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SubjectRe: [PATCH v3 18/26] objtool: Fix !CFI insn_state propagation
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;
+
return 1;
}

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