hi Darwin,
It's a little late.
> I'm hoping someone can help answer these questions about armv8 relocation.
>
> The CONFIG_SYS_TEXT_BASE seems to be be usually setup to a decent amount of
> alignment. For the purposes of this discussion, let's say it would normally
> be 0x88000000 and all is well. The relocation address moves to near the end
> of memory, to say, 0xfffa8000. So far so good.
>
> Now let's say I want to shift the image a bit so that I can add a small
> 32-byte header required by a previous bootloader. So I set
> CONFIG_SYS_TEXT_BASE to 0x88000020, and the relocated address is still
> 0xfffa8000 and the relocated vectors should be at 0xfffa9000. The image
> crashes so after some debugging, I find that the code appears to be relocated
> fine, but some sections have symbols that are not relocated properly. The
> vectors try to relocate to 0xfffa8fe0 and rodata.str1.1 printf format strings
> are also 0x20 off. There are likely other offset sections with issues as well.
>
> The relocation offset is 0x77fa7fe0 due to the calculations in
> arch/arm/lib/board.c. Simplifying, they look like this:
>
> addr = CONFIG_SYS_SDRAM_BASE + gd->ram_size;
>
> /* round down to next 4 kB limit */
> addr &= ~(4096 - 1);
> debug("Top of RAM usable for U-Boot at: %08lx\n", addr);
>
> /*
> * reserve memory for U-Boot code, data & bss
> * round down to next 4 kB limit
> */
> addr -= gd->mon_len;
> addr &= ~(4096 - 1);
>
> addr += 0x20; // hack to adjust relocaddr to aligned address...
>
> <snip>
>
> gd->relocaddr = addr;
> gd->start_addr_sp = addr_sp;
> gd->reloc_off = addr - _TEXT_BASE;
> debug("relocation Offset is: %08lx\n", gd->reloc_off);
>
>
> Since _TEXT_BASE is 0x88000020 and addr is 0xfffa8000, the reloc_off is a
> number like 0x77fa7fe0.
>
> Now if I add 0x20 to 'addr' above just before the <snip>, relocaddr becomes
> 0x77fa8000 and the relocation works perfectly and no more crashes happen.
>
> So my question - is the CONFIG_SYS_TEXT_BASE alignment requirement related to
> to any assumptions in the linker itself about image base alignment,
> specifically referring to creation of the rela.dyn sections and their use for
> image relocation?
>
> A related question is if CONFIG_SYS_TEXT_BASE needs to be at a specific
> alignment. The maximum alignment in the armv8 code base is ".align 11" which
> I believe means 0x800 or 2048.
>
> Note that an armv7 target appears to relocate properly with smaller offsets
> such as 0x20.
>
> Thanks.
>
>
I traced the problem you described and found it is caused by 'adrp'
instruction. 'adrp' instruction produces 4kb aligned address of a label. So, if
CONFIG_SYS_TEXT_BASE is not 4kb aligned the address produced by 'adrp' and
following 'add' instruction will be incorrect.
For example, if CONFIG_SYS_TEXT_BASE = 0x20 then address of '_start' is
0x20 and address of '_end_ofs' is 0x30, where u-boot access variable '_end_ofs'
gcc generate code as following:
adrp x0, ...
add x0, x0, 0x30
We noticed that 0x30 is added to 'x0' to produce the address of
'_end_ofs'. So when CONFIG_SYS_TEXT_BASE=0x20 and relocated destination address
is not 0x****020 register x0 contain incorrect address of '_end_ofs'.
David.
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
http://lists.denx.de/mailman/listinfo/u-boot
