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MODIFY_LDT(2) Linux Programmer's Manual MODIFY_LDT(2)
NAME
modify_ldt - get or set ldt
SYNOPSIS
#include <sys/types.h>
int modify_ldt(int func, void *ptr, unsigned long bytecount);
Note: There is no glibc wrapper for this system call; see NOTES.
DESCRIPTION
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 struc-
ture.
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.
RETURN VALUE
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.
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 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
vm86(2)
COLOPHON
This page is part of release 3.69 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
Linux 2012-07-13 MODIFY_LDT(2)
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