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By adding support for longer NOPs there are a few more alternatives that can turn into a single instruction. Add up to NOP11, the same limit where GNU as .nops also stops generating longer nops. This is because a number of uarchs have severe decode penalties for more than 3 prefixes. [ bp: Sync up with the version in tools/ while at it. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/r/20230515093020.661756940@infradead.org
90 lines
2.2 KiB
C
90 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_NOPS_H
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#define _ASM_X86_NOPS_H
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#include <asm/asm.h>
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/*
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* Define nops for use with alternative() and for tracing.
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*/
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#ifndef CONFIG_64BIT
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/*
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* Generic 32bit nops from GAS:
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*
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* 1: nop
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* 2: movl %esi,%esi
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* 3: leal 0x0(%esi),%esi
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* 4: leal 0x0(%esi,%eiz,1),%esi
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* 5: leal %ds:0x0(%esi,%eiz,1),%esi
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* 6: leal 0x0(%esi),%esi
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* 7: leal 0x0(%esi,%eiz,1),%esi
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* 8: leal %ds:0x0(%esi,%eiz,1),%esi
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*
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* Except 5 and 8, which are DS prefixed 4 and 7 resp, where GAS would emit 2
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* nop instructions.
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*/
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#define BYTES_NOP1 0x90
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#define BYTES_NOP2 0x89,0xf6
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#define BYTES_NOP3 0x8d,0x76,0x00
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#define BYTES_NOP4 0x8d,0x74,0x26,0x00
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#define BYTES_NOP5 0x3e,BYTES_NOP4
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#define BYTES_NOP6 0x8d,0xb6,0x00,0x00,0x00,0x00
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#define BYTES_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00
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#define BYTES_NOP8 0x3e,BYTES_NOP7
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#define ASM_NOP_MAX 8
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#else
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/*
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* Generic 64bit nops from GAS:
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*
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* 1: nop
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* 2: osp nop
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* 3: nopl (%eax)
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* 4: nopl 0x00(%eax)
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* 5: nopl 0x00(%eax,%eax,1)
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* 6: osp nopl 0x00(%eax,%eax,1)
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* 7: nopl 0x00000000(%eax)
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* 8: nopl 0x00000000(%eax,%eax,1)
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* 9: cs nopl 0x00000000(%eax,%eax,1)
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* 10: osp cs nopl 0x00000000(%eax,%eax,1)
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* 11: osp osp cs nopl 0x00000000(%eax,%eax,1)
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*/
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#define BYTES_NOP1 0x90
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#define BYTES_NOP2 0x66,BYTES_NOP1
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#define BYTES_NOP3 0x0f,0x1f,0x00
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#define BYTES_NOP4 0x0f,0x1f,0x40,0x00
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#define BYTES_NOP5 0x0f,0x1f,0x44,0x00,0x00
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#define BYTES_NOP6 0x66,BYTES_NOP5
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#define BYTES_NOP7 0x0f,0x1f,0x80,0x00,0x00,0x00,0x00
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#define BYTES_NOP8 0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00
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#define BYTES_NOP9 0x2e,BYTES_NOP8
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#define BYTES_NOP10 0x66,BYTES_NOP9
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#define BYTES_NOP11 0x66,BYTES_NOP10
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#define ASM_NOP9 _ASM_BYTES(BYTES_NOP9)
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#define ASM_NOP10 _ASM_BYTES(BYTES_NOP10)
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#define ASM_NOP11 _ASM_BYTES(BYTES_NOP11)
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#define ASM_NOP_MAX 11
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#endif /* CONFIG_64BIT */
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#define ASM_NOP1 _ASM_BYTES(BYTES_NOP1)
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#define ASM_NOP2 _ASM_BYTES(BYTES_NOP2)
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#define ASM_NOP3 _ASM_BYTES(BYTES_NOP3)
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#define ASM_NOP4 _ASM_BYTES(BYTES_NOP4)
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#define ASM_NOP5 _ASM_BYTES(BYTES_NOP5)
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#define ASM_NOP6 _ASM_BYTES(BYTES_NOP6)
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#define ASM_NOP7 _ASM_BYTES(BYTES_NOP7)
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#define ASM_NOP8 _ASM_BYTES(BYTES_NOP8)
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#ifndef __ASSEMBLY__
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extern const unsigned char * const x86_nops[];
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#endif
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#endif /* _ASM_X86_NOPS_H */
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