1 /* 2 * ldt.h 3 * 4 * Definitions of structures used with the modify_ldt system call. 5 */ 6 #ifndef _ASM_X86_LDT_H 7 #define _ASM_X86_LDT_H 8 9 /* Maximum number of LDT entries supported. */ 10 #define LDT_ENTRIES 8192 11 /* The size of each LDT entry. */ 12 #define LDT_ENTRY_SIZE 8 13 14 #ifndef __ASSEMBLY__ 15 /* 16 * Note on 64bit base and limit is ignored and you cannot set DS/ES/CS 17 * not to the default values if you still want to do syscalls. This 18 * call is more for 32bit mode therefore. 19 */ 20 struct user_desc { 21 unsigned int entry_number; 22 unsigned int base_addr; 23 unsigned int limit; 24 unsigned int seg_32bit:1; 25 unsigned int contents:2; 26 unsigned int read_exec_only:1; 27 unsigned int limit_in_pages:1; 28 unsigned int seg_not_present:1; 29 unsigned int useable:1; 30 #ifdef __x86_64__ 31 /* 32 * Because this bit is not present in 32-bit user code, user 33 * programs can pass uninitialized values here. Therefore, in 34 * any context in which a user_desc comes from a 32-bit program, 35 * the kernel must act as though lm == 0, regardless of the 36 * actual value. 37 */ 38 unsigned int lm:1; 39 #endif 40 }; 41 42 #define MODIFY_LDT_CONTENTS_DATA 0 43 #define MODIFY_LDT_CONTENTS_STACK 1 44 #define MODIFY_LDT_CONTENTS_CODE 2 45 46 #endif /* !__ASSEMBLY__ */ 47 #endif /* _ASM_X86_LDT_H */ 48