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arm: Have the linker garbage-collect unused functions and variables

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This patch activates -ffunction-sections and -fdata-sections for the
compiler and --gc-sections for the linker. This will strip out all
unused functions and static/global variables from the final binaries and
reduce the amount of data we need to read over SPI.

A quick test with ToT images shows a 2.5k (13%) / 10k (29%) / 12k (28%)
reduction on Nyan and 3k (38%) / 23k (50%) / 13k (29%) on Pit,
respectively for bootblock / romstage / ramstage.

BUG=None
TEST=Made sure Nyan and Pit still boot to kernel.

Change-Id: I052411d4ad190d0395921ac4d4677341fb91568a
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/177111
This commit is contained in:
Julius Werner 2013-10-15 17:36:17 -07:00 • committed by chrome-internal-fetch
commit 5635b13877
4 changed files with 36 additions and 32 deletions
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14
src/arch/arm/Makefile.inc
View file

@ -82,7 +82,7 @@ ramstage-srcs += src/mainboard/$(MAINBOARDDIR)/mainboard.c
################################################################################
# Common recipes for all stages
CFLAGS += -mno-unaligned-access
CFLAGS += -mno-unaligned-access -ffunction-sections -fdata-sections
$(objcbfs)/%.bin: $(objcbfs)/%.elf
@printf " OBJCOPY $(subst $(obj)/,,$(@))\n"
@ -160,9 +160,9 @@ endif
$(objcbfs)/bootblock.debug: $(src)/arch/arm/bootblock.ld $(obj)/ldoptions $$(bootblock-objs) $(obj)/config.h
@printf " LINK $(subst $(obj)/,,$(@))\n"
ifeq ($(CONFIG_COMPILER_LLVM_CLANG),y)
$(LD) -m armelf_linux_eabi -static -o $@ -L$(obj) $< -T $(src)/arch/arm/bootblock.ld
$(LD) -m armelf_linux_eabi --gc-sections -static -o $@ -L$(obj) $< -T $(src)/arch/arm/bootblock.ld
else
$(CC) $(CFLAGS) -nostartfiles -static -o $@ -L$(obj) -T $(src)/arch/arm/bootblock.ld -Wl,--start-group $(bootblock-objs) -Wl,--end-group
$(CC) $(CFLAGS) -nostartfiles -Wl,--gc-sections -static -o $@ -L$(obj) -T $(src)/arch/arm/bootblock.ld -Wl,--start-group $(bootblock-objs) -Wl,--end-group
endif
################################################################################
@ -171,9 +171,9 @@ endif
$(objcbfs)/romstage.debug: $$(romstage-objs) $(src)/arch/arm/romstage.ld $(obj)/ldoptions
@printf " LINK $(subst $(obj)/,,$(@))\n"
ifeq ($(CONFIG_COMPILER_LLVM_CLANG),y)
$(LD) -nostdlib -nostartfiles -static -o $@ -L$(obj) $(romstage-objs) -T $(src)/arch/arm/romstage.ld
$(LD) -nostdlib -nostartfiles --gc-sections -static -o $@ -L$(obj) $(romstage-objs) -T $(src)/arch/arm/romstage.ld
else
$(CC) $(CFLAGS) -nostartfiles -static -o $@ -L$(obj) -T $(src)/arch/arm/romstage.ld -Wl,--start-group $(romstage-objs) -Wl,--end-group
$(CC) $(CFLAGS) -nostartfiles -Wl,--gc-sections -static -o $@ -L$(obj) -T $(src)/arch/arm/romstage.ld -Wl,--start-group $(romstage-objs) -Wl,--end-group
endif
################################################################################
@ -182,9 +182,9 @@ endif
$(objcbfs)/coreboot_ram.debug: $$(ramstage-objs) $(src)/arch/arm/coreboot_ram.ld $(obj)/ldoptions
@printf " CC $(subst $(obj)/,,$(@))\n"
ifeq ($(CONFIG_COMPILER_LLVM_CLANG),y)
$(LD) -m -m armelf_linux_eabi -o $@ --wrap __divdi3 --wrap __udivdi3 --wrap __moddi3 --wrap __umoddi3 --wrap __uidiv --start-group $(ramstage-objs) --end-group -T $(src)/arch/arm/coreboot_ram.ld
$(LD) -m -m armelf_linux_eabi --gc-sections -o $@ --wrap __divdi3 --wrap __udivdi3 --wrap __moddi3 --wrap __umoddi3 --wrap __uidiv --start-group $(ramstage-objs) --end-group -T $(src)/arch/arm/coreboot_ram.ld
else
$(CC) $(CFLAGS) -nostartfiles -static -o $@ -L$(obj) -Wl,--start-group $(ramstage-objs) -Wl,--end-group -T $(src)/arch/arm/coreboot_ram.ld
$(CC) $(CFLAGS) -nostartfiles -Wl,--gc-sections -static -o $@ -L$(obj) -Wl,--start-group $(ramstage-objs) -Wl,--end-group -T $(src)/arch/arm/coreboot_ram.ld
endif
################################################################################

