UNIX V6 dump analysis

There are two kinds of dump analysis on UNIX V6, with some overlap between the two.

The first is of the core dump of an individual process into a file, created either by a user's request (typing '^\' in standard V6), or by any of the error conditions (odd address, etc) which cause a process abort.

The second is of a dump of the complete main memory of a PDP-11 running Unix; the system as distributed only supports doing such dumps to magnetic tape. This can be done either after the OS does a 'panic', which it does when something happens it can't recover from; or after halting the CPU.

Kernel stack top

For both process core dumps, and for system dumps after a panic, since all traps and interrupts come in through basically the same code, the base of the kernel stack will have the same format:

Offset	Contents
0	Old PS
2	Old PC
4	R0
6	New PS
10	R1
12	User SP
14	Index (trap type, device number)
16	R5
20	R4
22	R3
24	R2

The offset is from the top of the karnel stack, and is negative. In a process core dump, this starts at 01776 in the core dump file; in a dump of main memory, it is necessary to know the contents of kernel segment 6's address register, and the kernel stack top is 01776 above that.