NAME

       ksyms — kernel symbol table interface

SYNOPSIS

       device ksyms

DESCRIPTION

       The  /dev/ksyms character device provides a read-only interface to a snapshot of the kernel symbol table.
       The in-kernel symbol manager is designed to be able to handle many types of symbols tables, however, only
       elf(5) symbol tables are supported by this device.  The ELF format image contains two sections: a  symbol
       table and a corresponding string table.

             Symbol Table
                     The SYMTAB section contains the symbol table entries present in the current running kernel,
                     including  the  symbol table entries of any loaded modules.  The symbols are ordered by the
                     kernel module load time starting with kernel file symbols  first,  followed  by  the  first
                     loaded module's symbols and so on.

             String Table
                     The  STRTAB section contains the symbol name strings from the kernel and any loaded modules
                     that the symbol table entries reference.

       Elf formatted symbol table data read from the /dev/ksyms file represents the state of the kernel  at  the
       time when the device is opened.  Since /dev/ksyms has no text or data, most of the fields are initialized
       to  NULL.   The ksyms driver does not block the loading or unloading of modules into the kernel while the
       /dev/ksyms file is open but may contain stale data.

IOCTLS

       The ioctl(2) command codes below are defined in ⟨sys/ksyms.h⟩.

       The (third) argument to the ioctl(2) should be a pointer to the type indicated.

             KIOCGSIZE (size_t)
                     Returns the total size of the current symbol table.  This can be  used  when  allocating  a
                     buffer to make a copy of the kernel symbol table.

             KIOCGADDR (void *)
                     Returns the address of the kernel symbol table mapped in the process memory.

FILES

       /dev/ksyms

ERRORS

       An open(2) of /dev/ksyms will fail if:

       [EBUSY]            The  device  is already open.  A process must close /dev/ksyms before it can be opened
                          again.

       [ENOMEM]           There is a resource shortage in the kernel.

       [ENXIO]            The driver was unsuccessful in creating a snapshot of the kernel symbol  table.   This
                          may occur if the kernel was in the process of loading or unloading a module.

SEE ALSO

       ioctl(2), nlist(3), elf(5), kldload(8)

HISTORY

       A ksyms device exists in many different operating systems.  This implementation is similar in function to
       the Solaris and NetBSD ksyms driver.

       The ksyms driver first appeared in FreeBSD 8.0 to support lockstat(1).

AUTHORS

       The ksyms driver was written by Stacey Son <sson@FreeBSD.org>.

BUGS

       Because  files  can  be  dynamically  linked into the kernel at any time the symbol information can vary.
       When you open the /dev/ksyms file, you have access to an ELF image which represents  a  snapshot  of  the
       state  of  the kernel symbol information at that instant in time.  Keeping the device open does not block
       the loading or unloading of kernel modules.  To get a new snapshot you must close and re-open the device.

       A process is only allowed to open the /dev/ksyms file once  at  a  time.   The  process  must  close  the
       /dev/ksyms before it is allowed to open it again.

       The  ksyms  driver uses the calling process' memory address space to store the snapshot.  ioctl(2) can be
       used to get the memory address where the symbol table is stored to save kernel memory.  mmap(2) may  also
       be used but it will map it to another address.

Debian                                            April 5, 2009                                         KSYMS(4)