I386_GET_LDT(2) System Calls Manual (i386) I386_GET_LDT(2)
i386_get_ldt, i386_set_ldt -- manage i386 per-process Local Descriptor
i386 Architecture Library (libi386, -li386)
i386_get_ldt(int start_sel, union descriptor *descs, int num_sels);
i386_set_ldt(int start_sel, union descriptor *descs, int num_sels);
i386_get_ldt() will return the list of i386 descriptors that the process
has in its LDT. i386_set_ldt() will set a list of i386 descriptors for
the current process in its LDT. Both routines 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
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
Upon successful completion, i386_get_ldt() returns the number of
descriptors currently in the LDT. i386_set_ldt() returns the first
selector set. Otherwise, a value of -1 is returned and the global
variable errno is set to indicate the error.
i386_get_ldt() and i386_set_ldt() will fail if:
[EINVAL] An inappropriate parameter was used for start_sel or num_sels.
[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.
NetBSD 6.1.5 September 20, 1993 NetBSD 6.1.5