ARM bootloader: the value of TEXT_BASE

Question

It's important to calculate correctly the value of TEXT_BASE when we begin to program the bootloader, but I haven't found a tutorial well explaining how to find this value according to platform datasheet or other materials. For example, for arm920t and sumsang s3c24x0, u-boot defines TEXT_BASE=0x33F80000 with this reason:

SMDK2410 has 1 bank of 64 MB DRAM
3000'0000 to 3400'0000
Linux-Kernel is expected to be at 3000'8000, entry 3000'8000 optionally with a ramdisk at 3080'0000
we load ourself to 33F8'0000
download area is 3300'0000

Can anyone explain the logic? Thanks!

ps: I also hope to know the memory layout of u-boot after load into the ram, the address of each data/instruction part, bss, rodata,zi, etc and the size. I expecte someone offer me some concerning tutorials to anaylyse, thank you!

Answer 1

TEXT_BASE is, unsurprisingly, the base address of the U-boot image i.e. where it starts executing from. So if U-boot is running straight from flash, it's the address of the flash. Or if ROM/firmware is responsible for loading U-boot then it's whatever address in RAM U-boot gets loaded to. Thus if you set TEXT_BASE to a different address it'll be linked wrong and will probably break at the relocation step.

As for the image layout, what's to ask? Either read the linker scripts, or just run a build then disassemble the u-boot ELF image that u-boot.bin is created from.