NetBSD/share/man/man5/core.5

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.\"     @(#)core.5	8.3 (Berkeley) 12/11/93
.\"
.Dd October 7, 2000
.Dt CORE 5
.Os
.Sh NAME
.Nm core
.Nd memory image file format
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Sh DESCRIPTION
A small number of signals which cause abnormal termination of a process
also cause a record of the process's in-core state to be written
to disk for later examination by one of the available debuggers
(see
.Xr signal 7 ) .
.Pp
This memory image is written to a file named from a per-process template;
provided the terminated process had write permission, and provided the
abnormality did not cause a system crash.
(In this event, the decision to save the core file is arbitrary, see
.Xr savecore 8 . )
The file is named from a per-process template, mapped to the sysctl
variable
.Em proc.<pid>.corename
(where <pid> has to be replaced by the pid in decimal format of the
process).
This template is either an absolute or relative path name, in which format
characters can be used, preceded by the percent character
.Pq Dq \&% .
The following characters are recognised as format and substituted:
.Bl -tag -width 4n -offset indent -compact
.It Sy n
The process's name
.It Sy p
The PID of the process (in decimal)
.It Sy t
The process's creation date (a la
.Xr time 3 ,
in decimal)
.It Sy u
The login name, as returned by
.Xr getlogin 2
.El
.Pp
By default, the per-process template string points to the default core name
template, which is mapped to the sysctl variable
.Em kern.defcorename .
Changing this value on a live system will change the core name template for
all processes which didn't have a per-process template set.
The default value of the default core name template is
.Nm %n.core
and can be changed at compile-time with the kernel configuration option
.Cd options DEFCORENAME
(see
.Xr options 4 )
.Pp
The per-process template string is inherited on process creation, but is reset
to point to the default core name template on execution of a set-id binary.
.Pp
The maximum size of a core file is limited by
.Xr setrlimit 2 .
Files which would be larger than the limit are not created.
.Pp
The core file contains of a core header followed by a number of
segments. Each segment is preceded by a core segment header.
Both the core header and core segment header are defined in
.Aq Pa sys/core.h .

The core header,
.Fa struct core ,
specifies the lengths of the core header itself and
each of the following core segment headers to allow for any machine
dependent alignment requirements.
.Bd -literal
struct core {
    u_int32_t c_midmag;         /* magic, id, flags */
    u_int16_t c_hdrsize;        /* Size of this header (machdep algn) */
    u_int16_t c_seghdrsize;     /* Size of a segment header */
    u_int32_t c_nseg;           /* # of core segments */
    char      c_name[MAXCOMLEN+1];	/* Copy of p->p_comm */
    u_int32_t c_signo;          /* Killing signal */
    u_long    c_ucode;          /* Signal code */
    u_long    c_cpusize;        /* Size of machine dependent segment */
    u_long    c_tsize;          /* Size of traditional text segment */
    u_long    c_dsize;          /* Size of traditional data segment */
    u_long    c_ssize;          /* Size of traditional stack segment */
};
.Ed
.Pp
The fields of
.Fa struct core
are as follows:
.Bl -tag -width XXXc_seghdrsize
.It c_midmag
Core file machine ID, magic value, and flags.
These values may be extracted with the
.Fn CORE_GETMID ,
.Fn CORE_GETMAGIC ,
and
.Fn CORE_GETFLAG
macros. The machine ID values are listed in
.Aq Pa sys/exec_aout.h .
For a valid core file, the magic value in the header must be
.Dv COREMAGIC .
No flags are defined for the core header.
.It c_hdrsize
Size of this data structure.
.It c_seghdrsize
Size of a segment header.
.It c_nseg
Number of segments that follow this header.
.It c_name
Process name, copied from the p_comm field of
.Fa struct proc .
.It c_signo
Signal that caused the process to dump core.
.It c_ucode
Code associated with the signal.
.It c_cpusize
Size of the segment containing CPU-specific information.
This segment will have the
.Dv CORE_CPU
flag set.
.It c_tsize
Size of the segment containing the program text.
.It c_dsize
Size of the segment containing the program's traditional data area.
.It c_ssize
Size of the segment containing the program's traditional stack area.
This segment will have the
.Dv CORE_STACK
flag set.
.El
The header is followed by
.Fa c_nseg
segments, each of which is preceded with a segment header,
.Fa struct coreseg :
.Bd -literal
struct coreseg {
   u_int32_t c_midmag;  /* magic, id, flags */
   u_long    c_addr;    /* Virtual address of segment */
   u_long    c_size;    /* Size of this segment */
};
.Ed
.Pp
The fields of
.Fa struct coreseg
are as follows:
.Bl -tag -width XXXc_midmag
.It c_midmag
Core segment magic value and flags.
These values may be extracted with the
.Fn CORE_GETMAGIC
and
.Fn CORE_GETFLAG
macros.
The magic value in the segment header must be
.Dv CORESEGMAGIC .
Exactly one of of the flags
.Dv CORE_CPU ,
.Dv CORE_DATA ,
or
.Dv CORE_STACK
will be set to indicate the segment type.
.It c_addr
Virtual address of the segment in the program image.
Meaningless if the segment type is
.Dv CORE_CPU .
.It c_size
Size of the segment, not including this header.
.El
.Sh SEE ALSO
.Xr gdb 1 ,
.Xr setrlimit 2 ,
.Xr sysctl 3 ,
.Xr signal 7 ,
.Xr sysctl 8
.Sh HISTORY
A
.Nm core
file format appeared in
.At v6 .
.Sh BUGS
There is no standard location or name for the
CPU-dependent data structure stored in the
.Dv CORE_CPU
segment.