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SubjectRe: [RFC] Standard way of generating assembler offsets
Date
First patch to clean up Assembler offsets, as described in
http://marc.theaimsgroup.com/?l=linux-kernel&m=100219616028442&w=2

This patch is larger than normal because my testing highlighted a long
standing race in the top level kernel Makefile.

i386 patch. Yes, I know that doing asm-offsets.c for i386 is overkill,
it only needs a few values that "never" change so they can be hard
coded. However I need a reference implementation, plus the race needs
to be mitigated.

BTW, this is *much* cleaner in kbuild 2.5. Bits of the patch are
workarounds for recursive make problems and to handle mkdep not
processing Assembler dependencies :(.

Index: 11-pre4.1/Makefile
--- 11-pre4.1/Makefile Fri, 05 Oct 2001 15:05:09 +1000 kaos (linux-2.4/T/c/50_Makefile 1.1.2.15.1.2.2.25.2.2.1.17.1.4.1.29 644)
+++ 11-pre4.1(w)/Makefile Sat, 06 Oct 2001 15:07:25 +1000 kaos (linux-2.4/T/c/50_Makefile 1.1.2.15.1.2.2.25.2.2.1.17.1.4.1.29 644)
@@ -205,7 +205,8 @@ CLEAN_FILES = \
drivers/scsi/53c700-mem.c \
net/khttpd/make_times_h \
net/khttpd/times.h \
- submenu*
+ submenu* \
+ arch/$(ARCH)/asm-offsets.[sh]
# directories removed with 'make clean'
CLEAN_DIRS = \
modules
@@ -245,9 +246,9 @@ export CPPFLAGS CFLAGS AFLAGS
export NETWORKS DRIVERS LIBS HEAD LDFLAGS LINKFLAGS MAKEBOOT ASFLAGS

.S.s:
- $(CPP) $(AFLAGS) -traditional -o $*.s $<
+ $(CPP) $(AFLAGS) $(AFLAGS_$@) -traditional -o $@ $<
.S.o:
- $(CC) $(AFLAGS) -traditional -c -o $*.o $<
+ $(CC) $(AFLAGS) $(AFLAGS_$@) -traditional -c -o $@ $<

Version: dummy
@rm -f include/linux/compile.h
@@ -273,29 +274,63 @@ symlinks:
mkdir include/linux/modules; \
fi

-oldconfig: symlinks
+# There is a race here against anything built by the top level Makefile or by
+# arch/$(ARCH)/Makefile (directly included by the top level Makefile).
+
+# split-include changes timestamps on config settings without telling make.
+# Because make is not aware that config files have been changed, the timestamp
+# checks in .hdepend (see Rules.make) use the old times for config files.
+# Therefore anything built at the same time that split-include is running gets
+# wrong timestamps for config settings and for the include files that depend on
+# config settings.
+
+# I cannot completely fix this in kbuild 2.4 without moving most of the top
+# level Makefile into a second file and doing make -C on that file after
+# split-include has run. Explicitly running split-include after *config instead
+# of delaying until make dep mitigates the race, although it does not completely
+# remove it.
+
+# The race is not a problem for SUBDIRS processed from the top level Makefile
+# because split-include has completed before they are entered. However it is a
+# problem for top level builds and for directories invoked from
+# arch/$(ARCH)/Makefile without using SUBDIRS.
+
+# kbuild 2.5 has a clean separation between configuration (top level and
+# scripts/Makefile) and the rest of the kernel build, so it does not suffer from
+# this race. Also kbuild 2.5 splits arch/$(ARCH)/Makefile into definitions
+# (Makefile.defs.{no}config) and kernel building commands (Makefile.in).
+# KAO
+
+split_include := scripts/split-include include/linux/autoconf.h include/config && touch include/config/MARKER
+
+oldconfig: symlinks scripts/split-include
$(CONFIG_SHELL) scripts/Configure -d arch/$(ARCH)/config.in
+ @$(split_include)

-xconfig: symlinks
+xconfig: symlinks scripts/split-include
$(MAKE) -C scripts kconfig.tk
wish -f scripts/kconfig.tk
+ @$(split_include)

