core File Format

AIX Version 4 Files Reference

core File Format

Purpose

Contains an image of a process at the time of an error.

Description

A core file is created in the current directory when various errors occur. Errors such as memory-address violations, illegal instructions, bus errors, and user-generated quit signals commonly cause this core dump. The core file that is created contains a memory image of the terminated process. A process with a saved user ID that differs from the real user ID does not produce a memory image. The same holds true for the group ID (GID) and effective group ID. The contents of a core dump are organized sequentially in the core file as follows:

Core header	Defines basic information about the core dump, and contains offsets that locate the remainder of the core dump information.
ldinfo structures	Defines loader information.
mstsave structures	Defines kernel thread state information. Since the faulting thread mstsave structure is directly saved in the core header, additional structures are saved here only for multi-threaded programs.
Default user stack	Contains a copy of the user stack at the time of the core dump.
Default data area	(Optional) Contains the user data section.
Memory mapped regions	(Optional) Contains the anonymously mapped regions.
vm_info structures	(Optional) Contains offset and size information for memory mapped regions.

By default, the user data is, anonymously mapped regions, and vm_info structures are not included in a core dump. This partial core dump includes the current process stack, thread stack, the thread mstsave structures, the user structure, and the state of the registers at the time of the fault. A partial core dump contains sufficient information for a stack traceback. The size of a core dump can also be limited by the setrlimit subroutine.

To enable a full core dump, set the SA_FULLDUMP flag in the sigaction subroutine for the signal that is to generate a full core dump. If this flag is set when the core is dumped, the data section is, anonymously mapped regions, and vm_info structures are included in the core dump.

The format of the core header is defined by the core_dump structure (in the core.h header file), which is organized as follows:

Field Type	Field Name	Description
char	c_signo	The number of the signal which caused the error
char	c_flag	A bit field which describes the core dump type. The meanings of the bits are as follows:
		FULL_CORE	core contains the data sections (0x01)
		CORE_VERSION_1	core was generated by version 4 or higher of the operating system (0x02)
		MSTS_VALID	core contains mstsave structures (0x04)
		CORE_BIGDATA	core contains big data (0x08)
		UBLOCK_VALID	core contains the u_block structure (0x10)
		USTACK_VALID	core contains the user stack (0x20)
		LE_VALID	core contains at least one module (0x40)
		CORE_TRUNC	core was truncated (0x80)
ushort	c_entries	The number of core dump modules
struct ld_info *	c_tab	The offset to the beginning of the core table
caddr_t	c_stack	The offset to the beginning of the user stack
int	c_size	The size of the user stack
struct mstsave	c_mst	A copy of the faulting mst
struct user	c_u	A copy of the user structure
int	c_nmsts	The number of mstsave structures referenced by the `c_msts` field
struct mstsave *	c_msts	The offset to the other threads' mstsave structures
int	c_datasize	The size of the data region
caddr_t	c_data	The offset to user data
int	c_vmregions	The number of anonymously mapped regions
struct vm_info *	c_vmm	The offset to the start of the vm_info table

Related Information

The param.h file.

The adb command, dbx command.

The raise subroutine, setrlimit subroutine, setuid subroutine, sigaction subroutine.

The Header Files Overview in AIX Version 4.3 Files Reference defines header files, describes how they are used, and lists several header files for which information is provided in this documentation.