NAME
modify_ldt - get or set ldt
SYNOPSIS
#include <sys/types.h>
I int modify_ldt(int func , void * ptr , unsigned long bytecount );
DESCRIPTION
R 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,
R modify_ldt ()
reads the ldt into the memory pointed to by
R ptr .
The number of bytes read is the smaller of
bytecount
and the actual size of the ldt.
When
func
is 1,
R 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
R modify_ldt_ldt_s .
RETURN VALUE
On success,
R modify_ldt ()
returns either the actual number of bytes read (for reading)
or 0 (for writing).
On failure,
R modify_ldt ()
returns -1 and sets
R errno
to indicate the error.
ERRORS
EFAULT
ptr
points outside the address space.
EINVAL
ptr
is 0,
or
func
is 1 and
bytecount
is not equal to the size of the structure
R modify_ldt_ldt_s ,
or
func
is 1 and the new ldt entry has invalid values.
ENOSYS
func
is neither 0 nor 1.
CONFORMING TO
This call is Linux specific and should not be used in programs intended
to be portable.
NOTES
Glibc does not provide a wrapper for this system call; call it using
syscall(2).
SEE ALSO
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