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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

include/asm-x86/nops.h

+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"