kbuild: add a script to remove stale generated files

We maintain .gitignore and Makefiles so build artifacts are properly
ignored by Git, and cleaned up by 'make clean'. However, the code is
always changing; generated files are often moved to another directory,
or removed when they become unnecessary. Such garbage files tend to be
left over in the source tree because people usually git-pull without
cleaning the tree.

This is not only the noise for 'git status', but also a build issue
in some cases.

One solution is to remove a stale file like commit 223c24a7dba9 ("kbuild:
Automatically remove stale <linux/version.h> file") did. Such workaround
should be removed after a while, but we forget about that if we scatter
the workaround code in random places.

So, this commit adds a new script to collect cleanings of stale files.

As a start point, move the code in arch/arm/boot/compressed/Makefile
into this script.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

3 files changed, 36 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 6eafedd7efc6..9f5a3cac63e7 100644
--- a/Makefile
+++ b/Makefile
@@ -1225,7 +1225,7 @@ PHONY += prepare archprepare
 
 archprepare: outputmakefile archheaders archscripts scripts include/config/kernel.release \
 	asm-generic $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
-	include/generated/autoconf.h
+	include/generated/autoconf.h remove-stale-files
 
 prepare0: archprepare
 	$(Q)$(MAKE) $(build)=scripts/mod
@@ -1234,6 +1234,10 @@ prepare0: archprepare
 # All the preparing..
 prepare: prepare0 prepare-objtool prepare-resolve_btfids
 
+PHONY += remove-stale-files
+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
 
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index fd94e27ba4fa..182b300e3f8a 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -96,13 +96,6 @@ endif
 $(foreach o, $(libfdt_objs) atags_to_fdt.o fdt_check_mem_start.o, \
 	$(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
 
-# These were previously generated C files. When you are building the kernel
-# with O=, make sure to remove the stale files in the output tree. Otherwise,
-# the build system wrongly compiles the stale ones.
-ifdef building_out_of_srctree
-$(shell rm -f $(addprefix $(obj)/, fdt_rw.c fdt_ro.c fdt_wip.c fdt.c))
-endif
-
 targets       := vmlinux vmlinux.lds piggy_data piggy.o \
 		 lib1funcs.o ashldi3.o bswapsdi2.o \
 		 head.o $(OBJS)
diff --git a/scripts/remove-stale-files b/scripts/remove-stale-files
new file mode 100755
index 000000000000..c3eb81c3f7de
--- /dev/null
+++ b/scripts/remove-stale-files
@@ -0,0 +1,31 @@
+#!/bin/sh
+
+set -e
+
+# When you move, remove or rename generated files, you probably also update
+# .gitignore and cleaning rules in the Makefile. This is the right thing
+# to do. However, people usually do 'git pull', 'git bisect', etc. without
+# running 'make clean'. Then, the stale generated files are left over, often
+# causing build issues.
+#
+# Also, 'git status' shows such stale build artifacts as untracked files.
+# What is worse, some people send a wrong patch to get them back to .gitignore
+# without checking the commit history.
+#
+# So, when you (re)move generated files, please move the cleaning rules from
+# the Makefile to this script. This is run before Kbuild starts building
+# anything, so people will not be annoyed by such garbage files.
+#
+# This script is not intended to grow endlessly. Rather, it is a temporary scrap
+# yard. Stale files stay in this file for a while (for some release cycles?),
+# then will be really dead and removed from the code base entirely.
+
+# These were previously generated source files. When you are building the kernel
+# with O=, make sure to remove the stale files in the output tree. Otherwise,
+# the build system wrongly compiles the stale ones.
+if [ -n "${building_out_of_srctree}" ]; then
+	for f in fdt_rw.c fdt_ro.c fdt_wip.c fdt.c
+	do
+		rm -f arch/arm/boot/compressed/${f}
+	done
+fi