On Thu, 20 Apr 2023, Michael Schmitz wrote:
Am 20.04.2023 um 17:17 schrieb Finn Thain:
On Thu, 20 Apr 2023, Michael Schmitz wrote:
As with dash, the corruption lies the page boundary.
Hence implies a page fault handled at the page boundary.
Can you try and fault in as many of these stack pages as possible, ahead
of filling the stack? (Depending on how much RAM you have ...). Maybe we
would need to lock those pages into memory? Just to show that with no
page faults (but still signals) there is no corruption?
I modified the test program to execute rec() to full depth with no
forking, then do it again with forking.
root@(none):/root# while ./stack-test 5000 ; do : ; done
starting recursion
done.
starting recursion with fork
done.
starting recursion
done.
starting recursion with fork
Illegal instruction
root@(none):/root#
I can't get this to crash during the first descent. The second descent
always crashes, given sufficient depth:
root@(none):/root# while ./stack-test 50000 ; do : ; done
starting recursion
done.
starting recursion with fork
Illegal instruction
So all the stack pages would have been faulted in well before the
failure shows up. It appears to be the signal that's the problem and
not the page fault. That's not surprising considering the PC in the
signal frame in the dash crash was a MOVEM saving registers onto the
stack.
Well. without locking the faulted in pages in memory we can't be sure
they were not swapped back out. Unless I misunderstand what's involved
in that ...
There was no swap enabled.
50000 frames * 36 bytes per frame == 1.8 MB
