xref: /openbmc/u-boot/doc/README.arm-relocation (revision 071bc923308832bbc541a887fece767d79a6dc7a)
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
37At config level:
38
39	Define CONFIG_RELOC_FIXUP_WORKS.
40	Undefine CONFIG_SYS_ARM_WITHOUT_RELOC
41
42* WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING *
43
44Boards which are not fixed to support relocation will be REMOVED!
45
46Eventually, CONFIG_SYS_ARM_WITHOUT_RELOC and CONFIG_RELOC_FIXUP_WORKS will
47disappear and boards which have to migrated to relocation will disappear too.
48
49-----------------------------------------------------------------------------
50
51For boards which boot from nand_spl, it is possible to save one copy
52if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code
53is copied again in relocate_code().
54
55example for the tx25 board:
56
57a) cpu starts
58b) it copies the first page in nand to internal ram
59   (nand_spl_code)
60c) end executes this code
61d) this initialize CPU, RAM, ... and copy itself to RAM
62   (this bin must fit in one page, so board_init_f()
63    don;t fit in it ... )
64e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and
65   starts this image @ CONFIG_SYS_NAND_U_BOOT_START
66f) u-boot code steps through board_init_f() and calculates
67   the relocation address and copy itself to it
68
69If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot
70in f) could be saved.
71
72-----------------------------------------------------------------------------
73
74TODO
75
76- fill in bd_t infos (check)
77- adapt all boards
78
79- maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers)
80  This *must* be done for boards, which boot from NOR flash
81
82  on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves
83  one copying from u-boot code.
84
85- new function dram_init_banksize() is actual board specific. Maybe
86  we make a weak default function in arch/arm/lib/board.c ?
87
88-----------------------------------------------------------------------------
89
90Relocation with NAND_SPL (example for the tx25):
91
92- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
93  and start with code execution on this address.
94
95- The First page contains u-boot code from u-boot:nand_spl/nand_boot_fsl_nfc.c
96  which inits the dram, cpu registers, reloacte itself to CONFIG_SYS_TEXT_BASE	and loads
97  the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
98  @CONFIG_SYS_NAND_U_BOOT_START
99
100- This u-boot does no RAM init, nor CPU register setup. Just look
101  where it has to copy and relocate itself to this address. If
102  relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the
103  CONFIG_SYS_TEXT_BASE from the nand_spl code), then there is no need
104  to copy, just go on with bss clear and jump to board_init_r.
105
106-----------------------------------------------------------------------------
107
108How ELF relocations 23 and 2 work.
109
110TBC
111
112-------------------------------------------------------------------------------------
113
114Debugging u-boot in RAM:
115(example on the qong board)
116
117a) add in config.mk:
118
119PLATFORM_CPPFLAGS += -DDEBUG
120
121-----------------
122
123b) start debugger
124
125arm-linux-gdb u-boot
126
127[hs@pollux u-boot]$ arm-linux-gdb u-boot
128GNU gdb Red Hat Linux (6.7-2rh)
129Copyright (C) 2007 Free Software Foundation, Inc.
130License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
131This is free software: you are free to change and redistribute it.
132There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
133and "show warranty" for details.
134This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
135The target architecture is set automatically (currently arm)
136..
137(gdb)
138
139-----------------
140
141c) connect to target
142
143target remote bdi10:2001
144
145(gdb) target remote bdi10:2001
146Remote debugging using bdi10:2001
1470x8ff17f10 in ?? ()
148(gdb)
149
150-----------------
151
152d) discard symbol-file
153
154(gdb) symbol-file
155Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
156No symbol file now.
157(gdb)
158
159-----------------
160
161e) load new symbol table:
162
163(gdb) add-symbol-file u-boot 0x8ff08000
164add symbol table from file "u-boot" at
165	.text_addr = 0x8ff08000
166(y or n) y
167Reading symbols from /home/hs/celf/u-boot/u-boot...done.
168(gdb) c
169Continuing.
170^C
171Program received signal SIGSTOP, Stopped (signal).
1720x8ff17f18 in serial_getc () at serial_mxc.c:192
173192		while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
174(gdb)
175
176add-symbol-file u-boot 0x8ff08000
177		       ^^^^^^^^^^
178		       get this address from u-boot debug printfs
179
180U-Boot 2010.06-rc2-00009-gf77b8b8-dirty (Jun 22 2010 - 09:43:46)
181
182U-Boot code: A0000000 -> A0058BAC  BSS: -> A0061F10
183CPU:   Freescale i.MX31 at 398 MHz
184Board: DAVE/DENX Qong
185mon: FFFFFFFF gd->monLen: 00061F10
186Top of RAM usable for U-Boot at: 90000000
187LCD panel info: 640 x 480, 16 bit/pix
188Reserving 600k for LCD Framebuffer at: 8ff6a000
189Reserving 391k for U-Boot at: 8ff08000
190			      ^^^^^^^^
191Reserving 1280k for malloc() at: 8fdc8000
192Reserving 24 Bytes for Board Info at: 8fdc7fe8
193Reserving 52 Bytes for Global Data at: 8fdc7fb4
194New Stack Pointer is: 8fdc7fb0
195RAM Configuration:
196Bank #0: 80000000 256 MiB
197relocation Offset is: eff08000
198mon: 00058BAC gd->monLen: 00061F10
199Now running in RAM - U-Boot at: 8ff08000
200				^^^^^^^^
201
202Now you can use gdb as usual :-)
203