To make relocation on arm working, the following changes are done: At arch level: add linker flag -pie This causes the linker to generate fixup tables .rel.dyn and .dynsym, which must be applied to the relocated image before transferring control to it. These fixups are described in the ARM ELF documentation as type 23 (program-base-relative) and 2 (symbol-relative) At cpu level: modify linker file and add a relocation and fixup loop the linker file must be modified to include the .rel.dyn and .dynsym tables in the binary image, and to provide symbols for the relocation code to access these tables The relocation and fixup loop must be executed after executing board_init_f at initial location and before executing board_init_r at final location. At board level: dram_init(): bd pointer is now at this point not accessible, so only detect the real dramsize, and store it in gd->ram_size. Bst detected with get_ram_size(). TODO: move also dram initialization there on boards where it is possible. Setup of the the bd_t dram bank info is done in the new function dram_init_banksize() called after bd is accessible. At lib level: Board.c code is adapted from ppc code * WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING * Boards which are not fixed to support relocation will be REMOVED! ----------------------------------------------------------------------------- For boards which boot from nand_spl, it is possible to save one copy if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code is copied again in relocate_code(). example for the tx25 board: a) cpu starts b) it copies the first page in nand to internal ram (nand_spl_code) c) end executes this code d) this initialize CPU, RAM, ... and copy itself to RAM (this bin must fit in one page, so board_init_f() don;t fit in it ... ) e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts this image @ CONFIG_SYS_NAND_U_BOOT_START f) u-boot code steps through board_init_f() and calculates the relocation address and copy itself to it If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot in f) could be saved. ----------------------------------------------------------------------------- TODO - fill in bd_t infos (check) - adapt all boards - maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers) This *must* be done for boards, which boot from NOR flash on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves one copying from u-boot code. - new function dram_init_banksize() is actual board specific. Maybe we make a weak default function in arch/arm/lib/board.c ? ----------------------------------------------------------------------------- Relocation with NAND_SPL (example for the tx25): - cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE) and start with code execution on this address. - The First page contains u-boot code from u-boot:nand_spl/nand_boot_fsl_nfc.c which inits the dram, cpu registers, reloacte itself to CONFIG_SYS_TEXT_BASE and loads the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution @CONFIG_SYS_NAND_U_BOOT_START - This u-boot does no RAM init, nor CPU register setup. Just look where it has to copy and relocate itself to this address. If relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the CONFIG_SYS_TEXT_BASE from the nand_spl code), then there is no need to copy, just go on with bss clear and jump to board_init_r. ----------------------------------------------------------------------------- How ELF relocations 23 and 2 work. TBC ------------------------------------------------------------------------------------- Debugging u-boot in RAM: (example on the qong board) a) add in config.mk: PLATFORM_CPPFLAGS += -DDEBUG ----------------- b) start debugger arm-linux-gdb u-boot [hs@pollux u-boot]$ arm-linux-gdb u-boot GNU gdb Red Hat Linux (6.7-2rh) Copyright (C) 2007 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux". The target architecture is set automatically (currently arm) .. (gdb) ----------------- c) connect to target target remote bdi10:2001 (gdb) target remote bdi10:2001 Remote debugging using bdi10:2001 0x8ff17f10 in ?? () (gdb) ----------------- d) discard symbol-file (gdb) symbol-file Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y No symbol file now. (gdb) ----------------- e) load new symbol table: (gdb) add-symbol-file u-boot 0x8ff08000 add symbol table from file "u-boot" at .text_addr = 0x8ff08000 (y or n) y Reading symbols from /home/hs/celf/u-boot/u-boot...done. (gdb) c Continuing. ^C Program received signal SIGSTOP, Stopped (signal). 0x8ff17f18 in serial_getc () at serial_mxc.c:192 192 while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY); (gdb) add-symbol-file u-boot 0x8ff08000 ^^^^^^^^^^ get this address from u-boot debug printfs U-Boot 2010.06-rc2-00009-gf77b8b8-dirty (Jun 22 2010 - 09:43:46) U-Boot code: A0000000 -> A0058BAC BSS: -> A0061F10 CPU: Freescale i.MX31 at 398 MHz Board: DAVE/DENX Qong mon: FFFFFFFF gd->monLen: 00061F10 Top of RAM usable for U-Boot at: 90000000 LCD panel info: 640 x 480, 16 bit/pix Reserving 600k for LCD Framebuffer at: 8ff6a000 Reserving 391k for U-Boot at: 8ff08000 ^^^^^^^^ Reserving 1280k for malloc() at: 8fdc8000 Reserving 24 Bytes for Board Info at: 8fdc7fe8 Reserving 52 Bytes for Global Data at: 8fdc7fb4 New Stack Pointer is: 8fdc7fb0 RAM Configuration: Bank #0: 80000000 256 MiB relocation Offset is: eff08000 mon: 00058BAC gd->monLen: 00061F10 Now running in RAM - U-Boot at: 8ff08000 ^^^^^^^^ Now you can use gdb as usual :-)