How to relcation .rodata with .text in Cortex-m3

Hi,

[Sorry, I am unable to answer you in Chinese.]

Dynamic linking requires an operating system and Cortex-M3 is typically used for bare-metal programming (ie no operating system).

As to your second question, as far as I know the boot up sequence is as follows:

1) device is reset
2) processor loads the address of the reset interrupt handler at address 0x4 and the base of the stack at address 0x0.
3) the processor execute the code of the interrupt handler at the address it just read

One thing to bear in mind is that the memory map for Cortex-M3 is as follows:

0x00000000 -> 0x1FFFFFFF flash
0x20000000 -> 0x3FFFFFFF RAM
0x40000000 -> 0x5FFFFFFF peripherals
0xE0000000 -> 0xFFFFFFFF system level addresses

The way it works is that you create a vector table (an array of pointers) in your code and put the base address of the stack and the address of the bootup code in the entries 0 and 1 of that table. The initialization of this table must be made statically as the table will be read before any code is executed. Then, use a linker script to put the vector table at the beginning of the .text section and the rest of the code after. You should also set the load address to be 0x0 and set the runtime address to a RAM address (for instance 0x20000000). Remember that the symbols in your code will resolve to the runtime address (ie if you do vector_table[1] = reset_handler it will use the runtime address of the reset_handler) but you need to write the load address of the reset handler because at first everything is in flash/ROM.

Then, when the device is turned on, the reset handler (your code whose address you put in the entry 1 of the vector table) is executed and it must copy everything (code and data) in RAM. Then you can call the main function and the program will execute. Note that typically all this is done by the boot code which you get from the manufacturer of the board.

You can find a bit more details at [1].

[1] http://markdingst.blogspot.co.uk/2012/06/make-own-bootloader-for-arm-cortex-m3.html

Hi Thomas,

Thanks for you solution!

I want to implement a Loader in the Cortex-m3 as one part of the operating system. So my Loader will boot up as you've said.

Now, I want my loader to loader other ELF file in the runtime. So I want to change the absolute address in the literal pool. I have do this after several weeks research. But there have still some problems.

Hi Thomas,

Thanks for you solution!

I want to implement a Loader in the Cortex-m3 as one part of the operating system. So my Loader will boot up as you've said.

Now, I want my loader to loader other ELF file in the runtime. So I want to change the absolute address in the literal pool. I have do this after several weeks research. But there have still some problems.