[PATCH 1/3] time: move timeconst.h into include/generated

[Nicholas Mc Guire <hofrat@osadl.org>]

kernel/time/timeconst.h is moved to include/generated/ and generated in
an early build stage by top level Kbuild. This allows using timeconst.h
in an earlier stage of the build.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Thanks to Joe Perches <joe@perches.com> for suggesting this approach and
catching the unconditional rebuild (should be fixed here now properly) as well
 as for his review comments on the first attempts.

Some questions:
 * Kbuild - is passing in arguments to .bc files via pipe and read(); 
   rather than using multiple files acceptable or is there some reason
   for the original multifile solution that Im overlooking ?
 * conditional rebuild of timeconst.h with $(call filechk,gentimeconst)
   not really clear if this is going to do all rebuilds that could be 
   necessary and not clear how to verify this. currently only checked by
   1) defconfig -> build -> rebuild -> CHK is executed timeconst.h unmodified
   2) defconfig -> build -> change HZ -> rebuild -> UPD timeconst.h resulting
      in a rebuild of most files.

Patch was compile tested for x86_64_defconfig,multi_v7_defconfig, 
ppc64_defconfig, and boot/run
tested on x86_64. Further a test-case with an invalid HZ value to trigger the 
error output in kernel/time/timeconst.bc was run.

Patch is against 4.0-rc6 (localversion-next is -next-20150402)

 Kbuild                   |   30 +++++++++++++++++++++++++-----
 kernel/time/Makefile     |   17 +----------------
 kernel/time/time.c       |    2 +-
 kernel/time/timeconst.bc |    3 ++-
 4 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/Kbuild b/Kbuild
index 96d0629..4e1ed0b 100644
--- a/Kbuild
+++ b/Kbuild
@@ -2,8 +2,9 @@
 # Kbuild for top-level directory of the kernel
 # This file takes care of the following:
 # 1) Generate bounds.h
-# 2) Generate asm-offsets.h (may need bounds.h)
-# 3) Check for missing system calls
+# 2) Generate timeconst.h
+# 3) Generate asm-offsets.h (may need bounds.h)
+# 4) Check for missing system calls
 
 # Default sed regexp - multiline due to syntax constraints
 define sed-y
@@ -47,7 +48,26 @@ $(obj)/$(bounds-file): kernel/bounds.s FORCE
 	$(call filechk,offsets,__LINUX_BOUNDS_H__)
 
 #####
-# 2) Generate asm-offsets.h
+# 2) Generate timeconst.h
+
+timeconst-file := include/generated/timeconst.h
+
+always  += $(timeconst-file)
+targets += $(timeconst-file)
+
+quiet_cmd_gentimeconst = GEN     $@
+define cmd_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< ) > $@
+endef
+define filechk_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< ) 
+endef
+
+$(obj)/$(timeconst-file): kernel/time/timeconst.bc FORCE
+	$(call filechk,gentimeconst)
+
+#####
+# 3) Generate asm-offsets.h
 #
 
 offsets-file := include/generated/asm-offsets.h
@@ -66,7 +86,7 @@ $(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
 	$(call filechk,offsets,__ASM_OFFSETS_H__)
 
 #####
-# 3) Check for missing system calls
+# 4) Check for missing system calls
 #
 
 always += missing-syscalls
@@ -79,4 +99,4 @@ missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
 	$(call cmd,syscalls)
 
 # Keep these two files during make clean
-no-clean-files := $(bounds-file) $(offsets-file)
+no-clean-files := $(bounds-file) $(offsets-file) $(timeconst-file)
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 01f0312..ffc4cc3 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -13,19 +13,4 @@ obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
 
-$(obj)/time.o: $(obj)/timeconst.h
-
-quiet_cmd_hzfile = HZFILE  $@
-      cmd_hzfile = echo "hz=$(CONFIG_HZ)" > $@
-
-targets += hz.bc
-$(obj)/hz.bc: $(objtree)/include/config/hz.h FORCE
-	$(call if_changed,hzfile)
-
-quiet_cmd_bc  = BC      $@
-      cmd_bc  = bc -q $(filter-out FORCE,$^) > $@
-
-targets += timeconst.h
-$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
-	$(call if_changed,bc)
-
+$(obj)/time.o: $(objtree)/include/config/
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 2c85b77..4fa1d26 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -41,7 +41,7 @@
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
-#include "timeconst.h"
+#include <generated/timeconst.h>
 #include "timekeeping.h"
 
 /*
diff --git a/kernel/time/timeconst.bc b/kernel/time/timeconst.bc
index 511bdf2..c7388de 100644
--- a/kernel/time/timeconst.bc
+++ b/kernel/time/timeconst.bc
@@ -50,7 +50,7 @@ define timeconst(hz) {
 	print "#include <linux/types.h>\n\n"
 
 	print "#if HZ != ", hz, "\n"
-	print "#error \qkernel/timeconst.h has the wrong HZ value!\q\n"
+	print "#error \qinclude/generated/timeconst.h has the wrong HZ value!\q\n"
 	print "#endif\n\n"
 
 	if (hz < 2) {
@@ -105,4 +105,5 @@ define timeconst(hz) {
 	halt
 }
 
+hz = read();
 timeconst(hz)
-- 
1.7.10.4