xref: /openbmc/u-boot/doc/README.arm-relocation (revision 2e5167ccad93ca9cfa6a2acfab5e4785418e477e)
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	Undefine CONFIG_SYS_ARM_WITHOUT_RELOC
40
41* WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING *
42
43Boards which are not fixed to support relocation will be REMOVED!
44
45Eventually, CONFIG_SYS_ARM_WITHOUT_RELOC will disappear and boards
46which have to migrated to relocation will disappear too.
47
48-----------------------------------------------------------------------------
49
50For boards which boot from nand_spl, it is possible to save one copy
51if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code
52is copied again in relocate_code().
53
54example for the tx25 board:
55
56a) cpu starts
57b) it copies the first page in nand to internal ram
58   (nand_spl_code)
59c) end executes this code
60d) this initialize CPU, RAM, ... and copy itself to RAM
61   (this bin must fit in one page, so board_init_f()
62    don;t fit in it ... )
63e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and
64   starts this image @ CONFIG_SYS_NAND_U_BOOT_START
65f) u-boot code steps through board_init_f() and calculates
66   the relocation address and copy itself to it
67
68If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot
69in f) could be saved.
70
71-----------------------------------------------------------------------------
72
73TODO
74
75- fill in bd_t infos (check)
76- adapt all boards
77
78- maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers)
79  This *must* be done for boards, which boot from NOR flash
80
81  on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves
82  one copying from u-boot code.
83
84- new function dram_init_banksize() is actual board specific. Maybe
85  we make a weak default function in arch/arm/lib/board.c ?
86
87-----------------------------------------------------------------------------
88
89Relocation with NAND_SPL (example for the tx25):
90
91- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
92  and start with code execution on this address.
93
94- The First page contains u-boot code from u-boot:nand_spl/nand_boot_fsl_nfc.c
95  which inits the dram, cpu registers, reloacte itself to CONFIG_SYS_TEXT_BASE	and loads
96  the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
97  @CONFIG_SYS_NAND_U_BOOT_START
98
99- This u-boot does no RAM init, nor CPU register setup. Just look
100  where it has to copy and relocate itself to this address. If
101  relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the
102  CONFIG_SYS_TEXT_BASE from the nand_spl code), then there is no need
103  to copy, just go on with bss clear and jump to board_init_r.
104
105-----------------------------------------------------------------------------
106
107How ELF relocations 23 and 2 work.
108
109TBC
110
111-------------------------------------------------------------------------------------
112
113Debugging u-boot in RAM:
114(example on the qong board)
115
116a) add in config.mk:
117
118PLATFORM_CPPFLAGS += -DDEBUG
119
120-----------------
121
122b) start debugger
123
124arm-linux-gdb u-boot
125
126[hs@pollux u-boot]$ arm-linux-gdb u-boot
127GNU gdb Red Hat Linux (6.7-2rh)
128Copyright (C) 2007 Free Software Foundation, Inc.
129License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
130This is free software: you are free to change and redistribute it.
131There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
132and "show warranty" for details.
133This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
134The target architecture is set automatically (currently arm)
135..
136(gdb)
137
138-----------------
139
140c) connect to target
141
142target remote bdi10:2001
143
144(gdb) target remote bdi10:2001
145Remote debugging using bdi10:2001
1460x8ff17f10 in ?? ()
147(gdb)
148
149-----------------
150
151d) discard symbol-file
152
153(gdb) symbol-file
154Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
155No symbol file now.
156(gdb)
157
158-----------------
159
160e) load new symbol table:
161
162(gdb) add-symbol-file u-boot 0x8ff08000
163add symbol table from file "u-boot" at
164	.text_addr = 0x8ff08000
165(y or n) y
166Reading symbols from /home/hs/celf/u-boot/u-boot...done.
167(gdb) c
168Continuing.
169^C
170Program received signal SIGSTOP, Stopped (signal).
1710x8ff17f18 in serial_getc () at serial_mxc.c:192
172192		while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
173(gdb)
174
175add-symbol-file u-boot 0x8ff08000
176		       ^^^^^^^^^^
177		       get this address from u-boot debug printfs
178
179U-Boot 2010.06-rc2-00009-gf77b8b8-dirty (Jun 22 2010 - 09:43:46)
180
181U-Boot code: A0000000 -> A0058BAC  BSS: -> A0061F10
182CPU:   Freescale i.MX31 at 398 MHz
183Board: DAVE/DENX Qong
184mon: FFFFFFFF gd->monLen: 00061F10
185Top of RAM usable for U-Boot at: 90000000
186LCD panel info: 640 x 480, 16 bit/pix
187Reserving 600k for LCD Framebuffer at: 8ff6a000
188Reserving 391k for U-Boot at: 8ff08000
189			      ^^^^^^^^
190Reserving 1280k for malloc() at: 8fdc8000
191Reserving 24 Bytes for Board Info at: 8fdc7fe8
192Reserving 52 Bytes for Global Data at: 8fdc7fb4
193New Stack Pointer is: 8fdc7fb0
194RAM Configuration:
195Bank #0: 80000000 256 MiB
196relocation Offset is: eff08000
197mon: 00058BAC gd->monLen: 00061F10
198Now running in RAM - U-Boot at: 8ff08000
199				^^^^^^^^
200
201Now you can use gdb as usual :-)
202