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    SubjectRe: [PATCH v3 18/26] objtool: Fix !CFI insn_state propagation
    On Tue, Mar 24, 2020 at 04:40:06PM -0500, Josh Poimboeuf wrote:
    > On Tue, Mar 24, 2020 at 04:31:31PM +0100, Peter Zijlstra wrote:

    > > + if (!save_insn->visited) {
    > > + /*
    > > + * Oops, no state to copy yet.
    > > + * Hopefully we can reach this
    > > + * instruction from another branch
    > > + * after the save insn has been
    > > + * visited.
    > > + */
    > > + if (insn == first)
    > > + return 0; // XXX
    >
    > Yeah, moving this code out to apply_insn_hint() seems like a nice idea,
    > but it wouldn't be worth it if it breaks this case. TBH I don't
    > remember if this check was for a real-world case. Might be worth
    > looking at... If this case doesn't exist in reality then we could just
    > remove this check altogether.

    I'll go run a bunch of builds with a print on it, that should tell us I
    suppose.

    > > +
    > > + WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
    > > + sec, insn->offset);
    > > + return 1;
    > > + }
    > > +
    > > + insn->state = save_insn->state;
    > > + }
    > > +
    > > + *state = insn->state;
    >
    > This would have been easier to review if apply_insn_hint() were added in
    > a separate patch.

    27 it will be!

    > > +
    > > + /* restore !CFI state */
    > > + state->df = old.df;
    > > + state->uaccess = old.uaccess;
    > > + state->uaccess_stack = old.uaccess_stack;
    >
    > Maybe we should just move the CFI stuff into a state->cfi substruct.
    > That would remove the need for these bits and probably also the comment
    > above the insn_state declaration.

    Indeed!

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