K 10
svn:author
V 6
luporl
K 8
svn:date
V 27
2019-10-31T11:59:00.314739Z
K 7
svn:log
V 540
[PPC64] Fix trapstk overflow

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

END