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);

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 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.

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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2007-06-01                                              MODIFY_LDT(2)