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Diffstat (limited to 'u-boot/doc/README.arm-relocation')
| -rw-r--r-- | u-boot/doc/README.arm-relocation | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/u-boot/doc/README.arm-relocation b/u-boot/doc/README.arm-relocation new file mode 100644 index 0000000..c0957c2 --- /dev/null +++ b/u-boot/doc/README.arm-relocation @@ -0,0 +1,194 @@ +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 :-) |