Messages in this thread | | | Date | Mon, 15 Jan 2018 13:08:19 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 2/4] objtool: Implement jump_assert for _static_cpu_has() |
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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
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