如何将二进制文件构建到固定地址 0x80000 的图像中？

Question

In our c project, we need to build a binary firmware into a image at a fixed file offset 0x80000.

Then when the image is loaded to memory. We can load firmware from offset 0x80000 to a specified address. Meanwhile, as the firmware is placed at file offset 0x80000, we can upgrade the firmare independently.

So I'm trying to use GNU linker script to implement that. What I do now is use incbin to include my binary file in a asm file. And in linker script, my code is:

       .fw_image_start : {
                *(.__fw_image_start)
        }

       .fw_image : {
              KEEP(*(.fw_image))
        }

       .fw_image_end : {
                *(.__fw_image_end)
        }

Then I can use fw_image_start to load firmware in image code.

But I still can't find a way to put the firmware binary to file offset 0x80000 in the final image.

Could you help me on this?

Thank you in advance!

Answer 1

What did you find when you looked at the documentation and examples from GNU? Some of it is admittedly confusing or misleading, but some is pretty easy. This should give a hit of at least one way to do it (there are multiple ways to solve your problem).

novectors.s

.global _start
_start:
    bl notmain
    b .

.globl bounce
bounce:
    bx lr

.section .hello_world
.word 1,2,3,4

notmain.c

void bounce ( unsigned int );
unsigned int mybss[8];
int notmain ( void )
{
    unsigned int ra;

    for(ra=0;ra<1000;ra++) bounce(ra);

    return(0);
}

memmap.ld

MEMORY
{
    ram : ORIGIN = 0x80000, LENGTH = 0x1000
}
SECTIONS
{
    .text : { *(.text*) } > ram
    .rodata : { *(.rodata*) } > ram
    .hello_world : { *(.hello_world) } > ram
    .bss : { *(.bss*) } > ram
}

build

arm-none-eabi-as --warn --fatal-warnings  novectors.s -o novectors.o
arm-none-eabi-gcc -Wall -Werror -O2 -nostdlib -nostartfiles -ffreestanding -c notmain.c -o notmain.o
arm-none-eabi-ld -o notmain.elf -T memmap.ld novectors.o notmain.o
arm-none-eabi-objdump -D notmain.elf > notmain.list
arm-none-eabi-objcopy notmain.elf notmain.bin -O binary

examine results

Disassembly of section .text:

00080000 <_start>:
   80000:   eb000001    bl  8000c <notmain>
   80004:   eafffffe    b   80004 <_start+0x4>

00080008 <bounce>:
   80008:   e12fff1e    bx  lr

0008000c <notmain>:
   8000c:   e92d4010    push    {r4, lr}
   80010:   e3a04000    mov r4, #0
   80014:   e1a00004    mov r0, r4
   80018:   e2844001    add r4, r4, #1
   8001c:   ebfffff9    bl  80008 <bounce>
   80020:   e3540ffa    cmp r4, #1000   ; 0x3e8
   80024:   1afffffa    bne 80014 <notmain+0x8>
   80028:   e3a00000    mov r0, #0
   8002c:   e8bd4010    pop {r4, lr}
   80030:   e12fff1e    bx  lr

Disassembly of section .hello_world:

00080034 <.hello_world>:
   80034:   00000001    andeq   r0, r0, r1
   80038:   00000002    andeq   r0, r0, r2
   8003c:   00000003    andeq   r0, r0, r3
   80040:   00000004    andeq   r0, r0, r4

Disassembly of section .bss:

00080034 <mybss>:
    ...

Naturally:

MEMORY
{
    bob : ORIGIN = 0x80000, LENGTH = 0x1000
    ted : ORIGIN = 0xB0000, LENGTH = 0x1000
}
SECTIONS
{
    .text : { *(.text*) } > bob
    .rodata : { *(.rodata*) } > bob
    .hello_world : { *(.hello_world) } > ted
    .bss : { *(.bss*) } > ted
}

gives

Disassembly of section .text:

00080000 <_start>:
   80000:   eb000001    bl  8000c <notmain>
   80004:   eafffffe    b   80004 <_start+0x4>

00080008 <bounce>:
   80008:   e12fff1e    bx  lr

0008000c <notmain>:
   8000c:   e92d4010    push    {r4, lr}
   80010:   e3a04000    mov r4, #0
   80014:   e1a00004    mov r0, r4
   80018:   e2844001    add r4, r4, #1
   8001c:   ebfffff9    bl  80008 <bounce>
   80020:   e3540ffa    cmp r4, #1000   ; 0x3e8
   80024:   1afffffa    bne 80014 <notmain+0x8>
   80028:   e3a00000    mov r0, #0
   8002c:   e8bd4010    pop {r4, lr}
   80030:   e12fff1e    bx  lr

Disassembly of section .hello_world:

000b0000 <.hello_world>:
   b0000:   00000001    andeq   r0, r0, r1
   b0004:   00000002    andeq   r0, r0, r2
   b0008:   00000003    andeq   r0, r0, r3
   b000c:   00000004    andeq   r0, r0, r4

Disassembly of section .bss:

000b0000 <mybss>:
    ...

and as demonstrated the name ram, rom, etc are not special can call it other things like bob, ted, alice...I assume there are some reserved words you cant use.

Again there are numerous solutions, see the GNU documentation, I like this method as it reads better for me, but you will see solutions that skip the MEMORY part.

(no this wasnt intended to be completely correct code, but demonstrates the assembly language bootstrap, the C code and the linker script).