Hi Dirk,
On Friday 03 February 2012 12:55 PM, Dirk Behme wrote:
Hi,
on i.MX6 devices, e.g. ARM2 or SabreLite, the ROM boot loader copies the U-Boot image from the boot device, e.g. the SD card, to the main memory. This does mean that U-Boot is started in RAM.
With this, one might wonder why any relocation RAM -> RAM is done anyway and if this could be skipped?
Looking into the details shows that board_init_f() in arch/arm/lib/board.c and relocate_code() in arch/arm/cpu/armv7/start.S [1] are involved in this.
In board_init_f() the relocation destination address 'addr' is calculated. This is basically at the end of the available RAM (- some space for various stuff like TLB tables etc.). At SabreLite this results in 0x4FF8D000.
By the boot loader, the U-Boot is loaded to
CONFIG_SYS_TEXT_BASE 0x17800000
This results in relocate_code() copying U-Boot from RAM 0x17800000 to RAM 0x4FF8D000.
Setting CONFIG_SYS_TEXT_BASE to the relocation destination address 0x4FF8D000 does avoid the (unnecessary?) copy by
cmp r0, r6 moveq r9, #0 /* no relocation. relocation offset(r9) = 0 */ beq clear_bss /* skip relocation */
in relocate_code().
But:
- The resulting image still runs without the relocation
(CONFIG_SYS_TEXT_BASE 0x4FF8D000). But e.g. the U-Boot command line doesn't work properly any more. Most probably this is because not only the copy is skipped by the 'beq clear_bss', but the whole 'fix .rel.dyn relocations' is skipped too.
- It's hard to set CONFIG_SYS_TEXT_BASE at compile time to the
relocation address calculated at runtime in board_init_f() due to the amount of #ifdef and runtime calculation done there. So finding a generic approach which could easily defined in the config files to avoid the relocation seems difficult.
I haven't really completely read your mail. But here is an implementation I had provided long time back for ARM. But Wolfgang didn't want to take it. You can see the patch and the following discussion in this thread:
http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/96352
br, Aneesh