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 bd_info 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 struct bd_info 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/raw/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