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ARM: 9404/1: arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

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The current arm32 architecture does not yet support the
HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. arm32 is widely used in
embedded scenarios, and enabling this feature would be beneficial for
reducing the size of the kernel image.

In order to make this work, we keep the necessary tables by annotating
them with KEEP, also it requires further changes to linker script to KEEP
some tables and wildcard compiler generated sections into the right place.
When using ld.lld for linking, KEEP is not recognized within the OVERLAY
command, and Ard proposed a concise method to solve this problem.

It boots normally with defconfig, vexpress_defconfig and tinyconfig.

The size comparison of zImage is as follows:
defconfig       vexpress_defconfig      tinyconfig
5137712         5138024                 424192          no dce
5032560         4997824                 298384          dce
2.0%            2.7%                    29.7%           shrink

When using smaller config file, there is a significant reduction in the
size of the zImage.

We also tested this patch on a commercially available single-board
computer, and the comparison is as follows:
a15eb_config
2161384         no dce
2092240         dce
3.2%            shrink

The zImage size has been reduced by approximately 3.2%, which is 70KB on
2.1M.

Signed-off-by: Yuntao Liu <liuyuntao12@huawei.com>
Tested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Yuntao Liu 2024-06-03 16:37:50 +01:00 committed by Russell King (Oracle)
parent 9ac7ba12d3
commit ed0f941022
7 changed files with 15 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/arm/Kconfig
View File

@ -115,6 +115,7 @@ config ARM
select HAVE_KERNEL_XZ
select HAVE_KPROBES if !XIP_KERNEL && !CPU_ENDIAN_BE32 && !CPU_V7M
select HAVE_KRETPROBES if HAVE_KPROBES
select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI
select HAVE_OPTPROBES if !THUMB2_KERNEL

2
arch/arm/boot/compressed/vmlinux.lds.S
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@ -125,7 +125,7 @@ SECTIONS
. = BSS_START;
__bss_start = .;
.bss : { *(.bss) }
.bss : { *(.bss .bss.*) }
_end = .;
. = ALIGN(8); /* the stack must be 64-bit aligned */

2
arch/arm/include/asm/vmlinux.lds.h
View File

@ -42,7 +42,7 @@
#define PROC_INFO \
. = ALIGN(4); \
__proc_info_begin = .; \
*(.proc.info.init) \
KEEP(*(.proc.info.init)) \
__proc_info_end = .;
#define IDMAP_TEXT \

3
arch/arm/kernel/entry-armv.S
View File

@ -1065,6 +1065,7 @@ vector_addrexcptn:
.globl vector_fiq
.section .vectors, "ax", %progbits
.reloc .text, R_ARM_NONE, .
W(b) vector_rst
W(b) vector_und
ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_swi )
@ -1078,6 +1079,7 @@ THUMB( .reloc ., R_ARM_THM_PC12, .L__vector_swi )
#ifdef CONFIG_HARDEN_BRANCH_HISTORY
.section .vectors.bhb.loop8, "ax", %progbits
.reloc .text, R_ARM_NONE, .
W(b) vector_rst
W(b) vector_bhb_loop8_und
ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_bhb_loop8_swi )
@ -1090,6 +1092,7 @@ THUMB( .reloc ., R_ARM_THM_PC12, .L__vector_bhb_loop8_swi )
W(b) vector_bhb_loop8_fiq
.section .vectors.bhb.bpiall, "ax", %progbits
.reloc .text, R_ARM_NONE, .
W(b) vector_rst
W(b) vector_bhb_bpiall_und
ARM( .reloc ., R_ARM_LDR_PC_G0, .L__vector_bhb_bpiall_swi )

4
arch/arm/kernel/vmlinux-xip.lds.S
View File

@ -63,7 +63,7 @@ SECTIONS
. = ALIGN(4);
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
__start___ex_table = .;
ARM_MMU_KEEP(*(__ex_table))
ARM_MMU_KEEP(KEEP(*(__ex_table)))
__stop___ex_table = .;
}
@ -83,7 +83,7 @@ SECTIONS
}
.init.arch.info : {
__arch_info_begin = .;
*(.arch.info.init)
KEEP(*(.arch.info.init))
__arch_info_end = .;
}
.init.tagtable : {

6
arch/arm/kernel/vmlinux.lds.S
View File

@ -74,7 +74,7 @@ SECTIONS
. = ALIGN(4);
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
__start___ex_table = .;
ARM_MMU_KEEP(*(__ex_table))
ARM_MMU_KEEP(KEEP(*(__ex_table)))
__stop___ex_table = .;
}
@ -99,7 +99,7 @@ SECTIONS
}
.init.arch.info : {
__arch_info_begin = .;
*(.arch.info.init)
KEEP(*(.arch.info.init))
__arch_info_end = .;
}
.init.tagtable : {
@ -116,7 +116,7 @@ SECTIONS
#endif
.init.pv_table : {
__pv_table_begin = .;
*(.pv_table)
KEEP(*(.pv_table))
__pv_table_end = .;
}

4
drivers/firmware/efi/libstub/Makefile
View File

@ -56,6 +56,10 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
# disable LTO
KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
# The .data section would be renamed to .data.efistub, therefore, remove
# `-fdata-sections` flag from KBUILD_CFLAGS_KERNEL
KBUILD_CFLAGS_KERNEL := $(filter-out -fdata-sections, $(KBUILD_CFLAGS_KERNEL))
lib-y := efi-stub-helper.o gop.o secureboot.o tpm.o \
file.o mem.o random.o randomalloc.o pci.o \
skip_spaces.o lib-cmdline.o lib-ctype.o \