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arm64: linker: move data section between rodata and bss

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Having .data after .bss creates a big empty gap in zephyr.bin to provide
proper offset for the data section. Reversing them allows for dropping
.bss from zephyr.bin's output as it is typically done, saving precious
flash memory space.

For demonstration purpose, let's consider those changes:

|--- a/samples/hello_world/src/main.c
|+++ b/samples/hello_world/src/main.c
|@@ -6,9 +6,12 @@
|
| #include <stdio.h>
|
|+int dummybuf[1024 * 1024];
|+
| int main(void)
| {
| 	printf("Hello World! %s\n", CONFIG_BOARD_TARGET);
|+	dummybuf[0] = 42;
|
| 	return 0;
| }

Before this commit:

$ ls -l build/zephyr/zephyr.bin
-rwxr-xr-x 1 nico nico 4561908 Aug  2 15:13 build/zephyr/zephyr.bin*

After this commit:

$ ls -l build/zephyr/zephyr.bin
-rwxr-xr-x 1 nico nico 37028 Aug  2 15:17 build/zephyr/zephyr.bin*

While at it, remove some more repetitive comments with no value.
Also defaults CONFIG_LINKER_LAST_SECTION_ID to n as it otherwise screws
everything up for the same reason as above.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2024-07-30 01:28:27 -04:00 • committed by Fabio Baltieri
commit 87f68b4dfe
2 changed files with 33 additions and 54 deletions
Download patch file Download diff file Expand all files Collapse all files

2
Kconfig.zephyr
View file

@ -275,7 +275,7 @@ config LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT
config LINKER_LAST_SECTION_ID
bool "Last section identifier"
default y
default y if !ARM64
depends on ARM || ARM64 || RISCV
help
If enabled, the last section will contain an identifier.

85
include/zephyr/arch/arm64/scripts/linker.ld
View file

@ -161,12 +161,10 @@ SECTIONS
__exidx_end = .;
} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
__rodata_region_start = .;
MMU_ALIGN;
__rodata_region_start = .;
#include <zephyr/linker/common-rom.ld>
/* Located in generated directory. This file is populated by calling
* zephyr_linker_sources(ROM_SECTIONS ...). Useful for grouping iterable RO structs.
*/
#include <snippets-rom-sections.ld>
#include <zephyr/linker/thread-local-storage.ld>
@ -184,9 +182,6 @@ SECTIONS
*(.got)
*(.got.plt)
/* Located in generated directory. This file is populated by the
* zephyr_linker_sources() Cmake function.
*/
#include <snippets-rodata.ld>
#include <zephyr/linker/kobject-rom.ld>
@ -194,8 +189,8 @@ SECTIONS
} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
#include <zephyr/linker/cplusplus-rom.ld>
MMU_ALIGN;
MMU_ALIGN;
__rodata_region_end = .;
__rodata_region_size = __rodata_region_end - __rodata_region_start;
__rom_region_end = .;
@ -214,19 +209,32 @@ SECTIONS
GROUP_START(RAMABLE_REGION)
#ifdef CONFIG_XIP
. = RAM_ADDR;
/* Align the start of image RAM with the
* minimum granularity required by MMU.
*/
. = ALIGN(_region_min_align);
#endif
MMU_ALIGN;
_image_ram_start = .;
#ifdef CONFIG_XIP
z_mapped_start = .;
#endif
/* Located in generated directory. This file is populated by the
* zephyr_linker_sources() Cmake function.
*/
__data_region_start = .;
SECTION_DATA_PROLOGUE(_DATA_SECTION_NAME,,)
{
MMU_ALIGN;
__data_start = .;
*(.data)
*(".data.*")
*(".kernel.*")
#include <snippets-rwdata.ld>
__data_end = .;
} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
__data_size = __data_end - __data_start;
__data_load_start = LOADADDR(_DATA_SECTION_NAME);
#include <snippets-ram-sections.ld>
#if defined(CONFIG_USERSPACE)
@ -249,6 +257,15 @@ SECTIONS
_app_smem_rom_start = LOADADDR(_APP_SMEM_SECTION_NAME);
#endif /* CONFIG_USERSPACE */
#include <zephyr/linker/common-ram.ld>
#include <zephyr/linker/kobject-data.ld>
#include <zephyr/linker/cplusplus-ram.ld>
#include <snippets-data-sections.ld>
__data_region_end = .;
__data_region_load_start = LOADADDR(_DATA_SECTION_NAME);
SECTION_DATA_PROLOGUE(_BSS_SECTION_NAME,(NOLOAD), BSS_ALIGN)
{
. = ALIGN(8);
@ -265,48 +282,10 @@ SECTIONS
#include <zephyr/linker/common-noinit.ld>
SECTION_DATA_PROLOGUE(_DATA_SECTION_NAME,,)
{
__data_region_start = .;
__data_start = .;
*(.data)
*(".data.*")
*(".kernel.*")
/* Located in generated directory. This file is populated by the
* zephyr_linker_sources() Cmake function.
*/
#include <snippets-rwdata.ld>
__data_end = .;
} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
__data_size = __data_end - __data_start;
__data_load_start = LOADADDR(_DATA_SECTION_NAME);
__data_region_load_start = LOADADDR(_DATA_SECTION_NAME);
#include <zephyr/linker/common-ram.ld>
#include <zephyr/linker/kobject-data.ld>
#include <zephyr/linker/cplusplus-ram.ld>
/* Located in generated directory. This file is populated by the
* zephyr_linker_sources() Cmake function.
*/
#include <snippets-data-sections.ld>
__data_region_end = .;
/* Define linker symbols */
__kernel_ram_end = RAM_ADDR + RAM_SIZE;
__kernel_ram_size = __kernel_ram_end - __kernel_ram_start;
/* Located in generated directory. This file is populated by the
* zephyr_linker_sources() Cmake function.
*/
#include <snippets-sections.ld>
#define LAST_RAM_ALIGN MMU_ALIGN;