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    SubjectRe: [PATCH v3 18/26] objtool: Fix !CFI insn_state propagation
    On Wed, Mar 25, 2020 at 12:00:10AM +0100, Peter Zijlstra wrote:
    > On Tue, Mar 24, 2020 at 11:11:09PM +0100, Peter Zijlstra wrote:
    > > 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.
    >
    > I can a bunch of builds, including an allmodconfig with the below on top
    > and it 'works'.
    >
    > So I suppose we can remove this special case.
    >
    > ---
    > --- a/tools/objtool/check.c
    > +++ b/tools/objtool/check.c
    > @@ -2134,11 +2134,13 @@ static int apply_insn_hint(struct objtoo
    > * after the save insn has been
    > * visited.
    > */
    > - if (insn == first)
    > - return 0; // XXX
    >
    > WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
    > sec, insn->offset);
    > +
    > + if (insn == first)
    > + return -1;
    > +

    I think all the validate_branch() callers aren't prepared to handle a -1
    return code.

    We can just be lazy and remove this 'insn == first' check and consider
    it a non-fatal warning.

    --
    Josh

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