lkml.org 
[lkml]   [2018]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4] objtool: Implement jump_assert for _static_cpu_has()
On Mon, Jan 15, 2018 at 01:08:19PM -0600, Josh Poimboeuf wrote:
> 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.

Well, to clarify, it would solve _some_ of the problem. Maybe even most
of the problem. We'd still need to special-case jump labels in objtool
(like in 1/4), but that's probably not a big deal.

So, contradicting my previous answer here... yes, it would help.

--
Josh

\
 
 \ /
  Last update: 2018-01-15 20:12    [W:0.043 / U:4.680 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site