To make relocation on arm working, the following changes are done:
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At arch level: add linker flag -pie
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This causes the linker to generate fixup tables .rel.dyn and .dynsym,
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which must be applied to the relocated image before transferring
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control to it.
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These fixups are described in the ARM ELF documentation as type 23
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(program-base-relative) and 2 (symbol-relative)
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At cpu level: modify linker file and add a relocation and fixup loop
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the linker file must be modified to include the .rel.dyn and .dynsym
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tables in the binary image, and to provide symbols for the relocation
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code to access these tables
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The relocation and fixup loop must be executed after executing
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board_init_f at initial location and before executing board_init_r
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at final location.
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At board level:
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dram_init(): bd pointer is now at this point not accessible, so only
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detect the real dramsize, and store it in gd->ram_size. Bst detected
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with get_ram_size().
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TODO: move also dram initialization there on boards where it is possible.
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Setup of the the bd_t dram bank info is done in the new function
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dram_init_banksize() called after bd is accessible.
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At lib level:
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Board.c code is adapted from ppc code
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* WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING ** WARNING *
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Boards which are not fixed to support relocation will be REMOVED!
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-----------------------------------------------------------------------------
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For boards which boot from spl, it is possible to save one copy
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if CONFIG_SYS_TEXT_BASE == relocation address! This prevents that uboot code
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is copied again in relocate_code().
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example for the tx25 board booting from NAND Flash:
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a) cpu starts
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b) it copies the first page in nand to internal ram
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(spl code)
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c) end executes this code
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d) this initialize CPU, RAM, ... and copy itself to RAM
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(this bin must fit in one page, so board_init_f()
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don;t fit in it ... )
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e) there it copy u-boot to CONFIG_SYS_NAND_U_BOOT_DST and
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starts this image @ CONFIG_SYS_NAND_U_BOOT_START
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f) u-boot code steps through board_init_f() and calculates
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the relocation address and copy itself to it
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If CONFIG_SYS_TEXT_BASE == relocation address, the copying of u-boot
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in f) could be saved.
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-----------------------------------------------------------------------------
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TODO
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- fill in bd_t infos (check)
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- adapt all boards
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- maybe adapt CONFIG_SYS_TEXT_BASE (this must be checked from board maintainers)
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This *must* be done for boards, which boot from NOR flash
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on other boards if CONFIG_SYS_TEXT_BASE = relocation baseaddr, this saves
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one copying from u-boot code.
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- new function dram_init_banksize() is actual board specific. Maybe
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we make a weak default function in arch/arm/lib/board.c ?
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-----------------------------------------------------------------------------
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Relocation with SPL (example for the tx25 booting from NAND Flash):
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- cpu copies the first page from NAND to 0xbb000000 (IMX_NFC_BASE)
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and start with code execution on this address.
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- The First page contains u-boot code from drivers/mtd/nand/raw/mxc_nand_spl.c
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which inits the dram, cpu registers, reloacte itself to CONFIG_SPL_TEXT_BASE and loads
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the "real" u-boot to CONFIG_SYS_NAND_U_BOOT_DST and starts execution
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@CONFIG_SYS_NAND_U_BOOT_START
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- This u-boot does no RAM init, nor CPU register setup. Just look
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where it has to copy and relocate itself to this address. If
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relocate address = CONFIG_SYS_TEXT_BASE (not the same, as the
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CONFIG_SPL_TEXT_BASE from the spl code), then there is no need
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to copy, just go on with bss clear and jump to board_init_r.
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-----------------------------------------------------------------------------
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How ELF relocations 23 and 2 work.
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TBC
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-------------------------------------------------------------------------------------
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Debugging u-boot in RAM:
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(example on the qong board)
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-----------------
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a) start debugger
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arm-linux-gdb u-boot
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[hs@pollux u-boot]$ arm-linux-gdb u-boot
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GNU gdb Red Hat Linux (6.7-2rh)
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Copyright (C) 2007 Free Software Foundation, Inc.
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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This is free software: you are free to change and redistribute it.
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There is NO WARRANTY, to the extent permitted by law. Type "show copying"
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and "show warranty" for details.
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This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-linux".
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The target architecture is set automatically (currently arm)
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..
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(gdb)
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-----------------
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b) connect to target
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target remote bdi10:2001
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(gdb) target remote bdi10:2001
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Remote debugging using bdi10:2001
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0x8ff17f10 in ?? ()
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(gdb)
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-----------------
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c) discard symbol-file
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(gdb) symbol-file
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Discard symbol table from `/home/hs/celf/u-boot/u-boot'? (y or n) y
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No symbol file now.
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(gdb)
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-----------------
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d) load new symbol table:
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(gdb) add-symbol-file u-boot 0x8ff08000
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add symbol table from file "u-boot" at
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.text_addr = 0x8ff08000
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(y or n) y
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Reading symbols from /home/hs/celf/u-boot/u-boot...done.
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(gdb) c
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Continuing.
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^C
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Program received signal SIGSTOP, Stopped (signal).
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0x8ff17f18 in serial_getc () at serial_mxc.c:192
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192 while (__REG(UART_PHYS + UTS) & UTS_RXEMPTY);
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(gdb)
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add-symbol-file u-boot 0x8ff08000
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^^^^^^^^^^
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get this address from u-boot bdinfo command
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or get it from gd->relocaddr in gdb
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=> bdinfo
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rch_number = XXXXXXXXXX
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boot_params = XXXXXXXXXX
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DRAM bank = XXXXXXXXXX
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-> start = XXXXXXXXXX
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-> size = XXXXXXXXXX
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ethaddr = XXXXXXXXXX
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ip_addr = XXXXXXXXXX
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baudrate = XXXXXXXXXX
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TLB addr = XXXXXXXXXX
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relocaddr = 0x8ff08000
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^^^^^^^^^^
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reloc off = XXXXXXXXXX
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irq_sp = XXXXXXXXXX
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sp start = XXXXXXXXXX
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FB base = XXXXXXXXXX
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or interrupt execution by any means and re-load the symbols at the location
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specified by gd->relocaddr -- this is only valid after board_init_f.
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(gdb) set $s = gd->relocaddr
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(gdb) symbol-file
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(gdb) add-symbol-file u-boot $s
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Now you can use gdb as usual :-)
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