On 01.12.2009, at 19:33, Dima Ilyevsky wrote:
> Hello All,
>
> I have a question about read permissions of TBL SPR for all ppc processors:
> I have discovered that my application, compiled by WindRiver diab compiler
> and running in vxworks OS on ppc405 architecture bumps into exception
> generated when trying to read TBL or TBU registers:
Unless Linux does something funky, mftlb, mftbu (and mftb on 64 bit) are
readable from PR=1.
int main()
{
long tbu=0, tbl=0;
asm("mftbu %0" : "=r" (tbu));
asm("mftbl %0" : "=r" (tbl));
printf("TB: %#x %#x\n", tbl, tbu);
}
ag...@lychee:/tmp> ./mftb
TB: 0xc0397180 0x603
However it can't be written to:
asm("mttbl %0" : : "r" (tbl));
ag...@lychee:/tmp> ./mftb
Illegal instruction
So yes, I'd suspect a bug in qemu here. Feel free to send a patch.
Alex
