modify_ldt — get or set ldt
#include <sys/types.h>
int
modify_ldt( |
int | func, |
void * | ptr, | |
unsigned long | bytecount) ; |
modify_ldt
() reads or writes
the local descriptor table (ldt) for a process. The ldt is a
per-process memory management table used by the i386
processor. For more information on this table, see an Intel
386 processor handbook.
When func
is 0,
modify_ldt
() reads the ldt into
the memory pointed to by ptr
. The number of bytes read
is the smaller of bytecount
and the actual size
of the ldt.
When func
is 1,
modify_ldt
() modifies one ldt
entry. ptr
points to
a user_desc
structure and bytecount
must equal the size
of this structure.
The user_desc
structure is defined in <asm/ldt.h> as:
struct user_desc { unsigned int entry_number
;unsigned long base_addr
;unsigned int limit
;unsigned int seg_32bit
:1;unsigned int contents
:2;unsigned int read_exec_only
:1;unsigned int limit_in_pages
:1;unsigned int seg_not_present
:1;unsigned int useable
:1;};
In Linux 2.4 and earlier, this structure was named
modify_ldt_ldt_s
.
On success, modify_ldt
()
returns either the actual number of bytes read (for reading)
or 0 (for writing). On failure, modify_ldt
() returns −1 and sets
errno
to indicate the error.
ptr
points
outside the address space.
ptr
is 0, or
func
is 1 and
bytecount
is
not equal to the size of the structure modify_ldt_ldt_s
, or
func
is 1 and
the new ldt entry has invalid values.
func
is
neither 0 nor 1.
This call is Linux specific and should not be used in programs intended to be portable.
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