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RedHat 9 (Linux i386) - man page for modify_ldt (redhat section 2)

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

modify_ldt - get or set ldt
#include <linux/ldt.h> #include <linux/unistd.h> _syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long, bytecount ) int modify_ldt(int func, void *ptr, unsigned long bytecount);
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 modify_ldt_ldt_s structure and bytecount must equal the size of this structure.
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.
ENOSYS func is neither 0 nor 1. 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. EFAULT ptr points outside the address space.
This call in Linux-specific and should not be used in programs intended to be portable.
vm86(2) Linux 1.3.6 1995-07-22 MODIFY_LDT(2)