I use a linker script to describe the memory map of my os kernel. In the linker script I defined many symbols to record location of section start/end. The linker script is as follow:
OUTPUT_FORMAT(binary)
SECTIONS {
/DISCARD/ : {
*(.comment)
*(.note.GNU-stack)
*(.eh_frame)
}
. = 0x100000;
kernel_load_addr = .;
.text : {
kernel_text_start = .;
*(.boot)
*(.text*)
kernel_text_end = .;
} = 0x90
.data : {
kernel_data_start = .;
*(.rodata*)
*(.data*)
kernel_data_end = .;
} = 0
.bss : {
kernel_bss_start = .;
*(COMMON)
*(.bss)
kernel_bss_end = .;
} = 0
kernel_end = .;
}
But if I print the address of these symbols out, the *_start symbol becomes same as *_end symbol.
I'm printing its value with following code:
extern char kernel_text_start;
extern char kernel_text_end;
extern char kernel_data_start;
extern char kernel_data_end;
extern char kernel_bss_start;
extern char kernel_bss_end;
...
raw_write(u64_to_str((uint64_t) &kernel_text_start, buf, 16), 0x0f, 0);
raw_write(u64_to_str((uint64_t) &kernel_text_end, buf, 16), 0x0f, 40);
raw_write(u64_to_str((uint64_t) &kernel_data_start, buf, 16), 0x0f, 80);
raw_write(u64_to_str((uint64_t) &kernel_data_end, buf, 16), 0x0f, 120);
raw_write(u64_to_str((uint64_t) &kernel_bss_start, buf, 16), 0x0f, 160);
raw_write(u64_to_str((uint64_t) &kernel_bss_end, buf, 16), 0x0f, 200);
and result is
The map file is:
Allocating common symbols
Common symbol size file
buddy_num 0x40 build/memory/page_alloc.c.o
buddy_map 0x40 build/memory/page_alloc.c.o
Discarded input sections
.comment 0x0000000000000000 0x4e build/kernel/main.c.o
.note.GNU-stack
0x0000000000000000 0x0 build/kernel/main.c.o
.eh_frame 0x0000000000000000 0x70 build/kernel/main.c.o
.comment 0x0000000000000000 0x4e build/memory/page_alloc.c.o
.note.GNU-stack
0x0000000000000000 0x0 build/memory/page_alloc.c.o
.eh_frame 0x0000000000000000 0xa8 build/memory/page_alloc.c.o
.comment 0x0000000000000000 0x4e build/memory/virt_alloc.c.o
.note.GNU-stack
0x0000000000000000 0x0 build/memory/virt_alloc.c.o
.comment 0x0000000000000000 0x4e build/library/bitmap.c.o
.note.GNU-stack
0x0000000000000000 0x0 build/library/bitmap.c.o
.eh_frame 0x0000000000000000 0x50 build/library/bitmap.c.o
.comment 0x0000000000000000 0x4e build/library/string.c.o
.note.GNU-stack
0x0000000000000000 0x0 build/library/string.c.o
.eh_frame 0x0000000000000000 0x150 build/library/string.c.o
Memory Configuration
Name Origin Length Attributes
*default* 0x0000000000000000 0xffffffffffffffff
Linker script and memory map
/DISCARD/
*(.comment)
*(.note.GNU-stack)
*(.eh_frame)
*(.comment)
*(.note.GNU-stack)
*(.eh_frame)
0x0000000000100000 . = 0x100000
0x0000000000100000 kernel_load_addr = .
0x0000000000100000 text_start_addr = .
.text 0x0000000000100000 0x262f
0x0000000000100000 kernel_text_start = .
