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I386_GET_LDT(2)             BSD System Calls Manual            I386_GET_LDT(2)

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

     Standard C Library (libc, -lc)

     #include <architecture/i386/table.h>
     #include <i386/user_ldt.h>

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

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

     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 routines
     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 code_desc_t, data_desc_t or call_gate_t
     and are defined in <architecture/i386/desc.h>.  These structures are
     defined by the architecture as disjoint bit-fields, so care must be taken
     in constructing 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 reallocated
     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.

     Upon successful completion, i386_get_ldt() returns the number of descrip-tors descriptors
     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.

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

     [EINVAL]           An inappropriate value was used for start_sel or

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

     i386 Microprocessor Programmer's Reference Manual, Intel

     You can really hose your process using this.

BSD                           September 20, 1993                           BSD