doc/README.arm-relocation

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

Add new compilerflag:

-fPIC

	-> compiler generates position independent code

changes in board code:

- dram_init:
  - bd pointer is now at this point not accessible, so only
    detect the real dramsize, and store it in gd->ram_size.
    best detected with get_ram_size();
    ToDo: move there also the dram initialization on boards where
          it is possible.
  - setup the bd_t dram bank info in the new function
    dram_init_banksize().

- board.c code is adapted from ppc code

- undef CONFIG_RELOC_FIXUP_WORKS

  -> cmdtabl, and subcommand table must be handled from "hand"
     collected in section "__datarellocal_start".

  - How To fixup the sections:

    __datarel_start, __datarelrolocal_start, __datarellocal_start and
    __datarelro_start

    automatically? Then it should be possible to define again
    CONFIG_RELOC_FIXUP_WORKS

- irq stack setup is now not longer on a fix position, instead it is
  calculated in board_init_f, and stored in gd->irq_sp

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

To compile a board without relocation, define CONFIG_SYS_ARM_WITHOUT_RELOC
This possibility will removed!! So please fix your board to compile without
CONFIG_SYS_ARM_WITHOUT_RELOC defined!!!

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

ToDo:

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

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

  on other boards if 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 NAND_SPL (example for the tx25):

- 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 u-boot:nand_spl/nand_boot_fsl_nfc.c
  which inits the dram, cpu registers, reloacte itself to 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 int, nor cpu register setup. Just looks
  where it have to relocate and relocate itself to this address.
  If relocate address = TEXT_BASE(not the same, as the TEXT_BASE
  from the nand_spl code), no need to copy, just go on with bss clear
  and jump to board_init_r.

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

Relocation:
How to translate flash addresses in GOT to ram addresses.
This is automagically done from code, but this example
shows, how this magic code works ;-)
(example on the qong board)

Find a variable:

a) search it in System.map
(for example flash_info)

a005b4c0 B BootpID
a005b4c4 B BootpTry
a005b4c8 b slave
a005b4cc B flash_info
^^^^^^^^
a005c908 b saved_sector.4002
a005c910 b cfi_mtd_info
a005c9c0 b cfi_mtd_names
a005c9d0 B mtd_table

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

b) create hexdump from u-boot code:

hexdump -C u-boot > gnlmpfhex

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

c) search the variables address in the hexdump


*
0005fc80  00 00 00 00 00 00 00 00  2c 06 01 a0 18 cd 05 a0  |........,.......|
0005fc90  9c d4 05 a0 bc b4 05 a0  1c 7f 05 a0 f0 05 01 a0  |................|
0005fca0  08 5a 04 a0 1c ab 05 a0  ec a4 05 a0 98 c3 01 a0  |.Z..............|
0005fcb0  a0 d6 05 a0 04 71 05 a0  c0 f9 00 a0 3c cd 05 a0  |.....q......<...|
0005fcc0  cc b4 05 a0 f0 fa 00 a0  f0 d6 05 a0 10 86 05 a0  |................|
          ^^^^^^^^^^^
0005fcd0  a4 16 06 a0 dc 64 05 a0  18 86 05 a0 52 48 05 a0  |.....d......RH..|
0005fce0  c0 86 05 a0 24 6e 02 a0  b4 6c 05 a0 b0 94 01 a0  |....$n...l......|
0005fcf0  1c 86 05 a0 50 85 05 a0  d4 0c 06 a0 bc 0b 06 a0  |....P...........|


-> 0005fcc0

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

d) know we calculate this address in RAM


  8ff08000	(new address of code in RAM *1)

+ 0005fcc0

- 00008000	(offset of text *2)

----------

  8ff5fcc0	-> Addr GOT in RAM

*1:
activate debug and look for the line:
Now running in RAM - U-Boot at: 8ff08000
                                ^^^^^^^^
                                new address of u-boot code in RAM

