Direct compile 16bit C code instead of including via .S files.

Create a ".code16gcc" directive in src/code16gcc.s and use
-Wa,src/code16gcc.s to tell gcc to compile directly to 16bit code.
This eliminates the need to compile the C code to assembler and
include in romlayout.S and vgaentry.S.  This also allows those two
assembler files to be compiled with debugging (-g) enabled.

Also, includes some Makefile cleanups.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/Makefile b/Makefile
index 513e8f1..07a1174 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 # SeaBIOS build system
 #
-# Copyright (C) 2008-2010  Kevin O'Connor <kevin@koconnor.net>
+# Copyright (C) 2008-2012  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU LGPLv3 license.
 
@@ -23,11 +23,11 @@
     biostables.c xen.c bmp.c
 SRC32SEG=util.c output.c pci.c pcibios.c apm.c stacks.c
 
+# Default compiler flags
 cc-option=$(shell if test -z "`$(1) $(2) -S -o /dev/null -xc /dev/null 2>&1`" \
     ; then echo "$(2)"; else echo "$(3)"; fi ;)
 
-# Default compiler flags
-COMMONCFLAGS = -I$(OUT) -Os -MD \
+COMMONCFLAGS = -I$(OUT) -Os -MD -g \
     -Wall -Wno-strict-aliasing -Wold-style-definition \
     $(call cc-option,$(CC),-Wtype-limits,) \
     -m32 -march=i386 -mregparm=3 -mpreferred-stack-boundary=2 \
@@ -38,14 +38,14 @@
 COMMONCFLAGS += $(call cc-option,$(CC),-fno-stack-protector,)
 COMMONCFLAGS += $(call cc-option,$(CC),-fno-stack-protector-all,)
 
-CFLAGS32FLAT = $(COMMONCFLAGS) -DMODE16=0 -DMODESEGMENT=0 -g -fomit-frame-pointer
+CFLAGS32FLAT = $(COMMONCFLAGS) -DMODE16=0 -DMODESEGMENT=0 -fomit-frame-pointer
 CFLAGSSEG = $(COMMONCFLAGS) -DMODESEGMENT=1 -fno-defer-pop \
     $(call cc-option,$(CC),-fno-jump-tables,-DMANUAL_NO_JUMP_TABLE) \
     $(call cc-option,$(CC),-fno-tree-switch-conversion,)
-CFLAGS32SEG = $(CFLAGSSEG) -DMODE16=0 -g -fomit-frame-pointer
-CFLAGS16INC = $(CFLAGSSEG) -DMODE16=1 \
+CFLAGS32SEG = $(CFLAGSSEG) -DMODE16=0 -fomit-frame-pointer
+CFLAGS16INC = $(CFLAGSSEG) -DMODE16=1 -Wa,src/code16gcc.s \
     $(call cc-option,$(CC),--param large-stack-frame=4,-fno-inline)
-CFLAGS16 = $(CFLAGS16INC) -g -fomit-frame-pointer
+CFLAGS16 = $(CFLAGS16INC) -fomit-frame-pointer
 
 # Run with "make V=1" to see the actual compile commands
 ifdef V
@@ -79,7 +79,8 @@
 vpath %.c src vgasrc
 vpath %.S src vgasrc
 
-################ Build rules
+
+################ Common build rules
 
 # Verify the gcc configuration and test if -fwhole-program works.
 TESTGCC:=$(shell CC="$(CC)" LD="$(LD)" tools/test-gcc.sh)
@@ -122,34 +123,37 @@
 
 $(OUT)%.s: %.c
 	@echo "  Compiling to assembler $@"
-	$(Q)$(CC) $(CFLAGS16INC) -S -c $< -o $@
+	$(Q)$(CC) $(CFLAGS16) -S -c $< -o $@
 
 $(OUT)%.lds: %.lds.S
 	@echo "  Precompiling $@"
 	$(Q)$(CPP) -P -D__ASSEMBLY__ $< -o $@
 
+
+################ Main BIOS build rules
+
 $(OUT)asm-offsets.s: $(OUT)autoconf.h
 
 $(OUT)asm-offsets.h: $(OUT)asm-offsets.s
 	@echo "  Generating offset file $@"
 	$(Q)./tools/gen-offsets.sh $< $@
 
-
-$(OUT)ccode.16.s: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS16) -S, $(addprefix src/, $(SRC16)),$@)
+$(OUT)ccode16.o: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS16), $(addprefix src/, $(SRC16)),$@)
 
 $(OUT)code32seg.o: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS32SEG), $(addprefix src/, $(SRC32SEG)),$@)
 
 $(OUT)ccode32flat.o: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS32FLAT), $(addprefix src/, $(SRC32FLAT)),$@)
 
-$(OUT)code16.o: romlayout.S $(OUT)ccode.16.s $(OUT)asm-offsets.h
+$(OUT)romlayout.o: romlayout.S $(OUT)asm-offsets.h
 	@echo "  Compiling (16bit) $@"
-	$(Q)$(CC) $(CFLAGS16INC) -c -D__ASSEMBLY__ $< -o $@
+	$(Q)$(CC) $(CFLAGS16) -c -D__ASSEMBLY__ $< -o $@
 