*(.boot)
.boot 0x0000000000100000 0x29 build/boot/boot.asm.o
*(.text*)
*fill* 0x0000000000100029 0x7 90
.text 0x0000000000100030 0x0 build/boot/boot.asm.o
.text 0x0000000000100030 0x14f build/boot/init.asm.o
0x0000000000100030 wheel_init
*fill* 0x000000000010017f 0x1 90
.text 0x0000000000100180 0x73c build/kernel/main.c.o
0x0000000000100180 raw_write
0x0000000000100210 read_info
0x00000000001005e0 wheel_main
*fill* 0x00000000001008bc 0x4 90
.text 0x00000000001008c0 0x974 build/memory/page_alloc.c.o
0x00000000001008c0 page_alloc_init
0x0000000000100cb0 find_free_pages
0x0000000000100ef0 alloc_pages
0x00000000001010c0 free_pages
.text 0x0000000000101234 0x0 build/memory/virt_alloc.c.o
*fill* 0x0000000000101234 0xc 90
.text 0x0000000000101240 0x2ff build/library/bitmap.c.o
0x0000000000101240 bitmap_set
0x00000000001013c0 bitmap_clear
*fill* 0x000000000010153f 0x1 90
.text 0x0000000000101540 0x10ef build/library/string.c.o
0x0000000000101540 strlen
0x0000000000101650 strcpy
0x00000000001016c0 strncpy
0x0000000000101770 memcpy
0x0000000000101960 memset
0x0000000000101b60 u32_to_str
0x0000000000101c90 u64_to_str
0x0000000000101dd0 i32_to_str
0x0000000000101e60 i64_to_str
0x0000000000101ef0 vsprintf
0x00000000001025d0 sprintf
0x000000000010262f kernel_text_end = .
0x000000000010262f kernel_text_start = .
*(.boot)
*(.text*)
0x000000000010262f kernel_text_end = .
.data 0x0000000000102630 0x174
0x0000000000102630 kernel_data_start = .
*(.rodata*)
.rodata 0x0000000000102630 0x8 build/kernel/main.c.o
.rodata.str1.1
0x0000000000102638 0x82 build/kernel/main.c.o
*fill* 0x00000000001026ba 0x6 00000000
.rodata 0x00000000001026c0 0xa5 build/library/string.c.o
*(.data*)
*fill* 0x0000000000102765 0x3 00000000
.data 0x0000000000102768 0x3a build/boot/init.asm.o
*fill* 0x00000000001027a2 0x2 00000000
.data 0x00000000001027a4 0x0 build/kernel/main.c.o
.data 0x00000000001027a4 0x0 build/memory/page_alloc.c.o
.data 0x00000000001027a4 0x0 build/memory/virt_alloc.c.o
.data 0x00000000001027a4 0x0 build/library/bitmap.c.o
.data 0x00000000001027a4 0x0 build/library/string.c.o
0x00000000001027a4 kernel_data_end = .
0x00000000001027a4 kernel_data_start = .
*(.rodata*)
*(.data*)
0x00000000001027a4 kernel_data_end = .
0x00000000001027a4 data_end_addr = .
.bss 0x0000000000103000 0x6000
0x0000000000103000 kernel_bss_start = .
*(COMMON)
COMMON 0x0000000000103000 0x80 build/memory/page_alloc.c.o
0x0000000000103000 buddy_num
0x0000000000103040 buddy_map
*(.bss)
*fill* 0x0000000000103080 0xf80 00000000
.bss 0x0000000000104000 0x5000 build/boot/init.asm.o
0x0000000000104000 kernel_stack
0x0000000000105000 pml4t
.bss 0x0000000000109000 0x0 build/kernel/main.c.o
.bss 0x0000000000109000 0x0 build/memory/page_alloc.c.o
.bss 0x0000000000109000 0x0 build/memory/virt_alloc.c.o
.bss 0x0000000000109000 0x0 build/library/bitmap.c.o
.bss 0x0000000000109000 0x0 build/library/string.c.o
0x0000000000109000 kernel_bss_end = .
0x0000000000109000 kernel_bss_start = .
*(COMMON)
*(.bss)
0x0000000000109000 kernel_bss_end = .
0x0000000000109000 bss_end_addr = .
0x0000000000109000 kernel_end = .
LOAD build/boot/boot.asm.o
LOAD build/boot/init.asm.o
LOAD build/kernel/main.c.o
LOAD build/memory/page_alloc.c.o
LOAD build/memory/virt_alloc.c.o
LOAD build/library/bitmap.c.o
LOAD build/library/string.c.o
LOAD link.lds
0x0000000000100000 . = 0x100000
0x0000000000100000 kernel_load_addr = .
0x0000000000100000 text_start_addr = .
0x0000000000100000 data_end_addr = .
0x0000000000100000 bss_end_addr = .
0x0000000000100000 kernel_end = .
OUTPUT(build/kernel.bin binary)
You can see the value of these symbols got reassigned.
So how can I avoid this and get correct address in my program?