*2:
Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
  [ 1] .text             PROGBITS        a0000000 008000 04599c 00  AX  0   0 32
                                                  ^^^^^^
                                                  Offset of text

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

e) now we look in 8ff5fcc0 (RAM)


QongEVB>md 0x8ff5fcc0
8ff5fcc0 : a005b4cc a000faf0 a005d6f0 a0058610  ................
           ^^^^^^^^
           Bingo, here we have the old flash address (when relocation
           is working, here is the fixed ram address. see @ f, how
           it gets calculated)


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

f) now translate it in the new RAM address

  a005b4cc

- a0000000     TextBase

+ 8ff08000     new address of u-boot in ram
----------
  8ff634cc

QongEVB>mm 0x8ff5fcc0 0x8ff634cc 1
QongEVB>md 0x8ff5fcc0
8ff5fcc0 : 8ff634cc a000faf0 a005d6f0 a0058610  .4..............
8ff5fcd0 : a00616a4 a00564dc a0058618 a0054852  .....d......RH..

As this must be done for all address in the GOT, the u-boot
code did this automagically ... :-)

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

g) check if the new address is really in the bss section:

bss start:
8ff6054c	(8ff08000 + 0005854C monitorlen)

bss end:
8ff698ac	(8ff08000 + 618AC)

8ff634cc is in bss :-)

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

h) u-boot prints:

important  addresses:

U-Boot code: A0000000 -> A005854C  BSS: -> A00618AC	TextBase 0xa0000000
Now running in RAM - U-Boot at: 8ff08000		relocBase 0x8ff08000


---------

U-Boot 2010.06-rc2-00002-gf8fbb25-dirty (Jun 18 2010 - 17:07:19)

U-Boot code: A0000000 -> A005854C  BSS: -> A00618AC
CPU:   Freescale i.MX31 at 398 MHz
Board: DAVE/DENX Qong
mon: FFFFFFFF gd->monLen: 000618AC
Top of RAM usable for U-Boot at: 90000000
LCD panel info: 640 x 480, 16 bit/pix
Reserving 600k for LCD Framebuffer at: 8ff6a000
Reserving 390k for U-Boot at: 8ff08000
Reserving 1280k for malloc() at: 8fdc8000
Reserving 28 Bytes for Board Info at: 8fdc7fe4
Reserving 48 Bytes for Global Data at: 8fdc7fb4
New Stack Pointer is: 8fdc7fb0
RAM Configuration:
Bank #0: 80000000 256 MiB
mon: 0005854C gd->monLen: 000618AC
Now running in RAM - U-Boot at: 8ff08000

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

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

a) add in config.mk:

PLATFORM_CPPFLAGS += -DDEBUG

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

b) 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)

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

c) connect to target

target remote bdi10:2001

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

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

d) 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)

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

e) 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 debug printfs

U-Boot 2010.06-rc2-00009-gf77b8b8-dirty (Jun 22 2010 - 09:43:46)

U-Boot code: A0000000 -> A0058BAC  BSS: -> A0061F10
CPU:   Freescale i.MX31 at 398 MHz
Board: DAVE/DENX Qong
mon: FFFFFFFF gd->monLen: 00061F10
Top of RAM usable for U-Boot at: 90000000
LCD panel info: 640 x 480, 16 bit/pix
Reserving 600k for LCD Framebuffer at: 8ff6a000
Reserving 391k for U-Boot at: 8ff08000
                              ^^^^^^^^
Reserving 1280k for malloc() at: 8fdc8000
Reserving 24 Bytes for Board Info at: 8fdc7fe8
Reserving 52 Bytes for Global Data at: 8fdc7fb4
New Stack Pointer is: 8fdc7fb0
RAM Configuration:
Bank #0: 80000000 256 MiB
relocation Offset is: eff08000
mon: 00058BAC gd->monLen: 00061F10
Now running in RAM - U-Boot at: 8ff08000
                                ^^^^^^^^

Now you can use gdb as usual :-)