kbuild: asm-generic support

There is an increasing amount of header files
shared between individual architectures in asm-generic.
To avoid a lot of dummy wrapper files that just
include the corresponding file in asm-generic provide
some basic support in kbuild for this.

With the following patch an architecture can maintain
a list of files in the file arch/$(ARCH)/include/asm/Kbuild

To use a generic file just add:

        generic-y += <name-of-header-file.h>

For each file listed kbuild will generate the necessary
wrapper in arch/$(ARCH)/include/generated/asm.

When installing userspace headers a wrapper is likewise created.

The original inspiration for this came from the unicore32
patchset - although a different method is used.

The patch includes several improvements from Arnd Bergmann.
Michael Marek contributed Makefile.asm-generic.

Remis Baima did an intial implementation along to achive
the same - see https://patchwork.kernel.org/patch/13352/

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Guan Xuetao <guanxuetao@mprc.pku.edu.cn>
Tested-by: Guan Xuetao <guanxuetao@mprc.pku.edu.cn>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Remis Lima Baima <remis.developer@googlemail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

.gitignore

@@ -57,6 +57,7 @@ modules.builtin
 include/config
 include/linux/version.h
 include/generated
+arch/*/include/generated
 
 # stgit generated dirs
 patches-*

Documentation/kbuild/makefiles.txt

@@ -40,11 +40,13 @@ This document describes the Linux kernel Makefiles.
 	   --- 6.6 Commands useful for building a boot image
 	   --- 6.7 Custom kbuild commands
 	   --- 6.8 Preprocessing linker scripts
+	   --- 6.9 Generic header files
 
 	=== 7 Kbuild syntax for exported headers
 		--- 7.1 header-y
 		--- 7.2 objhdr-y
 		--- 7.3 destination-y
+		--- 7.4 generic-y
 
 	=== 8 Kbuild Variables
 	=== 9 Makefile language
@@ -1214,6 +1216,14 @@ When kbuild executes, the following steps are followed (roughly):
 	The kbuild infrastructure for *lds file are used in several
 	architecture-specific files.
 
+--- 6.9 Generic header files
+
+	The directory include/asm-generic contains the header files
+	that may be shared between individual architectures.
+	The recommended approach how to use a generic header file is
+	to list the file in the Kbuild file.
+	See "7.4 generic-y" for further info on syntax etc.
+
 === 7 Kbuild syntax for exported headers
 
 The kernel include a set of headers that is exported to userspace.
@@ -1270,6 +1280,32 @@ See subsequent chapter for the syntax of the Kbuild file.
 	In the example above all exported headers in the Kbuild file
 	will be located in the directory "include/linux" when exported.
 
+	--- 7.4 generic-y
+
+	If an architecture uses a verbatim copy of a header from
+	include/asm-generic then this is listed in the file
+	arch/$(ARCH)/include/asm/Kbuild like this:
+
+		Example:
+			#arch/x86/include/asm/Kbuild
+			generic-y += termios.h
+			generic-y += rtc.h
+
+	During the prepare phase of the build a wrapper include
+	file is generated in the directory:
+
+		arch/$(ARCH)/include/generated/asm
+
+	When a header is exported where the architecture uses
+	the generic header a similar wrapper is generated as part
+	of the set of exported headers in the directory:
+
+		usr/include/asm
+
+	The generated wrapper will in both cases look like the following:
+
+		Example: termios.h
+			#include <asm-generic/termios.h>
 
 === 8 Kbuild Variables
 

Makefile

@@ -349,7 +349,8 @@ CFLAGS_GCOV	= -fprofile-arcs -ftest-coverage
 
 # Use LINUXINCLUDE when you must reference the include/ directory.
 # Needed to be compatible with the O= option
-LINUXINCLUDE    := -I$(srctree)/arch/$(hdr-arch)/include -Iinclude \
+LINUXINCLUDE    := -I$(srctree)/arch/$(hdr-arch)/include \
+                   -Iarch/$(hdr-arch)/include/generated -Iinclude \
                    $(if $(KBUILD_SRC), -I$(srctree)/include) \
                    -include include/generated/autoconf.h
 
@@ -417,6 +418,12 @@ ifneq ($(KBUILD_SRC),)
 	    $(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
 endif
 
