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Commit 4cd20952 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Ingo Molnar
Browse files

x86: add comments for NOPs



Add comments describing the various NOP sequences.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 959b3be6
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+45 −17
Original line number Diff line number Diff line
@@ -3,7 +3,14 @@

/* Define nops for use with alternative() */

/* generic versions from gas */
/* generic versions from gas
   1: nop
   2: movl %esi,%esi
   3: leal 0x00(%esi),%esi
   4: leal 0x00(,%esi,1),%esi
   6: leal 0x00000000(%esi),%esi
   7: leal 0x00000000(,%esi,1),%esi
*/
#define GENERIC_NOP1 ".byte 0x90\n"
#define GENERIC_NOP2 ".byte 0x89,0xf6\n"
#define GENERIC_NOP3 ".byte 0x8d,0x76,0x00\n"
@@ -13,7 +20,12 @@
#define GENERIC_NOP7 ".byte 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00\n"
#define GENERIC_NOP8 GENERIC_NOP1 GENERIC_NOP7

/* Opteron 64bit nops */
/* Opteron 64bit nops
   1: nop
   2: osp nop
   3: osp osp nop
   4: osp osp osp nop
*/
#define K8_NOP1 GENERIC_NOP1
#define K8_NOP2	".byte 0x66,0x90\n"
#define K8_NOP3	".byte 0x66,0x66,0x90\n"
@@ -23,8 +35,15 @@
#define K8_NOP7	K8_NOP4 K8_NOP3
#define K8_NOP8	K8_NOP4 K8_NOP4

/* K7 nops */
/* uses eax dependencies (arbitary choice) */
/* K7 nops
   uses eax dependencies (arbitary choice)
   1: nop
   2: movl %eax,%eax
   3: leal (,%eax,1),%eax
   4: leal 0x00(,%eax,1),%eax
   6: leal 0x00000000(%eax),%eax
   7: leal 0x00000000(,%eax,1),%eax
*/
#define K7_NOP1	GENERIC_NOP1
#define K7_NOP2	".byte 0x8b,0xc0\n"
#define K7_NOP3	".byte 0x8d,0x04,0x20\n"
@@ -34,8 +53,17 @@
#define K7_NOP7	".byte 0x8D,0x04,0x05,0,0,0,0\n"
#define K7_NOP8	K7_NOP7 ASM_NOP1

/* P6 nops */
/* uses eax dependencies (Intel-recommended choice) */
/* P6 nops
   uses eax dependencies (Intel-recommended choice)
   1: nop
   2: osp nop
   3: nopl (%eax)
   4: nopl 0x00(%eax)
   5: nopl 0x00(%eax,%eax,1)
   6: osp nopl 0x00(%eax,%eax,1)
   7: nopl 0x00000000(%eax)
   8: nopl 0x00000000(%eax,%eax,1)
*/
#define P6_NOP1	GENERIC_NOP1
#define P6_NOP2	".byte 0x66,0x90\n"
#define P6_NOP3	".byte 0x0f,0x1f,0x00\n"