Re: unaligned accesses in apply_relocate_add

[Grant Grundler <grundler@parisc-linux.org>]

On Wed, Aug 26, 2009 at 04:41:20PM +0200, Artem Alimarine wrote:
> One point is that in the function apply_relocate_add a 4-byte aligned  
> address is created:
>
> 627                dot = (Elf64_Addr)loc & ~0x03;
> 628                loc64 = (Elf64_Xword *)loc;
>
> and used as a 64-bit location
>
> 711                case R_PARISC_DIR64:
> 712                        /* 64-bit effective address */
> 713                        *loc64 = val + addend;
> 714                        break;
>
> So, 8-byte word is read with a 4-byte alignment.

Perhaps this is expected to be an 8byte address pointing at a 4-byte word?
(and it's a bug that ist's not)

> I am busy building a parisc hardware emulator. It boots Linux, but it is  
> unstable yet. There are unaligned accesses in the emulation trace. I was  
> wandering whether it is normal behavior or caused by a bug in the  
> emulation.

HP has such an emulator. I've even tried to boot parisc-linux on it (failed)
~8 years ago.  Any chance someone from HP could publish it?

You might also look at Aries PA-RISC emulator (on ia64):
    http://www.princeton.edu/~rblee/ELE572Papers/PARISCtoIA64.htm

> The emulation trace gives a lot of accesses like this:
> 0-4011f968: translate_virtual_write unaligned_trap, va=0:416a20c  
> pa=1db1820c
> 0-4011f968: translate_virtual_write unaligned_trap, va=0:416a21c  
> pa=1db1821c
> 0-4011f968: translate_virtual_write unaligned_trap, va=0:416a224  
> pa=1db18224
>
> They are indeed 4-byte aligned. The PC address matches  
> apply_relocate_add in the kernel map.

*nod*

thanks,
grant