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/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