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linux/arch/arm/kernel/vmlinux-xip.lds.S
Yuntao Liu ed0f941022 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: 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>
2024-06-10 12:01:33 +01:00

197 lines
4.7 KiB
ArmAsm

/* SPDX-License-Identifier: GPL-2.0 */
/* ld script to make ARM Linux kernel
* taken from the i386 version by Russell King
* Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
*/
/* No __ro_after_init data in the .rodata section - which will always be ro */
#define RO_AFTER_INIT_DATA
#include <linux/sizes.h>
#include <asm/vmlinux.lds.h>
#include <asm/cache.h>
#include <asm/thread_info.h>
#include <asm/page.h>
#include <asm/mpu.h>
OUTPUT_ARCH(arm)
ENTRY(stext)
#ifndef __ARMEB__
jiffies = jiffies_64;
#else
jiffies = jiffies_64 + 4;
#endif
SECTIONS
{
/*
* XXX: The linker does not define how output sections are
* assigned to input sections when there are multiple statements
* matching the same input section name. There is no documented
* order of matching.
*
* unwind exit sections must be discarded before the rest of the
* unwind sections get included.
*/
/DISCARD/ : {
ARM_DISCARD
*(.alt.smp.init)
*(.pv_table)
#ifndef CONFIG_ARM_UNWIND
*(.ARM.exidx) *(.ARM.exidx.*)
*(.ARM.extab) *(.ARM.extab.*)
#endif
}
. = XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR);
_xiprom = .; /* XIP ROM area to be mapped */
.head.text : {
_text = .;
HEAD_TEXT
}
.text : { /* Real text segment */
_stext = .; /* Text and read-only data */
ARM_TEXT
}
RO_DATA(PAGE_SIZE)
. = ALIGN(4);
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
__start___ex_table = .;
ARM_MMU_KEEP(KEEP(*(__ex_table)))
__stop___ex_table = .;
}
#ifdef CONFIG_ARM_UNWIND
ARM_UNWIND_SECTIONS
#endif
_etext = .; /* End of text and rodata section */
ARM_VECTORS
INIT_TEXT_SECTION(8)
.exit.text : {
ARM_EXIT_KEEP(EXIT_TEXT)
}
.init.proc.info : {
ARM_CPU_DISCARD(PROC_INFO)
}
.init.arch.info : {
__arch_info_begin = .;
KEEP(*(.arch.info.init))
__arch_info_end = .;
}
.init.tagtable : {
__tagtable_begin = .;
*(.taglist.init)
__tagtable_end = .;
}
.init.rodata : {
INIT_SETUP(16)
INIT_CALLS
CON_INITCALL
INIT_RAM_FS
}
#ifdef CONFIG_ARM_MPU
. = ALIGN(SZ_128K);
#endif
_exiprom = .; /* End of XIP ROM area */
/*
* From this point, stuff is considered writable and will be copied to RAM
*/
__data_loc = ALIGN(4); /* location in file */
. = PAGE_OFFSET + TEXT_OFFSET; /* location in memory */
#undef LOAD_OFFSET
#define LOAD_OFFSET (PAGE_OFFSET + TEXT_OFFSET - __data_loc)
. = ALIGN(THREAD_SIZE);
_sdata = .;
RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
.data.ro_after_init : AT(ADDR(.data.ro_after_init) - LOAD_OFFSET) {
*(.data..ro_after_init)
}
_edata = .;
. = ALIGN(PAGE_SIZE);
__init_begin = .;
.init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {
INIT_DATA
}
.exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) {
ARM_EXIT_KEEP(EXIT_DATA)
}
#ifdef CONFIG_SMP
PERCPU_SECTION(L1_CACHE_BYTES)
#endif
#ifdef CONFIG_HAVE_TCM
ARM_TCM
#endif
/*
* End of copied data. We need a dummy section to get its LMA.
* Also located before final ALIGN() as trailing padding is not stored
* in the resulting binary file and useless to copy.
*/
.data.endmark : AT(ADDR(.data.endmark) - LOAD_OFFSET) { }
_edata_loc = LOADADDR(.data.endmark);
. = ALIGN(PAGE_SIZE);
__init_end = .;
BSS_SECTION(0, 0, 8)
#ifdef CONFIG_ARM_MPU
. = ALIGN(PMSAv8_MINALIGN);
#endif
_end = .;
STABS_DEBUG
DWARF_DEBUG
ARM_DETAILS
ARM_ASSERTS
}
/*
* These must never be empty
* If you have to comment these two assert statements out, your
* binutils is too old (for other reasons as well)
*/
ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support")
#ifndef CONFIG_COMPILE_TEST
ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")
#endif
#ifdef CONFIG_XIP_DEFLATED_DATA
/*
* The .bss is used as a stack area for __inflate_kernel_data() whose stack
* frame is 9568 bytes. Make sure it has extra room left.
*/
ASSERT((_end - __bss_start) >= 12288, ".bss too small for CONFIG_XIP_DEFLATED_DATA")
#endif
#if defined(CONFIG_ARM_MPU) && !defined(CONFIG_COMPILE_TEST)
/*
* Due to PMSAv7 restriction on base address and size we have to
* enforce minimal alignment restrictions. It was seen that weaker
* alignment restriction on _xiprom will likely force XIP address
* space spawns multiple MPU regions thus it is likely we run in
* situation when we are reprogramming MPU region we run on with
* something which doesn't cover reprogramming code itself, so as soon
* as we update MPU settings we'd immediately try to execute straight
* from background region which is XN.
* It seem that alignment in 1M should suit most users.
* _exiprom is aligned as 1/8 of 1M so can be covered by subregion
* disable
*/
ASSERT(!(_xiprom & (SZ_1M - 1)), "XIP start address may cause MPU programming issues")
ASSERT(!(_exiprom & (SZ_128K - 1)), "XIP end address may cause MPU programming issues")
#endif