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I386_GET_LDT(2) System Calls Manual (i386) I386_GET_LDT(2)

NAME

i386_get_ldt, i386_set_ldtmanage i386 per-process Local Descriptor Table entries

SYNOPSIS

#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);

DESCRIPTION

i386_get_ldt() returns a list of the i386 descriptors in the current process' LDT. i386_set_ldt() sets a list of i386 descriptors in the current process' LDT. For both routines, start_sel specifies the index of the selector in the LDT at which to begin and descs points to an array of num_sels descriptors to be set or returned.
Each entry in the descs array can be either a segment_descriptor or a gate_descriptor, as defined in <i386/segments.h>. These structures are defined by the architecture 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.

RETURN VALUES

Upon successful completion, i386_get_ldt() returns the number of i386 descriptors copied into descs from the current process' LDT. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.
Upon successful completion, i386_set_ldt() returns the first selector set; if the kernel allocated a descriptor in the LDT, the allocated index is returned. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.

ERRORS

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.

REFERENCES

Intel, i386 Microprocessor Programmer's Reference Manual.

WARNING

You can really hose your process using this.
September 10, 2015 OpenBSD-5.9