CORE(5) NetBSD 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 per- cent character (``%''). The following characters are recognized as for- mat 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 pro- vides 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 { 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 */ 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 struc- tures. 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 con- text, 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 con- tents of the execution context. For a complete list of available ptrace(2) request types for a given architecture, refer to that architec- ture'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. Mean- ingless 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 1 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 struc- ture stored in the CORE_CPU segment. NetBSD 10.1 December 6, 2019 NetBSD 10.1
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