kbuild: add syscall table generation to scripts/Makefile.asm-headers

There are 11 copies of arch/*/kernel/syscalls/Makefile that all implement
the same basic logic in a somewhat awkward way.

I tried out various ways of unifying the existing copies and ended up
with something that hooks into the logic for generating the redirections
to asm-generic headers. This gives a nicer syntax of being able to list
the generated files in $(syscall-y) inside of arch/*/include/asm/Kbuild
instead of both $(generated-y) in that place and also in another
Makefile.

The configuration for which syscall.tbl file to use and which ABIs to
enable is now done in arch/*/kernel/Makefile.syscalls. I have done
patches for all architectures and made sure that the new generic
rules implement a superset of all the architecture specific corner
cases.

ince the header file is not specific to asm-generic/*.h redirects
now, I ended up renaming the file to scripts/Makefile.asm-headers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Makefile

@@ -1219,7 +1219,7 @@ remove-stale-files:
 	$(Q)$(srctree)/scripts/remove-stale-files
 
 # Support for using generic headers in asm-generic
-asm-generic := -f $(srctree)/scripts/Makefile.asm-generic obj
+asm-generic := -f $(srctree)/scripts/Makefile.asm-headers obj
 
 PHONY += asm-generic uapi-asm-generic
 asm-generic: uapi-asm-generic

scripts/Makefile.asm-headers

@@ -0,0 +1,98 @@
+# SPDX-License-Identifier: GPL-2.0
+# include/asm-generic contains a lot of files that are used
+# verbatim by several architectures.
+#
+# This Makefile generates arch/$(SRCARCH)/include/generated/(uapi/)/asm
+# headers from multiple sources:
+#  - a small wrapper to include the corresponding asm-generic/*.h
+#    is generated for each file listed as generic-y
+#  - uapi/asm/unistd_*.h files listed as syscalls-y are generated from
+#    syscall.tbl with the __NR_* macros
+#  - Corresponding asm/syscall_table_*.h are generated from the same input
+
+PHONY := all
+all:
+
+src := $(srctree)/$(subst /generated,,$(obj))
+
+syscall_abis_32  += common,32
+syscall_abis_64  += common,64
+syscalltbl := $(srctree)/scripts/syscall.tbl
+syshdr-args := --emit-nr
+
+# let architectures override $(syscall_abis_%) and $(syscalltbl)
+-include $(srctree)/arch/$(SRCARCH)/kernel/Makefile.syscalls
+include $(srctree)/scripts/Kbuild.include
+-include $(kbuild-file)
+
+syshdr := $(srctree)/scripts/syscallhdr.sh
+systbl := $(srctree)/scripts/syscalltbl.sh
+
+# $(generic)/Kbuild lists mandatory-y. Exclude um since it is a special case.
+ifneq ($(SRCARCH),um)
+include $(srctree)/$(generic)/Kbuild
+endif
+
+redundant := $(filter $(mandatory-y) $(generated-y), $(generic-y))
+redundant += $(foreach f, $(generic-y), $(if $(wildcard $(src)/$(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 $(src)/$(f)),,$(f)))
+
+generic-y   := $(addprefix $(obj)/, $(generic-y))
+syscall-y   := $(addprefix $(obj)/, $(syscall-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) $(syscall-y),$(old-headers))
+
+quiet_cmd_wrap = WRAP    $@
+      cmd_wrap = echo "\#include <asm-generic/$*.h>" > $@
+
+quiet_cmd_remove = REMOVE  $(unwanted)
+      cmd_remove = rm -f $(unwanted)
+
+quiet_cmd_syshdr = SYSHDR  $@
+      cmd_syshdr = $(CONFIG_SHELL) $(syshdr) \
+		   $(if $(syshdr-args-$*),$(syshdr-args-$*),$(syshdr-args)) \
+		   $(if $(syscall_compat),--prefix "compat$*_") \
+		   --abis $(subst $(space),$(comma),$(strip $(syscall_abis_$*))) \
+		   $< $@
+
+quiet_cmd_systbl = SYSTBL  $@
+      cmd_systbl = $(CONFIG_SHELL) $(systbl) \
+		   $(if $(systbl-args-$*),$(systbl-args-$*),$(systbl-args)) \
+		   --abis $(subst $(space),$(comma),$(strip $(syscall_abis_$*))) \
+		   $< $@
+
+all: $(generic-y) $(syscall-y)
+	$(if $(unwanted),$(call cmd,remove))
+	@:
+
+$(obj)/%.h: $(srctree)/$(generic)/%.h
+	$(call cmd,wrap)
+
+$(obj)/unistd_%.h: $(syscalltbl) $(syshdr) FORCE
+	$(call if_changed,syshdr)
+
+$(obj)/unistd_compat_%.h: syscall_compat:=1
+$(obj)/unistd_compat_%.h: $(syscalltbl) $(syshdr) FORCE
+	$(call if_changed,syshdr)
+
+$(obj)/syscall_table_%.h: $(syscalltbl) $(systbl) FORCE
+	$(call if_changed,systbl)
+
+# Create output directory. Skip it if at least one old header exists
+# since we know the output directory already exists.
+ifeq ($(old-headers),)
+$(shell mkdir -p $(obj))
+endif
+
+FORCE:
+
+.PHONY: $(PHONY)