Hello,
I decided to try out the header precompilation feature of newer GCCs
to see if it would speed up kernel building. Following is a patch
which 1) adds headers target to top-level makefile, 2) allows and
compiles .h files into .h.gch using gcc. When gcc compiles the normal
C files, it looks for the precompiled headers by default, and no
change is needed.
I am not a kbuild expert, so I want to ask if my changes are done
correctly. It seems to me that the build in fact slows down
tremendously, and I don't know why. It seems that the last make does
nothing at all for a long time before finally starting as normal, so
most of the extra time comes from before anything is compiled at
all. For instance, just compiling the kernel/ subdir with and without
the precompiled headers:
make clean scripts/; time make kernel/
real0m27.174s
user0m23.760s
sys 0m3.003s
make clean scripts/; make headers; time make kernel/
real0m53.076s
user0m25.211s
sys 0m4.155s
By the way, according to the GCC manual [1], Only one precompiled
header can be used in a particular compilation, which, if I interpret
it correctly, might make header precompilation useless for the kernel
anyway. But here's my attempt (I hope the patch comes through okay).
Kind regards,
Vegard Nossum
[1] http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html
From 41d6eeab27442cec728596123bb6f4ecb143b9a3 Mon Sep 17 00:00:00 2001
From: Vegard Nossum [EMAIL PROTECTED]
Date: Wed, 30 May 2007 19:01:10 +0200
Subject: [PATCH] [kbuild] Added support for precompiled headers
---
Makefile | 13 -
scripts/Makefile.build | 18 ++
2 files changed, 30 insertions(+), 1 deletions(-)
diff --git a/Makefile b/Makefile
index 562a909..48f2b68 100644
--- a/Makefile
+++ b/Makefile
@@ -1046,7 +1046,7 @@ clean: archclean $(clean-dirs)
@find . $(RCS_FIND_IGNORE) \
\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
- -o -name '*.symtypes' \) \
+ -o -name '*.symtypes' -o -name '*.h.gch' \) \
-type f -print | xargs rm -f
# mrproper - Delete all generated files, including .config
@@ -1116,6 +1116,7 @@ help:
@echo ' cscope - Generate cscope index'
@echo ' kernelrelease - Output the release version string'
@echo ' kernelversion - Output the version stored in Makefile'
+ @echo ' headers - Build precompiled headers'
@if [ -r $(srctree)/include/asm-$(ARCH)/Kbuild ]; then \
echo ' headers_install - Install sanitised kernel headers to
INSTALL_HDR_PATH'; \
echo '(default: $(INSTALL_HDR_PATH))'; \
@@ -1252,6 +1253,14 @@ prepare: ;
scripts: ;
endif # KBUILD_EXTMOD
+
+# Compile headers
+# ---
+
+headers: FORCE
+ $(Q)$(MAKE) -i $(build)=include
+
+
# Generate tags for editors
# ---
@@ -1424,6 +1433,8 @@ else
target-dir = $(if $(KBUILD_EXTMOD),$(dir $),$(dir $@))
endif
+%.h.gch: %.h prepare scripts FORCE
+ $(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.s: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.i: %.c prepare scripts FORCE
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a525112..b9ec464 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -78,10 +78,16 @@ ifneq ($(strip $(obj-y) $(obj-m) $(obj-n) $(obj-)
$(lib-target)),)
builtin-target := $(obj)/built-in.o
endif
+# Extract subdirs and header targets from header-y
+subdir-ym += $(patsubst %,$(src)/%,$(patsubst %/,%,$(filter %/,$(header-y
+cheader-y += $(patsubst %.h,$(patsubst %/,%,$(obj))/%.h.gch,$(filter
%.h,$(header-y)))
+cheader-y += $(patsubst %.h,$(patsubst %/,%,$(obj))/%.h.gch,$(filter
%.h,$(unifdef-y)))
+
# We keep a list of all modules in $(MODVERDIR)
__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
$(if $(KBUILD_MODULES),$(obj-m)) \
+$(cheader-y) \
$(subdir-ym) $(always)
@:
@@ -97,6 +103,18 @@ ifneq ($(KBUILD_CHECKSRC),0)
endif
+# Compile header files (.h)
+# ---
+
+quiet_cmd_cc_h_gch_h = CC $(quiet_modtag) $@
+ cmd_cc_h_gch_h = $(CC) $(c_flags) -o $@ $
+
+$(obj)/%.h.gch: $(src)/%.h FORCE
+ $(call if_changed_dep,cc_h_gch_h)
+
+targets += $(cheader-y)
+
+
# Compile C sources (.c)
# ---
--
1.5.0.6
-
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