1MODIFY_LDT(2)              Linux Programmer's Manual             MODIFY_LDT(2)
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NAME

6       modify_ldt - get or set ldt
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SYNOPSIS

9       #include <sys/types.h>
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11       int modify_ldt(int func, void *ptr, unsigned long bytecount);
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DESCRIPTION

14       modify_ldt()  reads  or  writes  the local descriptor table (ldt) for a
15       process.  The ldt is a per-process memory management table used by  the
16       i386  processor.   For more information on this table, see an Intel 386
17       processor handbook.
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19       When func is 0, modify_ldt() reads the ldt into the memory  pointed  to
20       by  ptr.   The number of bytes read is the smaller of bytecount and the
21       actual size of the ldt.
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23       When func is 1, modify_ldt() modifies one ldt entry.  ptr points  to  a
24       user_desc  structure  and  bytecount must equal the size of this struc‐
25       ture.
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27       The user_desc structure is defined in <asm/ldt.h> as:
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29           struct user_desc {
30               unsigned int  entry_number;
31               unsigned long base_addr;
32               unsigned int  limit;
33               unsigned int  seg_32bit:1;
34               unsigned int  contents:2;
35               unsigned int  read_exec_only:1;
36               unsigned int  limit_in_pages:1;
37               unsigned int  seg_not_present:1;
38               unsigned int  useable:1;
39           };
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41       In Linux 2.4 and earlier, this structure was named modify_ldt_ldt_s.
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RETURN VALUE

44       On success, modify_ldt() returns either the actual number of bytes read
45       (for  reading) or 0 (for writing).  On failure, modify_ldt() returns -1
46       and sets errno to indicate the error.
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ERRORS

49       EFAULT ptr points outside the address space.
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51       EINVAL ptr is 0, or func is 1 and bytecount is not equal to the size of
52              the  structure  modify_ldt_ldt_s,  or  func is 1 and the new ldt
53              entry has invalid values.
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55       ENOSYS func is neither 0 nor 1.
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CONFORMING TO

58       This call is Linux-specific and should not be used in programs intended
59       to be portable.
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NOTES

62       Glibc  does  not  provide a wrapper for this system call; call it using
63       syscall(2).
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SEE ALSO

66       vm86(2)
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COLOPHON

69       This page is part of release 3.25 of the Linux  man-pages  project.   A
70       description  of  the project, and information about reporting bugs, can
71       be found at http://www.kernel.org/doc/man-pages/.
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75Linux                             2007-06-01                     MODIFY_LDT(2)
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