kheaders: Do not regenerate archive if config is not changed

Linus reported an issue that doing an allmodconfig was causing the
kheaders archive to be regenerated even though the config is the same.
This patch fixes the issue by ignoring the config-related header files
for "knowing when to regenerate based on timestamps".  Instead, if the
CONFIG_X_Y option really changes, then we there are the
include/config/X/Y.h which will already tells us "if a config really
changed". So we don't really need these files for regeneration detection
anyway, and ignoring them fixes Linus's issue.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/gen_kheaders.sh

@@ -31,9 +31,8 @@ arch/$SRCARCH/include/
 
 # This block is useful for debugging the incremental builds.
 # Uncomment it for debugging.
-# iter=1
-# if [ ! -f /tmp/iter ]; then echo 1 > /tmp/iter;
-# else; 	iter=$(($(cat /tmp/iter) + 1)); fi
+# if [ ! -f /tmp/iter ]; then iter=1; echo 1 > /tmp/iter;
+# else iter=$(($(cat /tmp/iter) + 1)); echo $iter > /tmp/iter; fi
 # find $src_file_list -type f | xargs ls -lR > /tmp/src-ls-$iter
 # find $obj_file_list -type f | xargs ls -lR > /tmp/obj-ls-$iter
 
@@ -43,10 +42,18 @@ arch/$SRCARCH/include/
 pushd $kroot > /dev/null
 src_files_md5="$(find $src_file_list -type f                       |
 		grep -v "include/generated/compile.h"		   |
+		grep -v "include/generated/autoconf.h"		   |
+		grep -v "include/config/auto.conf"		   |
+		grep -v "include/config/auto.conf.cmd"		   |
+		grep -v "include/config/tristate.conf"		   |
 		xargs ls -lR | md5sum | cut -d ' ' -f1)"
 popd > /dev/null
 obj_files_md5="$(find $obj_file_list -type f                       |
 		grep -v "include/generated/compile.h"		   |
+		grep -v "include/generated/autoconf.h"		   |
+		grep -v "include/config/auto.conf"                 |
+		grep -v "include/config/auto.conf.cmd"		   |
+		grep -v "include/config/tristate.conf"		   |
 		xargs ls -lR | md5sum | cut -d ' ' -f1)"
 
 if [ -f $tarfile ]; then tarfile_md5="$(md5sum $tarfile | cut -d ' ' -f1)"; fi
@@ -82,7 +89,7 @@ find $cpio_dir -type f -print0 |
 
 tar -Jcf $tarfile -C $cpio_dir/ . > /dev/null
 
-echo "$src_files_md5" > kernel/kheaders.md5
+echo "$src_files_md5" >  kernel/kheaders.md5
 echo "$obj_files_md5" >> kernel/kheaders.md5
 echo "$(md5sum $tarfile | cut -d ' ' -f1)" >> kernel/kheaders.md5