in
 
-$(sort $(vmlinux-objs)) arch/$(ARCH)/kernel/vmlinux.lds.s: $(vmlinux-dirs) ;
+$(sort $(vmlinux-objs)) arch/$(ARCH)/kernel/vmlinux.lds: $(vmlinux-dirs) ;
 
 # Handle descending into subdirectories listed in $(vmlinux-dirs)
 # Preset locale variables to speed up the build process. Limit locale
@@ -687,7 +687,7 @@ prepare-all: prepare0 prepare
 #	Leave this as default for preprocessing vmlinux.lds.S, which is now
 #	done in arch/$(ARCH)/kernel/Makefile
 
-export AFLAGS_vmlinux.lds.o += -P -C -U$(ARCH)
+export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
 
 # Single targets
 # ---------------------------------------------------------------------------

arch/i386/kernel/Makefile

@@ -2,7 +2,7 @@
 # Makefile for the linux kernel.
 #
 
-extra-y := head.o init_task.o vmlinux.lds.s
+extra-y := head.o init_task.o vmlinux.lds
 
 obj-y	:= process.o semaphore.o signal.o entry.o traps.o irq.o vm86.o \
 		ptrace.o i8259.o ioport.o ldt.o setup.o time.o sys_i386.o \

scripts/Makefile.build

@@ -219,6 +219,14 @@ cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<
 targets += $(real-objs-y) $(real-objs-m) $(lib-y)
 targets += $(extra-y) $(MAKECMDGOALS) $(always)
 
+# Linker scripts preprocessor (.lds.S -> .lds)
+# ---------------------------------------------------------------------------
+quiet_cmd_cpp_lds_S = LDS     $@
+      cmd_cpp_lds_S = $(CPP) $(cpp_flags) -D__ASSEMBLY__ -o $@ $<
+
+%.lds: %.lds.S FORCE
+	$(call if_changed_dep,cpp_lds_S)
+
 # Build the compiled-in targets
 # ---------------------------------------------------------------------------
 

scripts/Makefile.lib

@@ -100,6 +100,7 @@ modname_flags  = $(if $(filter 1,$(words $(modname))),-DKBUILD_MODNAME=$(subst $
 
 _c_flags       = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o)
 _a_flags       = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
+_cpp_flags     = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))
 
 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
@@ -107,6 +108,7 @@ _a_flags       = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
 ifeq ($(KBUILD_SRC),)
 __c_flags	= $(_c_flags)
 __a_flags	= $(_a_flags)
+__cpp_flags     = $(_cpp_flags)
 else
 
 # Prefix -I with $(srctree) if it is not an absolute path
@@ -120,6 +122,7 @@ flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))
 # FIXME: Replace both with specific CFLAGS* statements in the makefiles
 __c_flags	= $(call addtree,-I$(obj)) $(call flags,_c_flags)
 __a_flags	=                          $(call flags,_a_flags)
+__cpp_flags     =                          $(call flags,_cpp_flags)
 endif
 
 c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
@@ -129,6 +132,8 @@ c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
 a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
 		 $(__a_flags) $(modkern_aflags)
 
+cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)
+
 ld_flags       = $(LDFLAGS) $(EXTRA_LDFLAGS)
 
 # Finds the multi-part object the current object will be linked into