[PATCH v5 1/2] xen: asm-generic support

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Some headers are shared between individual architectures or are empty.
To avoid duplication of these headers, asm-generic is introduced.

With the following patch, an architecture uses generic headers
mentioned in the file arch/$(ARCH)/include/asm/Makefile

To use a generic header is needed to add to
arch/$(ARCH)/include/asm/Makefile :
        generic-y += <name-of-header-file.h>

For each mentioned header in arch/$(ARCH)/include/asm/Makefile,
the necessary wrapper in arch/$(ARCH)/include/generated/asm will be
generated.

As the base Makefile.asm-generic from Linux kernel was taken.
( 06c2afb862f9da8 "Linux 6.5-rc1" ).

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V5:
 - Update the commit message
 - Update SPDX license in Makefile.
 - Remove code related to UML
 - Include $(src)/Makefile instead of $(kbuild-file) 
 - Update comment message in Makefile.asm-generic
 - Update .gitignore
 - Update path to generated headers in CFLAGS.
 - Use the latest version of Linux's Makefile.asm-generic
---
Changes in V4:
 - introduce asm-generic support
 - update commit message
---
Changes in V3:
 - Rename stubs dir to asm-generic
---
Changes in V2:
 - Nothing changed.
---
 .gitignore                       |  1 +
 xen/Makefile                     | 10 +++++-
 xen/scripts/Makefile.asm-generic | 53 ++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 xen/scripts/Makefile.asm-generic

diff --git a/.gitignore b/.gitignore
index 50273adb8d..287166f8fc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -267,6 +267,7 @@ xen/arch/*/efi/efi.h
 xen/arch/*/efi/pe.c
 xen/arch/*/efi/runtime.c
 xen/arch/*/include/asm/asm-offsets.h
+xen/arch/*/include/generated
 xen/build-dir-cppcheck/
 xen/common/config_data.S
 xen/common/config.gz
diff --git a/xen/Makefile b/xen/Makefile
index f57e5a596c..a86b64303d 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -438,6 +438,7 @@ ifdef building_out_of_srctree
 endif
 CFLAGS += -I$(srctree)/include
 CFLAGS += -I$(srctree)/arch/$(SRCARCH)/include
+CFLAGS += -I$(objtree)/arch/$(SRCARCH)/include/generated
 
 # Note that link order matters!
 ALL_OBJS-y                := common/built_in.o
@@ -580,6 +581,7 @@ _clean:
        rm -f $(TARGET).efi $(TARGET).efi.map $(TARGET).efi.elf 
$(TARGET).efi.stripped
        rm -f asm-offsets.s arch/*/include/asm/asm-offsets.h
        rm -f .banner .allconfig.tmp include/xen/compile.h
+       rm -rf $(objtree)/arch/*/include/generated
 
 .PHONY: _distclean
 _distclean: clean
@@ -589,7 +591,7 @@ $(TARGET).gz: $(TARGET)
        gzip -n -f -9 < $< > $@.new
        mv $@.new $@
 
-$(TARGET): outputmakefile FORCE
+$(TARGET): outputmakefile asm-generic FORCE
        $(Q)$(MAKE) $(build)=tools
        $(Q)$(MAKE) $(build)=. include/xen/compile.h
        $(Q)$(MAKE) $(build)=include all
@@ -667,6 +669,12 @@ endif # need-sub-make
 PHONY += FORCE
 FORCE:
 
+# 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
+
 # Declare the contents of the PHONY variable as phony.  We keep that
 # information in a variable so we can use it in if_changed and friends.
 .PHONY: $(PHONY)
diff --git a/xen/scripts/Makefile.asm-generic b/xen/scripts/Makefile.asm-generic
new file mode 100644
index 0000000000..92a3a741c5
--- /dev/null
+++ b/xen/scripts/Makefile.asm-generic
@@ -0,0 +1,53 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# include/asm-generic contains a lot of files that are used
+# verbatim by several architectures.
+#
+# This Makefile reads the file arch/$(SRCARCH)/include/asm/Makefile
+# and for each file listed in this file with generic-y creates
+# a small wrapper file in arch/$(SRCARCH)/include/generated/asm.
+
+PHONY := all
+all:
+
+src := $(subst /generated,,$(obj))
+
+include $(srctree)/scripts/Kbuild.include
+-include $(src)/Makefile
+
+redundant := $(filter $(mandatory-y) $(generated-y), $(generic-y))
+redundant += $(foreach f, $(generic-y), $(if $(wildcard 
$(srctree)/$(src)/$(f)),$(f)))
+redundant := $(sort $(redundant))
+$(if $(redundant),\
+       $(warning redundant generic-y found in $(src)/Kbuild: $(redundant)))
+
+# If arch does not implement mandatory headers, fallback to asm-generic ones.
+mandatory-y := $(filter-out $(generated-y), $(mandatory-y))
+generic-y   += $(foreach f, $(mandatory-y), $(if $(wildcard 
$(srctree)/$(src)/$(f)),,$(f)))
+
+generic-y   := $(addprefix $(obj)/, $(generic-y))
+generated-y := $(addprefix $(obj)/, $(generated-y))
+
+# Remove stale wrappers when the corresponding files are removed from generic-y
+old-headers := $(wildcard $(obj)/*.h)
+unwanted    := $(filter-out $(generic-y) $(generated-y),$(old-headers))
+
+quiet_cmd_wrap = WRAP    $@
+      cmd_wrap = echo "\#include <asm-generic/$*.h>" > $@
+
+quiet_cmd_remove = REMOVE  $(unwanted)
+      cmd_remove = rm -f $(unwanted)
+
+all: $(generic-y)
+       $(if $(unwanted),$(call cmd,remove))
+       @:
+
+$(obj)/%.h:
+       $(call cmd,wrap)
+
+# Create output directory. Skip it if at least one old header exists
+# since we know the output directory already exists.
+ifeq ($(old-headers),)
+$(shell mkdir -p $(obj))
+endif
+
+.PHONY: $(PHONY)
-- 
2.41.0