coreboot: x86: enable gc-sections

Garbage collected sections allow for trimming the size of the
binaries as well as allowing for not needing to config off
unused functions. To that end, on a rambi build the following
differences are observed:

$ diff -up \
	<(readelf -l coreboot-builds/google_rambi/cbfs/fallback/ramstage.elf) \
	<(readelf -l coreboot-builds/google_rambi_gc_sections/cbfs/fallback/ramstage.elf)
--- /dev/fd/63  2015-03-10 12:07:27.927985430 -0500
+++ /dev/fd/62  2015-03-10 12:07:27.927985430 -0500
@@ -6,9 +6,9 @@ There are 4 program headers, starting at
 Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg
Align
   LOAD           0x001000 0x00000000 0x00000000 0x00040 0x00040 RWE 0
-  LOAD           0x001040 0x00000040 0x00000040 0x34560 0x34560 RWE 0
-  LOAD           0x0355a0 0x000345a0 0x000345a0 0x02578 0x02578 RWE 0
-  LOAD           0x037b18 0x00036b18 0x00036b18 0x00000 0x0b560     0
+  LOAD           0x001040 0x00000040 0x00000040 0x2cbf8 0x2cbf8 RWE 0
+  LOAD           0x02dc38 0x0002cc38 0x0002cc38 0x02208 0x02208 RWE 0
+  LOAD           0x02fe40 0x0002ee40 0x0002ee40 0x00000 0x0a888     0

  Section to Segment mapping:
   Segment Sections...

$ diff -up \
	<(readelf -l coreboot-builds/google_rambi/cbfs/fallback/romstage.elf) \
	<(readelf -l coreboot-builds/google_rambi_gc_sections/cbfs/fallback/romstage.elf)
--- /dev/fd/63  2015-03-10 12:08:16.855985880 -0500
+++ /dev/fd/62  2015-03-10 12:08:16.851985880 -0500
@@ -5,8 +5,8 @@ There are 1 program headers, starting at

 Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg
Align
-  LOAD           0x000060 0xfff20000 0xfff20000 0x08b81 0x08b81 R E
   0x10
+  LOAD           0x000060 0xfff20000 0xfff20000 0x06300 0x06300 R E
0x10

  Section to Segment mapping:
   Segment Sections...
-   00     .rom .text
+   00     .rom

The following warnings needed to be applied to CFLAGS_common because for
some reason gcc was miraculously emitting the warnings with the
unrelated *-sections options:
  -Wno-unused-but-set-variable

Change-Id: I210784fdfc273ce4cb9927352cbd5a51be3c6929
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/8635
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

Makefile.inc

@@ -253,7 +253,7 @@ CPPFLAGS_common += -include $(src)/include/kconfig.h
 CFLAGS_common += -pipe -g -nostdinc
 CFLAGS_common += -nostdlib -Wall -Wundef -Wstrict-prototypes -Wmissing-prototypes
 CFLAGS_common += -Wwrite-strings -Wredundant-decls -Wno-trigraphs
-CFLAGS_common += -Wstrict-aliasing -Wshadow
+CFLAGS_common += -Wstrict-aliasing -Wshadow -Wno-unused-but-set-variable
 ifeq ($(CONFIG_WARNINGS_ARE_ERRORS),y)
 CFLAGS_common += -Werror
 endif

src/arch/x86/Makefile.inc

@@ -27,11 +27,7 @@ subdirs-y += boot
 subdirs-y += lib
 subdirs-y += smp
 
-ifeq ($(CONFIG_COMPILER_GCC),y)
-DISASSEMBLY=-Wa,-acdlns
-else
 DISASSEMBLY=-Wa,--divide
-endif
 
 OPTION_TABLE_H:=
 ifeq ($(CONFIG_HAVE_OPTION_TABLE),y)
@@ -214,7 +210,7 @@ $(objcbfs)/romstage_null.debug: $$(romstage-objs) $(objgenerated)/romstage_null.
 
 $(objcbfs)/romstage.debug: $$(romstage-objs) $(objgenerated)/romstage.ld $$(romstage-libs)
 	@printf "    LINK       $(subst $(obj)/,,$(@))\n"
-	$(LD_romstage) -nostdlib -nostartfiles -static -o $@ -L$(obj) $(COMPILER_RT_FLAGS_romstage) --start-group $(romstage-objs) $(romstage-libs) $(COMPILER_RT_romstage) --end-group -T $(objgenerated)/romstage.ld
+	$(LD_romstage) --gc-sections -nostdlib -nostartfiles -static -o $@ -L$(obj) $(COMPILER_RT_FLAGS_romstage) --start-group $(romstage-objs) $(romstage-libs) $(COMPILER_RT_romstage) --end-group -T $(objgenerated)/romstage.ld
 
 $(objgenerated)/romstage_null.ld: $$(ldscripts) $(obj)/ldoptions
 	@printf "    GEN        $(subst $(obj)/,,$(@))\n"
@@ -310,7 +306,7 @@ else
 
