uboot/doc/README.arm-relocation
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   1To make relocation on arm working, the following changes are done:
   2
   3At arch level: add linker flag -pie
   4
   5        This causes the linker to generate fixup tables .rel.dyn and .dynsym,
   6        which must be applied to the relocated image before transferring
   7        control to it.
   8
   9        These fixups are described in the ARM ELF documentation as type 23
  10        (program-base-relative) and 2 (symbol-relative)
  11
  12At cpu level: modify linker file and add a relocation and fixup loop
  13
  14        the linker file must be modified to include the .rel.dyn and .dynsym
  15        tables in the binary image, and to provide symbols for the relocation
  16        code to access these tables
  17
  18        The relocation and fixup loop must be executed after executing
  19        board_init_f at initial location and before executing board_init_r
  20        at final location.
  21
  22At board level:
  23
  24        dram_init(): bd pointer is now at this point not accessible, so only
  25        detect the real dramsize, and store it in gd->ram_size. Bst detected
  26        with get_ram_size().
  27
  28TODO:   move also dram initialization there on boards where it is possible.
  29
  30        Setup of the the bd_t dram bank info is done in the new function
  31        dram_init_banksize() called after bd is accessible.
  32
  33At lib level:
  34
  35        Board.c code is adapted from ppc code
  36
  37* WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING *
  38
  39Boards which are not fixed to support relocation will be REMOVED!
  40
  41-----------------------------------------------------------------------------
  42
  43For boards which boot from spl, it is possible to save one copy
  44if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code
  45is copied again in relocate_code().
  46
  47example for the tx25 board booting from NAND Flash:
  48
  49a) cpu starts
  50b) it copies the first page in nand to internal ram
  51   (spl code)
  52c) end executes this code
  53d) this initialize CPU, RAM, ... and copy itself to RAM
  54   (this bin must fit in one page, so board_init_f()
  55    don;t fit in it ... )
  56e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and
  57   starts this image @ CONFIG_SYS_NAND_U_BOOT_START
  58f) u-boot code steps through board_init_f() and calculates
  59   the relocation address and copy itself to it
  60
  61If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot
  62in f) could be saved.
  63
  64-----------------------------------------------------------------------------
  65
  66TODO
  67
  68- fill in bd_t infos (check)
  69- adapt all boards
  70
  71- maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers)
  72  This *must* be done for boards, which boot from NOR flash
  73
  74  on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves
  75  one copying from u-boot code.
  76
  77- new function dram_init_banksize() is actual board specific. Maybe
  78  we make a weak default function in arch/arm/lib/board.c ?
  79
  80-----------------------------------------------------------------------------
  81
  82Relocation with SPL (example for the tx25 booting from NAND Flash):
  83
  84- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
  85  and start with code execution on this address.
  86
  87- The First page contains u-boot code from drivers/mtd/nand/mxc_nand_spl.c
  88  which inits the dram, cpu registers, reloacte itself to CONFIG_SPL_TEXT_BASE  and loads
  89  the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
  90  @CONFIG_SYS_NAND_U_BOOT_START
  91
  92- This u-boot does no RAM init, nor CPU register setup. Just look
  93  where it has to copy and relocate itself to this address. If
  94  relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the
  95  CONFIG_SPL_TEXT_BASE from the spl code), then there is no need
  96  to copy, just go on with bss clear and jump to board_init_r.
  97
  98-----------------------------------------------------------------------------
  99
 100How ELF relocations 23 and 2 work.
 101
 102TBC
 103
 104-------------------------------------------------------------------------------------
 105
 106Debugging u-boot in RAM:
 107(example on the qong board)
 108
 109-----------------
 110
 111a) start debugger
 112
 113arm-linux-gdb u-boot
 114
 115[hs@pollux u-boot]$ arm-linux-gdb u-boot
 116GNU gdb Red Hat Linux (6.7-2rh)
 117Copyright (C) 2007 Free Software Foundation, Inc.
 118License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 119This is free software: you are free to change and redistribute it.
 120There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
 121and "show warranty" for details.
 122This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
 123The target architecture is set automatically (currently arm)
 124..
 125(gdb)
 126
 127-----------------
 128
 129b) connect to target
 130
 131target remote bdi10:2001
 132
 133(gdb) target remote bdi10:2001
 134Remote debugging using bdi10:2001
 1350x8ff17f10 in ?? ()
 136(gdb)
 137
 138-----------------
 139
 140c) discard symbol-file
 141
 142(gdb) symbol-file
 143Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
 144No symbol file now.
 145(gdb)
 146
 147-----------------
 148
 149d) load new symbol table:
 150
 151(gdb) add-symbol-file u-boot 0x8ff08000
 152add symbol table from file "u-boot" at
 153        .text_addr = 0x8ff08000
 154(y or n) y
 155Reading symbols from /home/hs/celf/u-boot/u-boot...done.
 156(gdb) c
 157Continuing.
 158^C
 159Program received signal SIGSTOP, Stopped (signal).
 1600x8ff17f18 in serial_getc () at serial_mxc.c:192
 161192             while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
 162(gdb)
 163
 164add-symbol-file u-boot 0x8ff08000
 165                       ^^^^^^^^^^
 166                       get this address from u-boot bdinfo command
 167                       or get it from gd->relocaddr in gdb
 168
 169 => bdinfo
 170rch_number = XXXXXXXXXX
 171boot_params = XXXXXXXXXX
 172DRAM bank   = XXXXXXXXXX
 173-> start    = XXXXXXXXXX
 174-> size     = XXXXXXXXXX
 175ethaddr     = XXXXXXXXXX
 176ip_addr     = XXXXXXXXXX
 177baudrate    = XXXXXXXXXX
 178TLB addr    = XXXXXXXXXX
 179relocaddr   = 0x8ff08000
 180              ^^^^^^^^^^
 181reloc off   = XXXXXXXXXX
 182irq_sp      = XXXXXXXXXX
 183sp start    = XXXXXXXXXX
 184FB base     = XXXXXXXXXX
 185
 186or interrupt execution by any means and re-load the symbols at the location
 187specified by gd->relocaddr -- this is only valid after board_init_f.
 188
 189(gdb) set $s = gd->relocaddr
 190(gdb) symbol-file
 191(gdb) add-symbol-file u-boot $s
 192
 193Now you can use gdb as usual :-)
 194