The info member

Updated: April 19, 2023

The startup_header structure's info member is an array of startup_info* structures that provide a communications area between the IPL and the startup code.

When the IPL code detects system features (e.g., amount of memory installed, current time, information about the bus used on the system, etc.), it stores this information in the info array so that the startup code can retrieve it later. This design saves the startup code from repeating the same detection logic as the IPL. The startup_info* structures and enumerated types include:

startup_info_hdr, startup_info_types, startup_info_skip, startup_info_mem and startup_info_mem_extended, startup_info_disk, startup_info_time, startup_info_box, bootargs_entry, startup_trailer


The info member is declared as an array of _Uint32t fields. This declaration allocates a storage area that contains a set of structures, each beginning with a startup_info_hdr header:

struct startup_info_hdr {
    _Uint16t        type;
    _Uint16t        size;
Member Type Description
type _Uint16t One of the startup_info_types enumerated values (see startup_info_types below)
size _Uint16t Size of the current startup_info_* structure, in bytes


enum startup_info_types {
    STARTUP_INFO_SKIP = 0,	/* If size 0 then end of list */
    STARTUP_INFO_USER = 0x8000	/* User reserved numbers start here */

The startup_info_hdr enumerated types include:

Ignore this field. If the corresponding size member is 0, this is the end of the info list.
A startup_info_mem or startup_info_mem_extended structure is present.
A startup_info_disk structure is present.
A startup_info_time structure is present.
A startup_info_box structure is present.


This structure is used to indicate the end of the info list; it stores no extra information.

struct startup_info_skip {
    struct startup_info_hdr hdr;

startup_info_mem and startup_info_mem_extended

These structures each contain an address and size pair defining a chunk of memory that should be added to procnto's free memory pool.

The startup_info_mem structure is defined as follows:
struct startup_info_mem {
    struct startup_info_hdr hdr;
    _Uint32t                addr;
    _Uint32t                size;
Member Type Description
startup_info_hdr struct Standard info array header structure
addr _Uint32t Memory block start address
size _Uint32t Memory block size, in bytes

The addr and size fields are 32 bits long, so memory is limited to 4 GB. For larger memory blocks, the startup_info_mem_extended structure is used:

struct startup_info_mem_extended {
    struct startup_info_mem mem;
    _Uint32t            addr_hi;
    _Uint32t            size_hi;
Member Type Description
startup_info_mem struct The structure for memory blocks that are less than 4 GB
addr_hi _Uint32t High portion of the memory address (see below)
size_hi _Uint32t High portion of the memory size (see below)

For the extended structure, you can determine the address and size from the addr_hi and size_hi members and the encapsulated startup_info_mem structure as follows:

((paddr64_t) addr_hi << 32) | mem.addr
((paddr64_t) size_hi << 32) | mem.size

More than one startup_info_mem or startup_info_mem_extended structure may be present to accommodate systems that have free memory located in various blocks throughout the address space.

Both structures are identified by a type member of STARTUP_INFO_MEM in the startup_info_hdr structure; use the size field in the header to tell them apart.


The startup_info_disk structure contains information about any hard disks detected. It is defined as follows:

struct startup_info_disk {
    struct startup_info_hdr hdr;
    _Uint8t                 drive;
    _Uint8t                 zero;
    _Uint16t                heads;
    _Uint16t                cylinders;
    _Uint16t                sectors;
    _Uint32t                blocks;
Member Type Description
startup_info_hdr struct Standard info array header structure
drive _Uint8t Drive number
zero _Uint8t Reserved; must be zero
heads _Uint16t Number of heads present
cylinders _Uint16t Number of cylinders present
sectors _Uint16t Number of sectors present
blocks _Uint32t Total block size of device. Assuming 512 bytes per block, the total size is calculated as heads × cylinders × sectors.


The startup_info_time structure contains a record of the system's most recent startup time. It is defined as follows:

struct startup_info_time {
    struct startup_info_hdr hdr;
    _Uint32t                time;
Member Type Description
startup_info_hdr struct Standard info array header structure
time _Uint32t Current time as the number of seconds since 1970 01 01 00:00:00 GMT.


struct startup_info_box {
    struct startup_info_hdr hdr;
    _Uint8t                 boxtype;
    _Uint8t                 bustype;
    _Uint8t                 spare[2];
Member Type Description
startup_info_hdr struct Standard info array header structure
boxtype _Uint8t  
bustype _Uint8t  
spare[2] _Uint8t Reserved, must be zero


struct bootargs_entry {
    _Uint8t     size_lo;    /* Includes entire structure */
    _Uint8t     size_hi;
    _Int8t      argc;
    _Int8t      envc;
    _Uint32t    shdr_addr;
    char        args[1];    /* variable length */
Member Type Description
size_lo _Uint8t  
size_hi _Uint8t  
argc _Int8t  
envc _Int8t  
shdr_addr _Uint32t  
args[1] char  


The startup_trailer structure contains a checksum for the startup_header structure, calculated from the start of the header to the start of the trailer (this structure). It is defined as follows:

struct startup_trailer {
    unsigned long   cksum;
Member Type Description
cksum _Uint32t Checksum from start of header to start of trailer