CORE(5)

CORE(5) | File Formats Manual | CORE(5)

# NAME

`core` —
memory image file format

# SYNOPSIS

`#include <sys/param.h>`

For a.out-format core files:

`#include <sys/core.h>`

For ELF-format core files:

`#include <sys/exec.h>`
`#include <sys/exec_elf.h>`

# 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 signal(7)).

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 savecore(8).) The file is named from a per-process template, mapped to the sysctl variable 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 (“%”). The following characters are recognized as format and substituted:

n
  The process's name
p
  The PID of the process (in decimal)
t
  The process's creation date (a la time(3), in decimal)
u
  The login name, as returned by getlogin(2)

By default, the per-process template string points to the default core name template, which is mapped to the sysctl variable 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 `%n.core` and can be changed at compile-time with the kernel configuration option `options DEFCORENAME` (see options(4))

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.

The maximum size of a core file is limited by setrlimit(2). Files which would be larger than the limit are not created.

## ELF CORE FORMAT

ELF-format core files are described by a standard ELF exec header and a series of ELF program headers. Each program header describes a range of the virtual address space of the process.

In addition, NetBSD ELF core files include an ELF note section which provides additional information about the process. The first note in the note section has a note name of “NetBSD-CORE” and a note type of `ELF_NOTE_NETBSD_CORE_PROCINFO` (`1`), and contains the following structure:

    struct netbsd_elfcore_procinfo {
       /* Version 1 fields start here. */
        uint32_t cpi_version;      /* netbsd_elfcore_procinfo version */
        uint32_t cpi_cpisize;      /* sizeof(netbsd_elfcore_procinfo) */
        uint32_t cpi_signo;        /* killing signal */
        uint32_t cpi_sigcode;      /* signal code */
        uint32_t cpi_sigpend[4];   /* pending signals */
        uint32_t cpi_sigmask[4];   /* blocked signals */
        uint32_t cpi_sigignore[4]; /* blocked signals */
        uint32_t cpi_sigcatch[4];  /* blocked signals */
        int32_t  cpi_pid;          /* process ID */
        int32_t  cpi_ppid;         /* parent process ID */
        int32_t  cpi_pgrp;         /* process group ID */
        int32_t  cpi_sid;          /* session ID */
        uint32_t cpi_ruid;         /* real user ID */
        uint32_t cpi_euid;         /* effective user ID */
        uint32_t cpi_svuid;        /* saved user ID */
        uint32_t cpi_rgid;         /* real group ID */
        uint32_t cpi_egid;         /* effective group ID */
        uint32_t cpi_svgid;        /* saved group ID */
        uint32_t cpi_nlwps;        /* number of LWPs */
        int8_t   cpi_name[32];     /* copy of p->p_comm */
        /* Add version 2 fields below here. */
        int32_t         cpi_siglwp;     /* LWP target of killing signal */
    };

The fields of struct netbsd_elfcore_procinfo are as follows:

cpi_version
  The version of this structure. The current version is defined by the `NETBSD_ELFCORE_PROCINFO_VERSION` constant.
cpi_cpisize
  The size of this structure.
cpi_signo
  Signal that caused the process to dump core.
cpi_sigcode
  Signal-specific code, if any, corresponding to cpi_signo.
cpi_sigpend
  A mask of signals pending delivery to the process. This may be examined by copying it to a sigset_t.
cpi_sigmask
  The set of signals currently blocked by the process. This may be examined by copying it to a sigset_t.
cpi_sigignore
  The set of signals currently being ignored by the process. This may be examined by copying it to a sigset_t.
cpi_sigcatch
  The set of signals with registers signals handlers for the process. This may be examined by copying it to a sigset_t.
cpi_pid
  Process ID of the process.
cpi_ppid
  Process ID of the parent process.
cpi_pgrp
  Process group ID of the process.
cpi_sid
  Session ID of the process.
cpi_ruid
  Real user ID of the process.
cpi_euid
  Effective user ID of the process.
cpi_svuid
  Saved user ID of the process.
cpi_rgid
  Real group ID of the process.
cpi_egid
  Effective group ID of the process.
cpi_svgid
  Saved group ID of the process.
cpi_nlwps
  Number of kernel-visible execution contexts (LWPs) of the process.
cpi_name
  Process name, copied from the p_comm field of struct proc.
cpi_siglwp
  LWP target of killing signal.

