From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aneesh V Date: Sat, 04 Feb 2012 16:44:57 +0530 Subject: [U-Boot] Skipping relocation RAM to RAM, esp. on i.MX6? In-Reply-To: <4F2D0FE7.8020107@aribaud.net> References: <4F2B8BD1.2030009@de.bosch.com> <4F2CF73F.2090407@ti.com> <4F2D0FE7.8020107@aribaud.net> Message-ID: <4F2D1331.2060406@ti.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On Saturday 04 February 2012 04:30 PM, Albert ARIBAUD wrote: > Le 04/02/2012 10:15, Aneesh V a ?crit : >> 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 > > Recently there was an reminder by Wolfgang that debugging can be done > even with relocation, provided the symbols are dropped and reloaded in > gdb upon hitting the end of the relocate loop where the jump to (the new > location of) board_init_f happens --see > . > > I am not a specialist of gdb but I think it might be automated, too, so > that if you want to debug u-boot past relocation then you would just > have to enter a single command in gdb, or a script name when invoking > gdb, to load u-boot in low RAM , set a breakpoint at the pivot point > after relocation, run to that breakpoint, drop current symbols and > reload symbols with the adequate offset, possibly computed from some > accessible global. > > Anyone itching enough to do some research and experiments on this? I employ a different method using my JTAG debugger. 1. Look at the content of gd using the address from r8. Lauterbach allows you to cast that address to a (struct global_data *) and view the contents. 2. Get reloc_off from gd and use that to relocate the symbols in Trace32. The advantage is that I can do all this after booting completely. No breakpoint needed. br, Aneesh