V1/man/man5/core.5

        11/3/71                                                      CORE (v)


NAME              format of core image

SYNOPSIS

DESCRIPTION       Three conditions cause UNIX to write out the core image of
                  an executing program: the program generates an unexpected
                  trap (by a bus error or illegal instruction); the user
                  sends a quit signal (which has not been turned off by the
                  program); a trap is simulated by the floating point
                  simulator. The core image is called "core" and is written
                  in the current working directory (provided it can be;
                  normal access controls apply). It is exactly 8192+64 bytes
                  long. The first 8192 represent the actual contents of
                  memory at the time of the fault; the last 64 are the
                  contents of the system's per--user data area for this
                  process. Only the first word of this area will be
                  described.

                  When any trap which is not an I/O interrupt occurs, all the
                  useful registers are stored on the stack. After all the
                  registers have been stored, the contents of are placed in
                  the first cell of the user area; this cell is called u.sp.
                  Therefore, within the core image proper, there is an area
                  which contains the following registers in the following
                  order (increasing addresses):

                                (u.sp)-->sc
                           mq
                           ac
                           r5
                           r4
                           r3
                           r2
                           ri
                           r0
                           pc (at time of fault)
                           processor status (at time of fault)

                  The last two are stored by the hardware. It follows that
                  the contents of at the time of the fault were (u.sp) plus
                  22(10).

                  The t--bit (trap bit) in the stored status will be on when a
                  quit caused the generation of the core image, since this
                  bit is used in the implementation of quits.

FILES

SEE ALSO

DIAGNOSTICS
        11/3/71              CORE (v)


BUGS

OWNER             ken, dmr