+# Support for using generic headers in asm-generic
+PHONY += asm-generic
+asm-generic:
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.asm-generic \
+	            obj=arch/$(SRCARCH)/include/generated/asm
+
 # 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
 # It is allowed to specify more targets when calling make, including
@@ -954,7 +961,7 @@ ifneq ($(KBUILD_SRC),)
 endif
 
 # prepare2 creates a makefile if using a separate output directory
-prepare2: prepare3 outputmakefile
+prepare2: prepare3 outputmakefile asm-generic
 
 prepare1: prepare2 include/linux/version.h include/generated/utsrelease.h \
                    include/config/auto.conf
@@ -1028,7 +1035,7 @@ hdr-inst := -rR -f $(srctree)/scripts/Makefile.headersinst obj
 hdr-dst = $(if $(KBUILD_HEADERS), dst=include/asm-$(hdr-arch), dst=include/asm)
 
 PHONY += __headers
-__headers: include/linux/version.h scripts_basic FORCE
+__headers: include/linux/version.h scripts_basic asm-generic FORCE
 	$(Q)$(MAKE) $(build)=scripts build_unifdef
 
 PHONY += headers_install_all
@@ -1143,7 +1150,8 @@ CLEAN_FILES +=	vmlinux System.map \
                 .tmp_kallsyms* .tmp_version .tmp_vmlinux* .tmp_System.map
 
 # Directories & files removed with 'make mrproper'
-MRPROPER_DIRS  += include/config usr/include include/generated
+MRPROPER_DIRS  += include/config usr/include include/generated          \
+                  arch/*/include/generated
 MRPROPER_FILES += .config .config.old .version .old_version             \
                   include/linux/version.h                               \
 		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS

scripts/Makefile.asm-generic

@@ -0,0 +1,23 @@
+# include/asm-generic contains a lot of files that are used
+# verbatim by several architectures.
+#
+# This Makefile reads the file arch/$(SRCARCH)/include/asm/Kbuild
+# and for each file listed in this file with generic-y creates
+# a small wrapper file in $(obj) (arch/$(SRCARCH)/include/generated/asm)
+
+kbuild-file := $(srctree)/arch/$(SRCARCH)/include/asm/Kbuild
+include $(kbuild-file)
+
+include scripts/Kbuild.include
+
+# Create output directory if not already present
+_dummy := $(shell [ -d $(obj) ] || mkdir -p $(obj))
+
+quiet_cmd_wrap = WRAP    $@
+cmd_wrap = echo "\#include <asm-generic/$*.h>" >$@
+
+all: $(patsubst %, $(obj)/%, $(generic-y))
+
+$(obj)/%.h:
+	$(call cmd,wrap)
+

scripts/Makefile.headersinst

@@ -27,8 +27,13 @@ header-y      := $(filter-out %/, $(header-y))
 install-file  := $(install)/.install
 check-file    := $(install)/.check
 
+# generic-y list all files an architecture uses from asm-generic
+# Use this to build a list of headers which require a wrapper
+wrapper-files := $(filter $(header-y), $(generic-y))
+
 # all headers files for this dir
-all-files     := $(header-y) $(objhdr-y)
+header-y      := $(filter-out $(generic-y), $(header-y))
+all-files     := $(header-y) $(objhdr-y) $(wrapper-files)
 input-files   := $(addprefix $(srctree)/$(obj)/,$(header-y)) \
                  $(addprefix $(objtree)/$(obj)/,$(objhdr-y))
 output-files  := $(addprefix $(install)/, $(all-files))
@@ -47,6 +52,9 @@ quiet_cmd_install = INSTALL $(printdir) ($(words $(all-files))\
       cmd_install = \
         $(PERL) $< $(srctree)/$(obj) $(install) $(SRCARCH) $(header-y); \
         $(PERL) $< $(objtree)/$(obj) $(install) $(SRCARCH) $(objhdr-y); \
+        for F in $(wrapper-files); do                                   \
+                echo "\#include <asm-generic/$$F>" > $(install)/$$F;    \
+        done;                                                           \
         touch $@
 
 quiet_cmd_remove = REMOVE  $(unwanted)