| I386_GET_LDT(2) | 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
<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);
The
i386_get_ldt()
system call returns a list of the i386 descriptors in the current process'
LDT. The i386_set_ldt() system call 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 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 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 reallocated 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 descriptors currently in the LDT. The
i386_set_ldt() system call returns the first
selector set on success. 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.
The i386_get_ldt() and
i386_set_ldt() system calls will fail if:
i386 Microprocessor Programmer's Reference Manual, Intel
You can really hose your process using this.
| October 14, 2006 | Debian |