In some scenarios, the 4K trapstk may overflow, corrupting tmpstk.
This was observed during remote debugging, with the following steps:
At remote host (R):
- enter kdb during boot
- switch to gdb backend
At local host (L):
- attach gdb to R
- try to read an invalid memory position
At R:
- a DSI trap occurs and kdb restarts (all this occurs on trapstk)
- while printing the stacktrace, trapstk overflows and corrupts tmpstk
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D22200
1ac2596a4d