-menuconfig: include/linux/version.h symlinks
+menuconfig: include/linux/version.h symlinks scripts/split-include
$(MAKE) -C scripts/lxdialog all
$(CONFIG_SHELL) scripts/Menuconfig arch/$(ARCH)/config.in
+ @$(split_include)

-config: symlinks
+config: symlinks scripts/split-include
$(CONFIG_SHELL) scripts/Configure arch/$(ARCH)/config.in
+ @$(split_include)

include/config/MARKER: scripts/split-include include/linux/autoconf.h
- scripts/split-include include/linux/autoconf.h include/config
- @ touch include/config/MARKER
+ @$(split_include)

linuxsubdirs: $(patsubst %, _dir_%, $(SUBDIRS))

-$(patsubst %, _dir_%, $(SUBDIRS)) : dummy include/linux/version.h include/config/MARKER
+$(patsubst %, _dir_%, $(SUBDIRS)) : dummy include/linux/version.h include/config/MARKER before_subdirs
$(MAKE) CFLAGS="$(CFLAGS) $(CFLAGS_KERNEL)" -C $(patsubst _dir_%, %, $@)

+.PHONY: before_subdirs
+
$(TOPDIR)/include/linux/version.h: include/linux/version.h
$(TOPDIR)/include/linux/compile.h: include/linux/compile.h

@@ -356,7 +391,7 @@ endif
modules: $(patsubst %, _mod_%, $(SUBDIRS))

.PHONY: $(patsubst %, _mod_%, $(SUBDIRS))
-$(patsubst %, _mod_%, $(SUBDIRS)) : include/linux/version.h include/config/MARKER
+$(patsubst %, _mod_%, $(SUBDIRS)) : include/linux/version.h include/config/MARKER before_subdirs
$(MAKE) -C $(patsubst _mod_%, %, $@) CFLAGS="$(CFLAGS) $(MODFLAGS)" MAKING_MODULES=1 modules

.PHONY: modules_install
Index: 11-pre4.1/arch/i386/asm-offsets.c
--- 11-pre4.1/arch/i386/asm-offsets.c Sat, 06 Oct 2001 15:07:38 +1000 kaos ()
+++ 11-pre4.1(w)/arch/i386/asm-offsets.c Fri, 05 Oct 2001 21:53:18 +1000 kaos (linux-2.4/q/f/50_asm-offset 644)
@@ -0,0 +1,32 @@
+/*
+ * Generate definitions needed by assembly language modules.
+ * This code generates raw asm output which is post-processed to extract
+ * and format the required data.
+ */
+
+#include <linux/types.h>
+#include <linux/stddef.h>
+#include <linux/sched.h>
+
+/* Use marker if you need to separate the values later */
+
+#define DEFINE(sym, val, marker) \
+ asm volatile("\n-> " #sym " %0 " #val " " #marker : : "i" (val))
+
+#define BLANK() asm volatile("\n->" : : )
+
+int
+main(void)
+{
+ DEFINE(state, offsetof(struct task_struct, state),);
+ DEFINE(flags, offsetof(struct task_struct, flags),);
+ DEFINE(sigpending, offsetof(struct task_struct, sigpending),);
+ DEFINE(addr_limit, offsetof(struct task_struct, addr_limit),);
+ DEFINE(exec_domain, offsetof(struct task_struct, exec_domain),);
+ DEFINE(need_resched, offsetof(struct task_struct, need_resched),);
+ DEFINE(tsk_ptrace, offsetof(struct task_struct, ptrace),);
+ DEFINE(processor, offsetof(struct task_struct, processor),);
+ BLANK();
+ DEFINE(ENOSYS, ENOSYS,);
+ return 0;
+}
Index: 11-pre4.1/arch/i386/kernel/entry.S
--- 11-pre4.1/arch/i386/kernel/entry.S Mon, 01 Oct 2001 12:23:40 +1000 kaos (linux-2.4/S/c/24_entry.S 1.1.5.5 644)
+++ 11-pre4.1(w)/arch/i386/kernel/entry.S Sat, 06 Oct 2001 13:04:03 +1000 kaos (linux-2.4/S/c/24_entry.S 1.1.5.5 644)
@@ -68,20 +68,7 @@ IF_MASK = 0x00000200
NT_MASK = 0x00004000
VM_MASK = 0x00020000

