On Fri, Mar 12, 2021 at 12:32:54PM +0100, Peter Zijlstra wrote: > +#ifndef CONFIG_64BIT > + > +/* > + * Generic 32bit nops from GAS: > + * > + * 1: nop > + * 2: movl %esi,%esi > + * 3: leal 0x0(%esi),%esi > + * 4: leal 0x0(%esi,%eiz,1),%esi > + * 5: leal %ds:0x0(%esi,%eiz,1),%esi > + * 6: leal 0x0(%esi),%esi > + * 7: leal 0x0(%esi,%eiz,1),%esi > + * 8: leal %ds:0x0(%esi,%eiz,1),%esi > * > + * Except 5 and 8, which are DS prefixed 4 and 7 resp, where GAS would emit 2 > + * nop instructions. > */ > +#define BYTES_NOP1 0x90 > +#define BYTES_NOP2 0x89,0xf6 > +#define BYTES_NOP3 0x8d,0x76,0x00 > +#define BYTES_NOP4 0x8d,0x74,0x26,0x00 > +#define BYTES_NOP5 0x3e,BYTES_NOP4 > +#define BYTES_NOP6 0x8d,0xb6,0x00,0x00,0x00,0x00 > +#define BYTES_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00 > +#define BYTES_NOP8 0x3e,BYTES_NOP7 > + > +#else > > +/* > + * 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 > > +#endif /* CONFIG_64BIT */
Note that this also made all NOPs single instructions and removed the special atomic nop.
