For now, distinguish alignment, translation and permission faults.
The first kind of faults cause the kernel to send SIGBUS to the
process causing the fault, the latter two are forwarded to `vm' as
pagefaults. Previously, any data abort was forwarded to `vm' as
a pagefault, resulting in hard to debug issue #104.
Any unhandled fault status results in a disaster. This seems
better than naively hoping `vm' can do something about it.
Change-Id: I526f575bb2681e087e20fd49c5c0846cdd450c31
For a reason currently unknown to us, the qemu-linaro emulator
sometimes produces a Prefetch Abort exception with a fault location
(IFAR) rather different from the location of the instruction being
executed (LR corrected by 4). So far it has been observed in the
__udivmodsi4 routine of various processes, where the fault address is
for the first byte of the next page after the current instruction,
which itself is 44-64 bytes away from the start of that next page.
The affected instruction does not perform any sort of memory access.
Short of debugging qemu-linaro itself, we have no choice but to
disable the assert that previously went off in case the IFAR and
corrected LR are not equal. Since we have not yet observed this case
on actual hardware, the kernel prints a warning when detecting such a
mismatch for the first time. For the qemu-linaro case, the kernel's
actual page fault handling logic already handles this strange case
just fine.
Change-Id: Ibd19e624149ab4e68bfe75b918ec1554b825a431
