Commit ed0f9410 authored by Yuntao Liu's avatar Yuntao Liu Committed by Russell King (Oracle)
Browse files

ARM: 9404/1: arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION 



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: default avatarYuntao Liu <liuyuntao12@huawei.com>
Tested-by: default avatarArnd Bergmann <arnd@arndb.de>
Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
parent 9ac7ba12

arch/arm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/arm/boot/compressed/vmlinux.lds.S

+1 −1
Original line number Diff line number Diff line
@@ -125,7 +125,7 @@ SECTIONS 


  . = BSS_START;

  __bss_start = .;

  .bss			: { *(.bss) }

  .bss			: { *(.bss .bss.*) }

  _end = .;



  . = ALIGN(8);		/* the stack must be 64-bit aligned */

arch/arm/include/asm/vmlinux.lds.h

+1 −1
Original line number Diff line number Diff line
@@ -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							\

arch/arm/kernel/entry-armv.S

+3 −0
Original line number Diff line number Diff line
@@ -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	)

arch/arm/kernel/vmlinux-xip.lds.S

+2 −2
Original line number Diff line number Diff line
@@ -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 : {