NAME    [Toc]    [Back]

     amd64_get_ldt, amd64_set_ldt - manage amd64 per-process  Local Descriptor
     Table entries

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <machine/segments.h>
     #include <machine/sysarch.h>

     int
     amd64_get_ldt(int  start_sel,  union  descriptor *descs, int
num_sels);

     int
     amd64_set_ldt(int start_sel, union  descriptor  *descs,  int
num_sels);

DESCRIPTION    [Toc]    [Back]

     amd64_get_ldt()  will  return  the list of amd64 descriptors
that the process
 has in its LDT.  amd64_set_ldt() will  set  a  list  of
amd64 descriptors
  for the current process in its LDT.  Both routines accept a starting
     selector number start_sel, an array of memory that will contain the descriptors
 to be set or returned descs, and the number of entries to set
     or return num_sels.

     The argument  descs  can  be  either  segment_descriptor  or
gate_descriptor,
     as  defined in <amd64/segments.h>.  These structures are defined by the
     architecture as disjoint bit-fields, so care must  be  taken
in constructing
 them.

     Before  this API can be used the functionality has to be enabled using the
     machdep.userldt sysctl(8) variable.

     Note: Code using  the  amd64_get_ldt()  and  amd64_set_ldt()
functions must
     be compiled using -lamd64.

RETURN VALUES    [Toc]    [Back]

     Upon successful completion, amd64_get_ldt() returns the number of descriptors
 currently in the LDT.  amd64_set_ldt() returns the
first selector
 set.  Otherwise, a value of -1 is returned and the global variable
     errno is set to indicate the error.

ERRORS    [Toc]    [Back]

     amd64_get_ldt() and amd64_set_ldt() will fail if:

     [EINVAL]  An inappropriate parameter was used for  start_sel
or num_sels.

     [EACCES]   The  caller  attempted  to  use a descriptor that
would circumvent
               protection or cause a failure.

REFERENCES    [Toc]    [Back]

     Intel, AMD64 Microprocessor Programmer's Reference Manual.

WARNING    [Toc]    [Back]

     You can really hose your process using this.

OpenBSD     3.6                       September     20,      1993