ANALYZE(1M)

NAME
analyze - Virtual UNIX postmortem crash analyzer

SYNOPSIS
analyze [ -s swapfile ] [ -fmdDv ] corefile [ system ]

DESCRIPTION
Analyze is the post-mortem analyzer for the state of the paging system. The following procedure should be followed when the paging system crashes:

1)  Following normal crash dump procedures, dump the PSL, registers and the top 40 or so locations of the kernel stack on the console, and then take a core image dump on tape.

2)  Boot a version of the system which pages or swaps in an area distinct from the paging system.

3)  Fix the root file system and then copy the mag tape into the file /vmcore (cp will do fine).

4)  Run the command ``analyze -s /dev/drum /vmcore /vmunix'' and save the output for a systems programmer.

5)  Follow the normal reboot procedure to resume operations.

6)  When the system is up again, run the command ``pstat -pxk /vmcore /vmunix'' and route the output to a hardcopy device.

The outputs from the above procedure will get you started investigating the cause of the crash, if it was paging related. For details on the internal data structures of the system see the document Data Structures added in the Berkeley Virtual Memory Extensions to the UNIX System A listing of the system will also be handy while examining the core dump. It is suggested that you save the file /vmcore in a less volatile place if you want to make sure it is not clobbered.

The analyze program reads the relevant system data structures from the core image file and coordinates these with the information on the disk to determine the state of the paging subsystem at the point of crash. It looks at each process in the system, and the resources each is using in an attempt to determine inconsistencies in the paging system state. Normally, the output consists of a sequence of lines showing each active process, its state (whether swapped in or not), its p0br, and the number and location of its page table pages. Any pages which are locked while raw i/o is in progress, or which are locked because they are intransit are also printed. (Intransit text pages often diagnose as duplicated; you will have to weed these out by hand.)

The program checks that any pages in core which are marked as not modified are, in fact, identical to the swap space copies. It also checks for non-overlap of the swap space, and that the core map entries correspond to the page tables. The state of the free list is also checked.

Options to analyze include -m which causes the entire coremap state to be dumped, -D which causes the diskmap for each process to be printed, -d which causes the (sorted) paging area usage to be printed, -v (long unused) which causes a hugely verbose output format to be used, and -f which causes the free list to be dumped.

In general, the output from this program can be confused by processes which were forking, swapping, or exiting or happened to be in unusual states when the crash occurred. You should examine the flags field of the output of pstat to help filter out such processes.

You can look at the core dump with adb if you do

    adb /vmunix /vmcore
    /m 80000000 #ffffffff

which fixes the map of vmcore so that symbols in data space will work. It will be necessary to do

    ?m 80000000 #ffffffff

to get text symbols to work also. You can then look at the Umap array to see the u. pages of the process which was running at the point of the crash. Find the first number in the output of pstat. You should be able to find the kernel stack at the point of crash either as the stack in the u. area for this process or in the interrupt stack intstack.

Note that the debugger is looking at the physical memory at the point of crash; you will have to determine which pages of physical memory the stack is in if you wish to look at it by computing 0x80000000 + Umap[i] * 0x200. A similar computation will give addresses of page table pages. Thus if analyze says that a processes page tables are in page 218 (hex of course), then you can look at them by looking at address 0x80043000 in the dump, i.e. ``80043000,80/X'' will print the page of page tables.

FILES
/vmunix    default system namelist

SEE ALSO
``Data Structures added in the Berkeley Virtual Memory Extensions to the UNIX System'', crash(8), pstat(1m), ps(1)

AUTHORS
Ozalp Babaoglu and William Joy

DIAGNOSTICS
Various diagnostics about overlaps in swap mappings, missing swap mappings, page table entries inconsistent with the core map, incore pages which are marked clean but differ from disk-image copies, pages which are locked or intransit, and inconsistencies in the free list.

It would be nice if this program analyzed the system in general, rather than just the paging system in particular.