Obtaining Kernel Data Structure Information

The Oracle Solaris kernel provides data type information in structures that can be inspected with either kmdb or mdb.

The kmdb and mdb dcmds can be used only with objects that contain compressed symbolic debugging information that has been designed for use with mdb. This information is currently available only for certain Oracle Solaris kernel modules. The SUNWzlib package must be installed to process the symbolic debugging information.

The following example demonstrates how to display the data in the scsi_pkt structure.

Example 22–15 Displaying Kernel Data Structures With a Debugger

> 7079ceb0::print -t 'struct scsi_pkt'
{
    opaque_t pkt_ha_private = 0x7079ce20
    struct scsi_address pkt_address = {
        struct scsi_hba_tran *a_hba_tran = 0x70175e68
        ushort_t a_target = 0x6
        uchar_t a_lun = 0
        uchar_t a_sublun = 0
    }
    opaque_t pkt_private = 0x708db4d0
    int (*)() *pkt_comp = sd_intr
    uint_t pkt_flags = 0
    int pkt_time = 0x78
    uchar_t *pkt_scbp = 0x7079ce74
    uchar_t *pkt_cdbp = 0x7079ce64
    ssize_t pkt_resid = 0
    uint_t pkt_state = 0x37
    uint_t pkt_statistics = 0
    uchar_t pkt_reason = 0
}

The size of a data structure can be useful in debugging. Use the ::sizeof dcmd to obtain the size of a structure, as shown in the following example.

Example 22–16 Displaying the Size of a Kernel Data Structure

> ::sizeof struct scsi_pkt
sizeof (struct scsi_pkt) = 0x58

The address of a specific member within a structure is also useful in debugging. Several methods are available for determining a member's address.

Use the ::offsetof dcmd to obtain the offset for a given member of a structure, as in the following example.

Example 22–17 Displaying the Offset to a Kernel Data Structure

> ::offsetof struct scsi_pkt pkt_state
offsetof (struct pkt_state) = 0x48

Use the ::print dcmd with the -a option to display the addresses of all members of a structure, as in the following example.

Example 22–18 Displaying the Relative Addresses of a Kernel Data Structure

> ::print -a struct scsi_pkt
{
    0 pkt_ha_private
    8 pkt_address {
    ...
    }
    18 pkt_private
    ...
}

If an address is specified with ::print in conjunction with the -a option, the absolute address for each member is displayed.

Example 22–19 Displaying the Absolute Addresses of a Kernel Data Structure

> 10000000::print -a struct scsi_pkt
{
    10000000 pkt_ha_private
    10000008 pkt_address {
    ...
    }
    10000018 pkt_private
    ...
}

The ::print, ::sizeof and ::offsetof dcmds enable you to debug problems when your driver interacts with the Oracle Solaris kernel.

This facility provides access to raw kernel data structures. You can examine any structure whether or not that structure appears as part of the DDI. Therefore, you should refrain from relying on any data structure that is not explicitly part of the DDI.

These dcmds should be used only with objects that contain compressed symbolic debugging information that has been designed for use with mdb. Symbolic debugging information is currently available for certain Oracle Solaris kernel modules only. The SUNWzlib (32-bit) or SUNWzlibx (64-bit) decompression software must be installed to process the symbolic debugging information. The kmdb debugger can process symbolic type data with or without the SUNWzlib or SUNWzlibx packages.