xref: /openbmc/u-boot/doc/README.arm-relocation (revision f1d2b313c9eb6808d30c16a9eb5251240452a56c) 
1To make relocation on arm working, the following changes are done:
2
3Add new compilerflag:
4
5-fPIC
6
7	-> compiler generates position independent code
8
9changes in board code:
10
11- dram_init:
12  - bd pointer is now at this point not accessible, so only
13    detect the real dramsize, and store it in gd->ram_size.
14    best detected with get_ram_size();
15    ToDo: move there also the dram initialization on boards where
16          it is possible.
17  - setup the bd_t dram bank info in the new function
18    dram_init_banksize().
19
20- board.c code is adapted from ppc code
21
22- undef CONFIG_RELOC_FIXUP_WORKS
23
24  -> cmdtabl, and subcommand table must be handled from "hand"
25     collected in section "__datarellocal_start".
26
27  - How To fixup the sections:
28
29    __datarel_start, __datarelrolocal_start, __datarellocal_start and
30    __datarelro_start
31
32    automatically? Then it should be possible to define again
33    CONFIG_RELOC_FIXUP_WORKS
34
35- irq stack setup is now not longer on a fix position, instead it is
36  calculated in board_init_f, and stored in gd->irq_sp
37
38-------------------------------------------------------------------------------------
39
40To compile a board without relocation, define CONFIG_SYS_ARM_WITHOUT_RELOC
41This possibility will removed!! So please fix your board to compile without
42CONFIG_SYS_ARM_WITHOUT_RELOC defined!!!
43
44-------------------------------------------------------------------------------------
45
46ToDo:
47
48- fill in bd_t infos (check)
49- adapt all boards
50
51- maybe adapt TEXT_BASE (this must be checked from board maintainers)
52  This *must* be done for boards, which boot from NOR flash
53
54  on other boards if TEXT_BASE = relocation baseaddr, this saves
55  one copying from u-boot code.
56
57- new function dram_init_banksize() is actual board specific. Maybe
58  we make a weak default function in arch/arm/lib/board.c ?
59
60-------------------------------------------------------------------------------------
61
62Relocation with NAND_SPL (example for the tx25):
63
64- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
65  and start with code execution on this address.
66
67- The First page contains u-boot code from u-boot:nand_spl/nand_boot_fsl_nfc.c
68  which inits the dram, cpu registers, reloacte itself to TEXT_BASE  and loads
69  the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
70  @CONFIG_SYS_NAND_U_BOOT_START
71
72- This u-boot does no ram int, nor cpu register setup. Just looks
73  where it have to relocate and relocate itself to this address.
74  If relocate address = TEXT_BASE(not the same, as the TEXT_BASE
75  from the nand_spl code), no need to copy, just go on with bss clear
76  and jump to board_init_r.
77
78-------------------------------------------------------------------------------------
79
80Relocation:
81How to translate flash addresses in GOT to ram addresses.
82This is automagically done from code, but this example
83shows, how this magic code works ;-)
84(example on the qong board)
85
86Find a variable:
87
88a) search it in System.map
89(for example flash_info)
90
91a005b4c0 B BootpID
92a005b4c4 B BootpTry
93a005b4c8 b slave
94a005b4cc B flash_info
95^^^^^^^^
96a005c908 b saved_sector.4002
97a005c910 b cfi_mtd_info
98a005c9c0 b cfi_mtd_names
99a005c9d0 B mtd_table
100
101---------------------------------------
102
103b) create hexdump from u-boot code:
104
105hexdump -C u-boot > gnlmpfhex
106
107---------------------------------------
108
109c) search the variables address in the hexdump
110
111
112*
1130005fc80  00 00 00 00 00 00 00 00  2c 06 01 a0 18 cd 05 a0  |........,.......|
1140005fc90  9c d4 05 a0 bc b4 05 a0  1c 7f 05 a0 f0 05 01 a0  |................|
1150005fca0  08 5a 04 a0 1c ab 05 a0  ec a4 05 a0 98 c3 01 a0  |.Z..............|
1160005fcb0  a0 d6 05 a0 04 71 05 a0  c0 f9 00 a0 3c cd 05 a0  |.....q......<...|
1170005fcc0  cc b4 05 a0 f0 fa 00 a0  f0 d6 05 a0 10 86 05 a0  |................|
118          ^^^^^^^^^^^
1190005fcd0  a4 16 06 a0 dc 64 05 a0  18 86 05 a0 52 48 05 a0  |.....d......RH..|
1200005fce0  c0 86 05 a0 24 6e 02 a0  b4 6c 05 a0 b0 94 01 a0  |....$n...l......|
1210005fcf0  1c 86 05 a0 50 85 05 a0  d4 0c 06 a0 bc 0b 06 a0  |....P...........|
122
123
124-> 0005fcc0
125
126----------------------------------------
127
128d) know we calculate this address in RAM
129
130
131  8ff08000	(new address of code in RAM *1)
132
133+ 0005fcc0
134
135- 00008000	(offset of text *2)
136
137----------
138
139  8ff5fcc0	-> Addr GOT in RAM
140
141*1:
142activate debug and look for the line:
143Now running in RAM - U-Boot at: 8ff08000
144                                ^^^^^^^^
145                                new address of u-boot code in RAM
146
147*2:
148Section Headers:
149  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
150  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
151  [ 1] .text             PROGBITS        a0000000 008000 04599c 00  AX  0   0 32
152                                                  ^^^^^^
153                                                  Offset of text
154
155----------------------------------------
156
157e) now we look in 8ff5fcc0 (RAM)
158
159
160QongEVB>md 0x8ff5fcc0
1618ff5fcc0 : a005b4cc a000faf0 a005d6f0 a0058610  ................
