Contains an image of a 32-bit or 64-bit process at the time of an error.
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 contents of a core dump are organized sequentially in the core file as follows:
| Item | Description |
|---|---|
| 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. |
| thrdctx structures | Defines kernel thread state information. Since the faulting thread thrdctx structure is directly saved in the core header, additional structures are saved here only for multi-threaded programs. |
| segregion structures | Contains the address, size, and type for shared memory segments of the faulting process. |
| 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. |
| vm_infox structures | (Optional) Contains offset and size information for memory mapped regions. |
| Memory mapped regions | (Optional) Contains the memory mapped regions. |
The core_dumpx structure, defined by the core.h file, occurs at the beginning of a core file. The core_dumpx structure includes the following fields:
| Item | 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:
|
| 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 |
The c_flt field in the core dump contains the thrdctx structure of the faulting thread. The thrdctx structure includes the thread data and registers as they existed at the time of the fault. The format of the thread context structure is defined by thrdctx structure (in the core.h header file) as follows:
| Item | Description | |
|---|---|---|
| thrdctx | thrdsinfo64 __context64 mstsave | thread data (in procinfo.h header file) state of registers if 64-bit process, or state of registers if 32-bit process |
The c_u field follows this information in the core dump. The c_u field contains the userx structure including the user structure fields, and the process data as they existed at the time of the fault. The format of the process information structure is defined by the userx structure (in the core.h header file) as follows:
| Item | Description | |
|---|---|---|
| userx | procsinfo64 | process data (in procinfo.h header file) |
The ld_info structure and then the thrdctx structures of the other threads (if the process is multi-threaded) follow in the core dump.
The segregion structure and then the user-mode stack follow in the core dump.
The segregion structure contains the information about a shared memory region of the faulting process.
| Item | Description | |
|---|---|---|
| segregion | addr size segflags | segment start address size of the segment type of the document |
The first three fields of the core_dumpx header in AIX 4.3 are the same as that of the core_dump header in AIX 4.2. However, the c_entries are always zero on AIX 4.3 systems to distinguish them from the AIX 4.2 core file formats. Further, the pi_flags2 field of the procsinfo64 structure determines if the core file is of a 32-bit process or a 64-bit process.
The AIX 4.3 operating system can be forced to create core files in a AIX 4.2 core file format via the SMIT tool. However, this enforcement is valid only for 32-bit processes.
By default, the user data, anonymously mapped regions, and vm_infox structures are not included in a core dump. This partial core dump includes the current thread stack, the thread thrdctx 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 or setrlimit64 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 user data section, vm_infox, and anonymously mapped region structures are included in the core dump.