I386_GET_LDT(2)

NAME

     i386_get_ldt, i386_set_ldt -- manage i386 per-process Local Descriptor
     Table entries

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <machine/segments.h>
     #include <machine/sysarch.h>

     int
     i386_get_ldt(int start_sel, union descriptor *descs, int num_sels);

     int
     i386_set_ldt(int start_sel, union descriptor *descs, int num_sels);

DESCRIPTION

     The i386_get_ldt() system call will return the list of i386 descriptors
     that the process has in its LDT.  The i386_set_ldt() system call will set
     a list of i386 descriptors for the current process in its LDT.  Both rou-
     tines accept a starting selector number start_sel, an array of memory
     that will contain the descriptors to be set or returned descs, and the
     number of entries to set or return num_sels.

     The argument descs can be either segment_descriptor or gate_descriptor
     and are defined in <i386/segments.h>.  These structures are defined by
     the architecture as disjoint bit-fields, so care must be taken in con-
     structing them.

     If start_sel is LDT_AUTO_ALLOC, num_sels is 1 and the descriptor pointed
     to by descs is legal, then i386_set_ldt() will allocate a descriptor and
     return its selector number.

     If num_descs is 1, start_sels is valid, and descs is NULL, then
     i386_set_ldt() will free that descriptor (making it available to be real-
     located again later).

     If num_descs is 0, start_sels is 0 and descs is NULL then, as a special
     case, i386_set_ldt() will free all descriptors.

RETURN VALUES

     Upon successful completion, i386_get_ldt() returns the number of descrip-
     tors currently in the LDT.  The i386_set_ldt() system call returns the
     first selector set.  In the case when a descriptor is allocated by the
     kernel, its number will be returned.  Otherwise, a value of -1 is
     returned and the global variable errno is set to indicate the error.

ERRORS

     The i386_get_ldt() and i386_set_ldt() system calls will fail if:

     [EINVAL]		An inappropriate value was used for start_sel or
			num_sels.

     [EACCES]		The caller attempted to use a descriptor that would
			circumvent protection or cause a failure.

SEE ALSO

     i386 Microprocessor Programmer's Reference Manual, Intel

WARNING

     You can really hose your process using this.