I386_GET_LDT(2) BSD Programmer's Manual (i386) I386_GET_LDT(2)
i386_get_ldt, i386_set_ldt - manage i386 per-process Local Descriptor Table entries
#include <sys/types.h> #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);
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 num_sels. The argument descs can be either segment_descriptor or gate_descriptor, as defined in <i386/segments.h>. These structures are defined by the ar- chitecture as disjoint bit-fields, so care must be taken in constructing them. Before this API can be used the functionality has to be enabled using the machdep.userldt sysctl(8) variable. Note: Code using the i386_get_ldt() and i386_set_ldt() functions must be compiled using -li386.
Upon successful completion, i386_get_ldt() returns the number of descrip- tors 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.
Intel, i386 Microprocessor Programmer's Reference Manual.
You can really hose your process using this. MirOS BSD #10-current September 20, 1993 1
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