On Mon, Jan 15, 2018 at 07:59:37PM +0100, Borislav Petkov wrote:
> Right,
>
> I've been putting away extending struct alt_instr for a long time now,
> trying to be conservative about it but I guess this might be the right
> time to change that. How about:
>
> struct alt_instr {
> s32 instr_offset; /* original instruction */
> s32 repl_offset; /* offset to replacement instruction */
> u16 cpuid; /* cpuid bit set for replacement */
> u8 instrlen; /* length of original instruction */
> u8 replacementlen; /* length of new instruction */
> u8 padlen; /* length of build-time padding */
> u64 flags; /* alternative flags, see <some enum> */
> } __packed;
>
> This way we have 64 settings. So we could do:
>
> ...
> .flags = ALT_FLAGS_STATIC_CPU_HAS,
>
> or something like that and then we can do additional processing/matching
> for the alternatives.
>
> Or, we can do
>
> struct alt_instr {
> s32 instr_offset; /* original instruction */
> s32 repl_offset; /* offset to replacement instruction */
> u16 cpuid; /* cpuid bit set for replacement */
> u8 instrlen; /* length of original instruction */
> u8 replacementlen; /* length of new instruction */
> u8 padlen; /* length of build-time padding */
> u8 type; /* types */
> } __packed;
>
> and have 256 types but that would be limiting as we won't be able to set
> more than one.
>
> Hmmm?
That might be a good idea, but here we also need to annotate jump
labels. So unless you want to make alternatives broad enough to
encompass jump labels, I don't think it solves this particular problem.
--
Josh
