Hi,
On Sat, Feb 4, 2012 at 1:15 AM, Aneesh V aneesh@ti.com wrote:
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
From your patch Aneesh I evolved something that I still use - it deals
with the case where malloc cannot fit below the text area.
I find any sort of messing with the ICE startup a pain - although I have often been able to script it. But for me I need to attach the device tree to the binary and a few other things so I might as well disable relocation at the same time. It also allows me to debug seamlessly in board_init_f() as well as afterwards.
I will send a patch.
It would be good to get something in mainline despite the protestations, if only to avoid all the work that people have to do to figure out this problem.
Regards, Simon
br, Aneesh
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