20
src/arch/arm/bootblock.ld
View file

@ -23,23 +23,25 @@ OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
INCLUDE ldoptions
ENTRY(_start)
TARGET(binary)
SECTIONS
{
ROMLOC = CONFIG_BOOTBLOCK_BASE;
. = CONFIG_BOOTBLOCK_BASE;
/* This section might be better named .setup */
.rom ROMLOC : {
_rom = .;
.bootblock . : {
*(.start);
*(.id);
KEEP(*(.id));
*(.text);
*(.text.*);
*(.rom.text);
*(.rom.data);
*(.rom.data.*);
*(.rodata);
*(.rodata.*);
_erom = .;
*(.data);
*(.data.*);
*(.bss);
*(.bss.*);
*(.sbss);
*(.sbss.*);
} = 0xff
/DISCARD/ : {

22
src/arch/arm/coreboot_ram.ld
View file

@ -43,7 +43,7 @@ SECTIONS
.ctors : {
. = ALIGN(0x100);
__CTOR_LIST__ = .;
*(.ctors);
KEEP(*(.ctors));
LONG(0);
__CTOR_END__ = .;
}
@ -52,17 +52,17 @@ SECTIONS
_rodata = .;
. = ALIGN(4);
console_drivers = .;
*(.rodata.console_drivers)
KEEP(*(.rodata.console_drivers));
econsole_drivers = . ;
. = ALIGN(4);
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)
*(.rodata.*)
@ -82,6 +82,7 @@ SECTIONS
.data : {
_data = .;
*(.data)
*(.data.*)
_edata = .;
}
@ -89,26 +90,27 @@ SECTIONS
* initialized on startup. (typically uninitialized global variables)
* crt0.S fills between _bss and _ebss with zeroes.
*/
_bss = .;
.bss . : {
_bss = .;
*(.bss)
*(.bss.*)
*(.sbss)
*(COMMON)
*(.sbss.*)
_ebss = .;
}
_ebss = .;
_end = .;
/* coreboot really "ends" here. Only heap and stack are placed after
* this line.
*/
_heap = .;
.heap . : {
_heap = .;
/* Reserve CONFIG_HEAP_SIZE bytes for the heap */
. = CONFIG_HEAP_SIZE ;
. = ALIGN(4);
_eheap = .;
}
_eheap = .;
/* The ram segment. This includes all memory used by the memory
* resident copy of coreboot, except the tables that are produced on

12
src/arch/arm/romstage.ld
View file

@ -36,19 +36,19 @@ SECTIONS
. = CONFIG_ROMSTAGE_BASE;
.romtext . : {
_rom = .;
_start = .;
*(.text.stage_entry.arm);
*(.text.startup);
*(.text);
*(.text.*);
}
.romdata . : {
*(.rodata);
*(.machine_param);
*(.rodata.*);
*(.data);
*(.data.*);
. = ALIGN(8);
_erom = .;
}
/* bss does not contain data, it is just a space that should be zero
@ -59,12 +59,12 @@ SECTIONS
. = ALIGN(8);
_bss = .;
*(.bss)
*(.bss.*)
*(.sbss)
*(COMMON)
*(.sbss.*)
_ebss = .;
}
_ebss = .;
_end = .;
/* Discard the sections we don't need/want */