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NOP is PAUSE, not a NOP instruction. > > - 0f {0c...0f} is reserved space, > except for 0f 0d /1, which is PREFETCHW, not a NOP. > > - 0f {19,1c...1f} is reserved space, > except for 0f 1f /0, which is NOPL. > > Signed-off-by: Peter Zijlstra (Intel) > --- > tools/objtool/arch/x86/decode.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > --- a/tools/objtool/arch/x86/decode.c > +++ b/tools/objtool/arch/x86/decode.c > @@ -494,7 +494,8 @@ int arch_decode_instruction(struct objto > break; > > case 0x90: > - insn->type = INSN_NOP; > + if (prefix != 0xf3) /* REP NOP := PAUSE */ > + insn->type = INSN_NOP; > break; So this covers NOP1 (0x90) and NOP2 (0x66 0x90), right? > > case 0x9c: > @@ -547,13 +548,14 @@ int arch_decode_instruction(struct objto > > } else if (op2 == 0x0b || op2 == 0xb9) { > > - /* ud2 */ > + /* ud2, ud1 */ > insn->type = INSN_BUG; > > - } else if (op2 == 0x0d || op2 == 0x1f) { > + } else if (op2 == 0x1f) { > > - /* nopl/nopw */ > - insn->type = INSN_NOP; > + /* 0f 1f /0 := NOPL */ > + if (modrm_reg == 0) > + insn->type = INSN_NOP; > > } else if (op2 == 0x1e) { > And this covers all other NOPs (0x0f 0x1f ...), including NOP6 which has a 0x66 preifx (0x66 0xf 0x1f ...) ? From arch/x86/include/asm/nops.h we have: /* * Generic 64bit nops from GAS: * * 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 BYTES_NOP1 0x90 #define BYTES_NOP2 0x66,BYTES_NOP1 #define BYTES_NOP3 0x0f,0x1f,0x00 #define BYTES_NOP4 0x0f,0x1f,0x40,0x00 #define BYTES_NOP5 0x0f,0x1f,0x44,0x00,0x00 #define BYTES_NOP6 0x66,BYTES_NOP5 #define BYTES_NOP7 0x0f,0x1f,0x80,0x00,0x00,0x00,0x00 #define BYTES_NOP8 0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00 alex.