162           ^^^^^^^^
163           Bingo, here we have the old flash address (when relocation
164           is working, here is the fixed ram address. see @ f, how
165           it gets calculated)
166
167
168----------------------------------------
169
170f) now translate it in the new RAM address
171
172  a005b4cc
173
174- a0000000     TextBase
175
176+ 8ff08000     new address of u-boot in ram
177----------
178  8ff634cc
179
180QongEVB>mm 0x8ff5fcc0 0x8ff634cc 1
181QongEVB>md 0x8ff5fcc0
1828ff5fcc0 : 8ff634cc a000faf0 a005d6f0 a0058610  .4..............
1838ff5fcd0 : a00616a4 a00564dc a0058618 a0054852  .....d......RH..
184
185As this must be done for all address in the GOT, the u-boot
186code did this automagically ... :-)
187
188----------------------------------------------
189
190g) check if the new address is really in the bss section:
191
192bss start:
1938ff6054c	(8ff08000 + 0005854C monitorlen)
194
195bss end:
1968ff698ac	(8ff08000 + 618AC)
197
1988ff634cc is in bss :-)
199
200----------------------------------------------
201
202h) u-boot prints:
203
204important  addresses:
205
206U-Boot code: A0000000 -> A005854C  BSS: -> A00618AC	TextBase 0xa0000000
207Now running in RAM - U-Boot at: 8ff08000		relocBase 0x8ff08000
208
209
210---------
211
212U-Boot 2010.06-rc2-00002-gf8fbb25-dirty (Jun 18 2010 - 17:07:19)
213
214U-Boot code: A0000000 -> A005854C  BSS: -> A00618AC
215CPU:   Freescale i.MX31 at 398 MHz
216Board: DAVE/DENX Qong
217mon: FFFFFFFF gd->monLen: 000618AC
218Top of RAM usable for U-Boot at: 90000000
219LCD panel info: 640 x 480, 16 bit/pix
220Reserving 600k for LCD Framebuffer at: 8ff6a000
221Reserving 390k for U-Boot at: 8ff08000
222Reserving 1280k for malloc() at: 8fdc8000
223Reserving 28 Bytes for Board Info at: 8fdc7fe4
224Reserving 48 Bytes for Global Data at: 8fdc7fb4
225New Stack Pointer is: 8fdc7fb0
226RAM Configuration:
227Bank #0: 80000000 256 MiB
228mon: 0005854C gd->monLen: 000618AC
229Now running in RAM - U-Boot at: 8ff08000
230
231-------------------------------------------------------------------------------------
232
233Debugging u-boot in RAM:
234(example on the qong board)
235
236a) add in config.mk:
237
238PLATFORM_CPPFLAGS += -DDEBUG
239
240-----------------
241
242b) start debugger
243
244arm-linux-gdb u-boot
245
246[hs@pollux u-boot]$ arm-linux-gdb u-boot
247GNU gdb Red Hat Linux (6.7-2rh)
248Copyright (C) 2007 Free Software Foundation, Inc.
249License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
250This is free software: you are free to change and redistribute it.
251There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
252and "show warranty" for details.
253This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
254The target architecture is set automatically (currently arm)
255..
256(gdb)
257
258-----------------
259
260c) connect to target
261
262target remote bdi10:2001
263
264(gdb) target remote bdi10:2001
265Remote debugging using bdi10:2001
2660x8ff17f10 in ?? ()
267(gdb)
268
269-----------------
270
271d) discard symbol-file
272
273(gdb) symbol-file
274Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
275No symbol file now.
276(gdb)
277
278-----------------
279
280e) load new symbol table:
281
282(gdb) add-symbol-file u-boot 0x8ff08000
283add symbol table from file "u-boot" at
284        .text_addr = 0x8ff08000
285(y or n) y
286Reading symbols from /home/hs/celf/u-boot/u-boot...done.
287(gdb) c
288Continuing.
289^C
290Program received signal SIGSTOP, Stopped (signal).
2910x8ff17f18 in serial_getc () at serial_mxc.c:192
292192             while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
293(gdb)
294
295add-symbol-file u-boot 0x8ff08000
296                       ^^^^^^^^^^
297                       get this address from u-boot debug printfs
298
299U-Boot 2010.06-rc2-00009-gf77b8b8-dirty (Jun 22 2010 - 09:43:46)
300
301U-Boot code: A0000000 -> A0058BAC  BSS: -> A0061F10
302CPU:   Freescale i.MX31 at 398 MHz
303Board: DAVE/DENX Qong
304mon: FFFFFFFF gd->monLen: 00061F10
305Top of RAM usable for U-Boot at: 90000000
306LCD panel info: 640 x 480, 16 bit/pix
307Reserving 600k for LCD Framebuffer at: 8ff6a000
308Reserving 391k for U-Boot at: 8ff08000
309                              ^^^^^^^^
310Reserving 1280k for malloc() at: 8fdc8000
311Reserving 24 Bytes for Board Info at: 8fdc7fe8
312Reserving 52 Bytes for Global Data at: 8fdc7fb4
313New Stack Pointer is: 8fdc7fb0
314RAM Configuration:
315Bank #0: 80000000 256 MiB
316relocation Offset is: eff08000
317mon: 00058BAC gd->monLen: 00061F10
318Now running in RAM - U-Boot at: 8ff08000
319                                ^^^^^^^^
320
321Now you can use gdb as usual :-)
322