-$(OUT)romlayout16.lds: $(OUT)ccode32flat.o $(OUT)code32seg.o $(OUT)code16.o tools/layoutrom.py
+$(OUT)romlayout16.lds: $(OUT)ccode32flat.o $(OUT)code32seg.o $(OUT)ccode16.o $(OUT)romlayout.o tools/layoutrom.py
 	@echo "  Building ld scripts (version \"$(VERSION)\")"
 	$(Q)echo 'const char VERSION[] = "$(VERSION)";' > $(OUT)version.c
 	$(Q)$(CC) $(CFLAGS32FLAT) -c $(OUT)version.c -o $(OUT)version.o
 	$(Q)$(LD) -melf_i386 -r $(OUT)ccode32flat.o $(OUT)version.o -o $(OUT)code32flat.o
+	$(Q)$(LD) -melf_i386 -r $(OUT)ccode16.o $(OUT)romlayout.o -o $(OUT)code16.o
 	$(Q)$(OBJDUMP) -thr $(OUT)code32flat.o > $(OUT)code32flat.o.objdump
 	$(Q)$(OBJDUMP) -thr $(OUT)code32seg.o > $(OUT)code32seg.o.objdump
 	$(Q)$(OBJDUMP) -thr $(OUT)code16.o > $(OUT)code16.o.objdump
@@ -157,7 +161,7 @@
 
 # These are actually built by tools/layoutrom.py above, but by pulling them
 # into an extra rule we prevent make -j from spawning layoutrom.py 4 times.
-$(OUT)romlayout32seg.lds $(OUT)romlayout32flat.lds $(OUT)code32flat.o: $(OUT)romlayout16.lds
+$(OUT)romlayout32seg.lds $(OUT)romlayout32flat.lds $(OUT)code32flat.o $(OUT)code16.o: $(OUT)romlayout16.lds
 
 $(OUT)rom16.o: $(OUT)code16.o $(OUT)romlayout16.lds
 	@echo "  Linking $@"
@@ -187,17 +191,17 @@
     vgasrc/stdvga.c vgasrc/stdvgamodes.c vgasrc/stdvgaio.c \
     vgasrc/clext.c vgasrc/bochsvga.c vgasrc/geodevga.c
 
-CFLAGS16VGA = $(CFLAGS16INC) -g -Isrc
+CFLAGS16VGA = $(CFLAGS16INC) -Isrc
 
-$(OUT)vgaccode.16.s: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS16VGA) -S, $(SRCVGA),$@)
+$(OUT)vgaccode16.o: $(OUT)autoconf.h ; $(call whole-compile, $(CFLAGS16VGA), $(SRCVGA),$@)
 
-$(OUT)vgalayout16.o: vgaentry.S $(OUT)vgaccode.16.s $(OUT)asm-offsets.h
+$(OUT)vgaentry.o: vgaentry.S $(OUT)autoconf.h
 	@echo "  Compiling (16bit) $@"
-	$(Q)$(CC) $(CFLAGS16INC) -c -D__ASSEMBLY__ -Isrc $< -o $@
+	$(Q)$(CC) $(CFLAGS16VGA) -c -D__ASSEMBLY__ $< -o $@
 
-$(OUT)vgarom.o: $(OUT)vgalayout16.o $(OUT)vgalayout.lds
+$(OUT)vgarom.o: $(OUT)vgaccode16.o $(OUT)vgaentry.o $(OUT)vgalayout.lds
 	@echo "  Linking $@"
-	$(Q)$(LD) --gc-sections -T $(OUT)vgalayout.lds $(OUT)vgalayout16.o -o $@
+	$(Q)$(LD) --gc-sections -T $(OUT)vgalayout.lds $(OUT)vgaccode16.o $(OUT)vgaentry.o -o $@
 
 $(OUT)vgabios.bin.raw: $(OUT)vgarom.o
 	@echo "  Extracting binary $@"
@@ -207,7 +211,9 @@
 	@echo "  Finalizing rom $@"
 	$(Q)$(PYTHON) ./tools/buildrom.py $< $@
 
-####### dsdt build rules
+
+################ DSDT build rules
+
 src/%.hex: src/%.dsl ./tools/acpi_extract_preprocess.py ./tools/acpi_extract.py
 	@echo "Compiling DSDT"
 	$(Q)cpp -P $< > $(OUT)$*.dsl.i.orig
@@ -216,9 +222,9 @@
 	$(Q)$(PYTHON) ./tools/acpi_extract.py $(OUT)$*.lst > $(OUT)$*.off
 	$(Q)cat $(OUT)$*.off > $@
 
-$(OUT)ccode32flat.o: src/acpi-dsdt.hex src/ssdt-proc.hex src/ssdt-pcihp.hex
 
-####### Kconfig rules
+################ Kconfig rules
+
 define do-kconfig
 $(Q)mkdir -p $(OUT)/tools/kconfig/lxdialog
 $(Q)mkdir -p $(OUT)/include/config
@@ -230,7 +236,9 @@
 %onfig: ; $(call do-kconfig, $@)
 help: ; $(call do-kconfig, $@)
 
-####### Generic rules
+
+################ Generic rules
+
 clean:
 	$(Q)rm -rf $(OUT)