 $(objcbfs)/ramstage.debug: $(objgenerated)/ramstage.o $(src)/arch/x86/ramstage.ld
 	@printf "    CC         $(subst $(obj)/,,$(@))\n"
-	$(LD_ramstage) -o $@ -L$(obj) $< -T $(src)/arch/x86/ramstage.ld
+	$(LD_ramstage) --gc-sections -o $@ -L$(obj) $< -T $(src)/arch/x86/ramstage.ld
 
 endif
 

src/arch/x86/init/romstage.ld

@@ -30,13 +30,16 @@ SECTIONS
 	.rom . : {
 		_rom = .;
 		*(.rom.text);
+		*(.rom.text.*);
+		*(.text);
+		*(.text.*);
 		*(.rom.data);
 		*(.rodata);
 		*(.rodata.*);
 		*(.rom.data.*);
 		. = ALIGN(16);
 		_car_migrate_start = .;
-		*(.car.migrate);
+		KEEP(*(.car.migrate));
 		LONG(0);
 		_car_migrate_end = .;
 		. = ALIGN(16);
@@ -73,7 +76,7 @@ SECTIONS
 	. = 0xffffff00;
 	.illegal_globals . : {
 		*(EXCLUDE_FILE (*/libagesa.*.a: */buildOpts.romstage.o */agesawrapper.romstage.o */vendorcode/amd/agesa/* */vendorcode/amd/cimx/*) .data)
-		*(.data.*)
+		*(EXCLUDE_FILE (*/libagesa.*.a: */buildOpts.romstage.o */agesawrapper.romstage.o */vendorcode/amd/agesa/* */vendorcode/amd/cimx/*) .data.*)
 		*(.bss)
 		*(.bss.*)
 		*(.sbss)

src/arch/x86/ramstage.ld

@@ -42,7 +42,7 @@ SECTIONS
 	.ctors : {
 		. = ALIGN(0x100);
 		__CTOR_LIST__ = .;
-		*(.ctors);
+		KEEP(*(.ctors));
 		LONG(0);
 		__CTOR_END__ = .;
 	}
@@ -55,13 +55,13 @@ SECTIONS
 		 * section names the equivalent changes need to made to
 		 * rmodule.ld. */
 		pci_drivers = . ;
-		*(.rodata.pci_driver)
+		KEEP(*(.rodata.pci_driver));
 		epci_drivers = . ;
 		cpu_drivers = . ;
-		*(.rodata.cpu_driver)
+		KEEP(*(.rodata.cpu_driver));
 		ecpu_drivers = . ;
 		_bs_init_begin = .;
-		*(.bs_init)
+		KEEP(*(.bs_init));
 		_bs_init_end = .;
 
 		*(.rodata)
@@ -82,6 +82,7 @@ SECTIONS
 	.data : {
 		_data = .;
 		*(.data)
+		*(.data.*)
 		_edata = .;
 	}
 
@@ -92,7 +93,9 @@ SECTIONS
 	_bss = .;
 	.bss . : {
 		*(.bss)
+		*(.bss.*)
 		*(.sbss)
+		*(.sbss.*)
 		*(COMMON)
 	}
 	_ebss = .;

src/lib/Makefile.inc

@@ -119,7 +119,7 @@ ramstage-y += rmodule.c
 romstage-$(CONFIG_RELOCATABLE_RAMSTAGE) += rmodule.c
 
 RMODULE_LDSCRIPT := $(src)/lib/rmodule.ld
-RMODULE_LDFLAGS  := -nostartfiles --emit-relocs -z defs -Bsymbolic -T$(RMODULE_LDSCRIPT)
+RMODULE_LDFLAGS  := -nostartfiles --gc-sections --emit-relocs -z defs -Bsymbolic -T$(RMODULE_LDSCRIPT)
 
 # rmodule_link_rules is a function that should be called with:
 # (1) the object name to link

src/lib/rmodule.ld

@@ -14,6 +14,8 @@
 
 BASE_ADDRESS = 0x00000;
 
+ENTRY(__rmodule_entry);
+
 SECTIONS
 {
 	. = BASE_ADDRESS;
@@ -38,15 +40,15 @@ SECTIONS
 		 * ramstage.ld should be made here as well. */
 		. = ALIGN(8);
 		pci_drivers = . ;
-		*(.rodata.pci_driver)
+		KEEP(*(.rodata.pci_driver));
 		epci_drivers = . ;
 		. = ALIGN(8);
 		cpu_drivers = . ;
-		*(.rodata.cpu_driver)
+		KEEP(*(.rodata.cpu_driver));
 		ecpu_drivers = . ;
 		. = ALIGN(8);
 		_bs_init_begin = .;
-		*(.bs_init)
+		KEEP(*(.bs_init));
 		_bs_init_end = .;
 
 		. = ALIGN(8);
@@ -59,7 +61,7 @@ SECTIONS
 		 * to a module, however there has to be an prior agreement
 		 * on how to interpret the parameters. */
 		_module_params_begin = .;
-		*(.module_parameters);
+		KEEP(*(.module_parameters));
 		_module_params_end = .;
 		. = ALIGN(8);
 

toolchain.inc

@@ -66,6 +66,8 @@ CFLAGS_arm64 := -ffunction-sections -fdata-sections
 
 CFLAGS_mipsel   := -mips32r2 -G 0
 
+CFLAGS_x86_32 := -ffunction-sections -fdata-sections
+
 toolchain_to_dir = \
 	$(foreach arch,$(ARCH_SUPPORTED),\
 	$(eval CPPFLAGS_$(arch) += \