-/*
- * these are offsets into the task-struct.
- */
-state = 0
-flags = 4
-sigpending = 8
-addr_limit = 12
-exec_domain = 16
-need_resched = 20
-tsk_ptrace = 24
-processor = 52
-
-ENOSYS = 38
-
+#include "asm-offsets.h"

#define SAVE_ALL \
cld; \
Index: 11-pre4.1/arch/i386/kernel/Makefile
--- 11-pre4.1/arch/i386/kernel/Makefile Wed, 19 Sep 2001 14:59:20 +1000 kaos (linux-2.4/S/c/21_Makefile 1.1.2.1 644)
+++ 11-pre4.1(w)/arch/i386/kernel/Makefile Fri, 05 Oct 2001 22:37:10 +1000 kaos (linux-2.4/S/c/21_Makefile 1.1.2.1 644)
@@ -8,7 +8,7 @@
# Note 2! The CFLAGS definitions are now in the main makefile...

.S.o:
- $(CC) $(AFLAGS) -traditional -c $< -o $*.o
+ $(CC) $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$@) -traditional -c $< -o $@

all: kernel.o head.o init_task.o

@@ -40,5 +40,8 @@ obj-$(CONFIG_SMP) += smp.o smpboot.o tr
obj-$(CONFIG_X86_LOCAL_APIC) += mpparse.o apic.o nmi.o
obj-$(CONFIG_X86_IO_APIC) += io_apic.o
obj-$(CONFIG_X86_VISWS_APIC) += visws_apic.o
+
+AFLAGS_entry.o += -I $(TOPDIR)/arch/$(ARCH)
+entry.o: $(TOPDIR)/arch/$(ARCH)/asm-offsets.h

include $(TOPDIR)/Rules.make
Index: 11-pre4.1/arch/i386/Makefile
--- 11-pre4.1/arch/i386/Makefile Wed, 18 Apr 2001 11:00:10 +1000 kaos (linux-2.4/T/c/37_Makefile 1.1.2.1.2.1 644)
+++ 11-pre4.1(w)/arch/i386/Makefile Sat, 06 Oct 2001 15:07:31 +1000 kaos (linux-2.4/T/c/37_Makefile 1.1.2.1.2.1 644)
@@ -145,3 +145,45 @@ archmrproper:

archdep:
@$(MAKEBOOT) dep
+
+# Convert raw asm offsets into something that can be included as
+# assembler definitions. It converts
+# -> symbol $value source
+# into
+# symbol = value /* 0xvalue source */
+
+arch/$(ARCH)/asm-offsets.h: arch/$(ARCH)/asm-offsets.s
+ @echo Creating $@
+ @set -e; \
+ (echo "#ifndef __ASM_OFFSETS_H__"; \
+ echo "#define __ASM_OFFSETS_H__"; \
+ echo "/*"; \
+ echo " * DO NOT MODIFY"; \
+ echo " *"; \
+ echo " * This file was generated by arch/$(ARCH)/Makefile."; \
+ echo " *"; \
+ echo " */"; \
+ echo ""; \
+ awk "/^->\$$/{printf(\"\\n\");} \
+ /^-> /{ \
+ sym = \$$2; \
+ val = \$$3; \
+ sub(/^\\\$$/, \"\", val); \
+ \$$1 = \"\"; \
+ \$$2 = \"\"; \
+ \$$3 = \"\"; \
+ printf(\"%-20s = %3d\\t\\t\\t/* 0x%x\\t%s */\\n\", \
+ sym, val, val, \$$0) \
+ }"; \
+ echo ""; \
+ echo "#endif"; \
+ ) < $< > $@;
+
+arch/$(ARCH)/asm-offsets.s: include/config/MARKER \
+ include/linux/sched.h \
+ include/linux/types.h \
+ include/linux/stddef.h
+
+# Kludge to prevent subdirs from being processed before asm-offsets.h is created.
+# I hate recursive make! KAO.
+before_subdirs: arch/$(ARCH)/asm-offsets.h
-
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