kbuild: Don't reset timestamps in include/generated if not needed

Use filechk to generate asm-offsets.h and bounds.h. Based on a patch by
Valdis Kletnieks.

Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Acked-By: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

diff --git a/Kbuild b/Kbuild
index ab8ded92e870f55290d4d8283e4cbb1b849f8a58..96d062906c052fbb89d5b79ad8556a7a77772924 100644 (file)
--- a/Kbuild
+++ b/Kbuild
@@ -13,8 +13,9 @@ define sed-y
        s:->::; p;}"
 endef
 
-quiet_cmd_offsets = GEN     $@
-define cmd_offsets
+# Use filechk to avoid rebuilds when a header changes, but the resulting file
+# does not
+define filechk_offsets
        (set -e; \
         echo "#ifndef $2"; \
         echo "#define $2"; \
@@ -24,9 +25,9 @@ define cmd_offsets
         echo " * This file was generated by Kbuild"; \
         echo " */"; \
         echo ""; \
-        sed -ne $(sed-y) $<; \
+        sed -ne $(sed-y); \
         echo ""; \
-        echo "#endif" ) > $@
+        echo "#endif" )
 endef
 
 #####
@@ -42,9 +43,8 @@ kernel/bounds.s: kernel/bounds.c FORCE
        $(Q)mkdir -p $(dir $@)
        $(call if_changed_dep,cc_s_c)
 
-$(obj)/$(bounds-file): kernel/bounds.s Kbuild
-       $(Q)mkdir -p $(dir $@)
-       $(call cmd,offsets,__LINUX_BOUNDS_H__)
+$(obj)/$(bounds-file): kernel/bounds.s FORCE
+       $(call filechk,offsets,__LINUX_BOUNDS_H__)
 
 #####
 # 2) Generate asm-offsets.h
@@ -62,8 +62,8 @@ arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
        $(Q)mkdir -p $(dir $@)
        $(call if_changed_dep,cc_s_c)
 
-$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s Kbuild
-       $(call cmd,offsets,__ASM_OFFSETS_H__)
+$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
+       $(call filechk,offsets,__ASM_OFFSETS_H__)
 
 #####
 # 3) Check for missing system calls