Hi, On Sat, Feb 4, 2012 at 1:15 AM, Aneesh V <ane...@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: >> >> 1) 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. >> >> 2) 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 > > _______________________________________________ > U-Boot mailing list > U-Boot@lists.denx.de > http://lists.denx.de/mailman/listinfo/u-boot _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot