xref: /openbmc/u-boot/doc/README.arm-relocation (revision a1588ac8)

To make relocation on arm working, the following changes are done:

At arch level: add linker flag -pie

	This causes the linker to generate fixup tables .rel.dyn and .dynsym,
	which must be applied to the relocated image before transferring
	control to it.

	These fixups are described in the ARM ELF documentation as type 23
	(program-base-relative) and 2 (symbol-relative)

At cpu level: modify linker file and add a relocation and fixup loop

	the linker file must be modified to include the .rel.dyn and .dynsym
	tables in the binary image, and to provide symbols for the relocation
	code to access these tables

	The relocation and fixup loop must be executed after executing
	board_init_f at initial location and before executing board_init_r
	at final location.

At board level:

	dram_init(): bd pointer is now at this point not accessible, so only
	detect the real dramsize, and store it in gd->ram_size. Bst detected
	with get_ram_size().

TODO:	move also dram initialization there on boards where it is possible.

	Setup of the the bd_t dram bank info is done in the new function
	dram_init_banksize() called after bd is accessible.

At lib level:

	Board.c code is adapted from ppc code

* WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING *

Boards which are not fixed to support relocation will be REMOVED!

-----------------------------------------------------------------------------

For boards which boot from spl, it is possible to save one copy
if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code
is copied again in relocate_code().

example for the tx25 board booting from NAND Flash:

a) cpu starts
b) it copies the first page in nand to internal ram
   (spl code)
c) end executes this code
d) this initialize CPU, RAM, ... and copy itself to RAM
   (this bin must fit in one page, so board_init_f()
    don;t fit in it ... )
e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and
   starts this image @ CONFIG_SYS_NAND_U_BOOT_START
f) u-boot code steps through board_init_f() and calculates
   the relocation address and copy itself to it

If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot
in f) could be saved.

-----------------------------------------------------------------------------

TODO

- fill in bd_t infos (check)
- adapt all boards

- maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers)
  This *must* be done for boards, which boot from NOR flash

  on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves
  one copying from u-boot code.

- new function dram_init_banksize() is actual board specific. Maybe
  we make a weak default function in arch/arm/lib/board.c ?

-----------------------------------------------------------------------------

Relocation with SPL (example for the tx25 booting from NAND Flash):

- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
  and start with code execution on this address.

- The First page contains u-boot code from drivers/mtd/nand/raw/mxc_nand_spl.c
  which inits the dram, cpu registers, reloacte itself to CONFIG_SPL_TEXT_BASE	and loads
  the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
  @CONFIG_SYS_NAND_U_BOOT_START

- This u-boot does no RAM init, nor CPU register setup. Just look
  where it has to copy and relocate itself to this address. If
  relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the
  CONFIG_SPL_TEXT_BASE from the spl code), then there is no need
  to copy, just go on with bss clear and jump to board_init_r.

-----------------------------------------------------------------------------

How ELF relocations 23 and 2 work.

TBC

-------------------------------------------------------------------------------------

Debugging u-boot in RAM:
(example on the qong board)

-----------------

a) start debugger

arm-linux-gdb u-boot

[hs@pollux u-boot]$ arm-linux-gdb u-boot
GNU gdb Red Hat Linux (6.7-2rh)
Copyright (C) 2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
The target architecture is set automatically (currently arm)
..
(gdb)

-----------------

b) connect to target

target remote bdi10:2001

(gdb) target remote bdi10:2001
Remote debugging using bdi10:2001
0x8ff17f10 in ?? ()
(gdb)

-----------------

c) discard symbol-file

(gdb) symbol-file
Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
No symbol file now.
(gdb)

-----------------

d) load new symbol table:

(gdb) add-symbol-file u-boot 0x8ff08000
add symbol table from file "u-boot" at
	.text_addr = 0x8ff08000
(y or n) y
Reading symbols from /home/hs/celf/u-boot/u-boot...done.
(gdb) c
Continuing.
^C
Program received signal SIGSTOP, Stopped (signal).
0x8ff17f18 in serial_getc () at serial_mxc.c:192
192		while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
(gdb)

add-symbol-file u-boot 0x8ff08000
		       ^^^^^^^^^^
		       get this address from u-boot bdinfo command
		       or get it from gd->relocaddr in gdb

 => bdinfo
rch_number = XXXXXXXXXX
boot_params = XXXXXXXXXX
DRAM bank   = XXXXXXXXXX
-> start    = XXXXXXXXXX
-> size     = XXXXXXXXXX
ethaddr     = XXXXXXXXXX
ip_addr     = XXXXXXXXXX
baudrate    = XXXXXXXXXX
TLB addr    = XXXXXXXXXX
relocaddr   = 0x8ff08000
	      ^^^^^^^^^^
reloc off   = XXXXXXXXXX
irq_sp	    = XXXXXXXXXX
sp start    = XXXXXXXXXX
FB base     = XXXXXXXXXX

or interrupt execution by any means and re-load the symbols at the location
specified by gd->relocaddr -- this is only valid after board_init_f.

(gdb) set $s = gd->relocaddr
(gdb) symbol-file
(gdb) add-symbol-file u-boot $s

Now you can use gdb as usual :-)