The second note with name “NetBSD-CORE” is a note type of `ELF_NOTE_NETBSD_CORE_AUXV` (`2`), and contains an array of AuxInfo structures.

The note section also contains additional notes for each kernel-visible execution context of the process (LWP). These notes have names of the form “NetBSD-CORE@nn” where “nn” is the LWP ID of the execution context, for example: “NetBSD-CORE@1”. These notes contain register and other per-execution context data in the same format as is used by the ptrace(2) system call. The note types correspond to the ptrace(2) request numbers that return the same data. For example, a note with a note type of PT_GETREGS would contain a struct reg with the register contents of the execution context. For a complete list of available ptrace(2) request types for a given architecture, refer to that architecture's ⟨machine/ptrace.h⟩ header file.

## A.OUT CORE FORMAT

The core file consists 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 `<sys/core.h>`.

The core header, 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.

    struct core {
        uint32_t c_midmag;         /* magic, id, flags */
        uint16_t c_hdrsize;        /* Size of this header (machdep algn) */
        uint16_t c_seghdrsize;     /* Size of a segment header */
        uint32_t c_nseg;           /* # of core segments */
        char      c_name[MAXCOMLEN+1];	/* Copy of p->p_comm */
        uint32_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 */
    };

The fields of struct core are as follows:

c_midmag
  Core file machine ID, magic value, and flags. These values may be extracted with the `CORE_GETMID`(), `CORE_GETMAGIC`(), and `CORE_GETFLAG`() macros. The machine ID values are listed in `<sys/exec_aout.h>`. For a valid core file, the magic value in the header must be `COREMAGIC`. No flags are defined for the core header.
c_hdrsize
  Size of this data structure.
c_seghdrsize
  Size of a segment header.
c_nseg
  Number of segments that follow this header.
c_name
  Process name, copied from the p_comm field of struct proc.
c_signo
  Signal that caused the process to dump core.
c_ucode
  Code associated with the signal.
c_cpusize
  Size of the segment containing CPU-specific information. This segment will have the `CORE_CPU` flag set.
c_tsize
  Size of the segment containing the program text.
c_dsize
  Size of the segment containing the program's traditional data area.
c_ssize
  Size of the segment containing the program's traditional stack area. This segment will have the `CORE_STACK` flag set.

The header is followed by c_nseg segments, each of which is preceded with a segment header, struct coreseg:

    struct coreseg {
       uint32_t c_midmag;  /* magic, id, flags */
       u_long    c_addr;    /* Virtual address of segment */
       u_long    c_size;    /* Size of this segment */
    };

The fields of struct coreseg are as follows:

c_midmag
  Core segment magic value and flags. These values may be extracted with the `CORE_GETMAGIC`() and `CORE_GETFLAG`() macros. The magic value in the segment header must be `CORESEGMAGIC`. Exactly one of the flags `CORE_CPU`, `CORE_DATA`, or `CORE_STACK` will be set to indicate the segment type.
c_addr
  Virtual address of the segment in the program image. Meaningless if the segment type is `CORE_CPU`.
c_size
  Size of the segment, not including this header.

# SEE ALSO

gdb(1), setrlimit(2), sysctl(3), a.out(5), elf(5), signal(7), sysctl(8)

# HISTORY

A `core` file format appeared in Version 6 AT&T UNIX. The NetBSD a.out core file format was introduced in NetBSD 1.0. The NetBSD ELF core file format was introduced in NetBSD 1.6.

In releases previous to NetBSD 1.6, ELF program images produced a.out-format core files.

The `cpi_siglwp` member of the `netbsd_elfcore_procinfo` structure first appeared in NetBSD 2.0. However it retained the procinfo version 1, stored in `cpi_version`.

`ELF_NOTE_NETBSD_CORE_AUXV` was added in NetBSD 8.0.

# BUGS

There is no standard location or name for the CPU-dependent data structure stored in the `CORE_CPU` segment.

March 27, 2017 | NetBSD 9.3