Messages in this thread | | | Date | Sun, 11 Nov 2018 12:31:25 +0100 | From | Pavel Machek <> | Subject | Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack |
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> > > > +/* > > > > + * State component 12 is Control flow Enforcement kernel states > > > > + */ > > > > +struct cet_kernel_state { > > > > + u64 kernel_ssp; /* kernel shadow stack */ > > > > + u64 pl1_ssp; /* ring-1 shadow stack */ > > > > + u64 pl2_ssp; /* ring-2 shadow stack */ > > > > +} __packed; > > > > + > > > > > > Why are these __packed? It seems like it'll generate bad code for no > > > obvious purpose. > > > > That prevents any possibility that the compiler will insert padding, although in > > 64-bit kernel this should not happen to either struct. Also all xstate > > components here are packed. > > > > They both seem like bugs, perhaps. As I understand it, __packed > removes padding, but it also forces the compiler to expect the fields > to be unaligned even if they are actually aligned.
This structure is shared with hardware, right? __packed seems like right thing to do semantically.
As x86 handles unaligned accesses automatically, there should not be much difference either way. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html [unhandled content-type:application/pgp-signature] | |