From: Christoph Lameter <clameter@sgi.com>
Subject: Kbuild: Create a way to create preprocessor constants from C expressions

The use of enums create constants that are not available to the preprocessor
when building the kernel (f.e. MAX_NR_ZONES).

Arch code already has a way to export constants calculated to the
preprocessor through the asm-offsets.c file. Generate something
similar for the core kernel through kbuild.

V2->V3:
- Sam graciously fixed up the Kbuild portion
- Break the chicken-egg dilemma by not including bounds.h if we are
  generating it.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 Kbuild          |   56 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 kernel/bounds.c |   19 +++++++++++++++++++
 2 files changed, 67 insertions(+), 8 deletions(-)

Index: linux-2.6.25-rc5-mm1/kernel/bounds.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.25-rc5-mm1/kernel/bounds.c	2008-03-18 09:48:53.690621912 -0700
@@ -0,0 +1,19 @@
+/*
+ * Generate definitions needed by the preprocessor.
+ * This code generates raw asm output which is post-processed
+ * to extract and format the required data.
+ */
+
+#define __GENERATING_BOUNDS_H
+/* Include headers that define the enum constants of interest */
+
+#define DEFINE(sym, val) \
+        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
+
+#define BLANK() asm volatile("\n->" : : )
+
+void foo(void)
+{
+	/* The enum constants to put into include/linux/bounds.h */
+	/* End of constants */
+}
Index: linux-2.6.25-rc5-mm1/Kbuild
===================================================================
--- linux-2.6.25-rc5-mm1.orig/Kbuild	2008-03-18 00:28:53.795162043 -0700
+++ linux-2.6.25-rc5-mm1/Kbuild	2008-03-18 00:28:55.627170881 -0700
@@ -1,19 +1,54 @@
 #
 # Kbuild for top-level directory of the kernel
 # This file takes care of the following:
-# 1) Generate asm-offsets.h
-# 2) Check for missing system calls
+# 1) Generate bounds.h
+# 2) Generate asm-offsets.h (may need bounds.h)
+# 3) Check for missing system calls
 
 #####
-# 1) Generate asm-offsets.h
+# 1) Generate bounds.h
+
+bounds-file := include/linux/bounds.h
+
+always  := $(bounds-file)
+targets := $(bounds-file) kernel/bounds.s
+
+quiet_cmd_bounds = GEN     $@
+define cmd_bounds
+	(set -e; \
+	 echo "#ifndef __LINUX_BOUNDS_H__"; \
+	 echo "#define __LINUX_BOUNDS_H__"; \
+	 echo "/*"; \
+	 echo " * DO NOT MODIFY."; \
+	 echo " *"; \
+	 echo " * This file was generated by Kbuild"; \
+	 echo " *"; \
+	 echo " */"; \
+	 echo ""; \
+	 sed -ne $(sed-y) $<; \
+	 echo ""; \
+	 echo "#endif" ) > $@
+endef
+
+# We use internal kbuild rules to avoid the "is up to date" message from make
+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,bounds)
+
+#####
+# 2) Generate asm-offsets.h
 #
 
 offsets-file := include/asm-$(SRCARCH)/asm-offsets.h
 
-always  := $(offsets-file)
-targets := $(offsets-file)
+always  += $(offsets-file)
+targets += $(offsets-file)
 targets += arch/$(SRCARCH)/kernel/asm-offsets.s
-clean-files := $(addprefix $(objtree)/,$(targets))
+
 
 # Default sed regexp - multiline due to syntax constraints
 define sed-y
@@ -40,7 +75,8 @@ define cmd_offsets
 endef
 
 # We use internal kbuild rules to avoid the "is up to date" message from make
-arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c FORCE
+arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
+                                      $(obj)/$(bounds-file) FORCE
 	$(Q)mkdir -p $(dir $@)
 	$(call if_changed_dep,cc_s_c)
 
@@ -49,7 +85,7 @@ $(obj)/$(offsets-file): arch/$(SRCARCH)/
 	$(call cmd,offsets)
 
 #####
-# 2) Check for missing system calls
+# 3) Check for missing system calls
 #
 
 quiet_cmd_syscalls = CALL    $<
@@ -58,3 +94,7 @@ quiet_cmd_syscalls = CALL    $<
 PHONY += missing-syscalls
 missing-syscalls: scripts/checksyscalls.sh FORCE
 	$(call cmd,syscalls)
+
+# Delete all targets during make clean
+clean-files := $(addprefix $(objtree)/,$(targets))
+