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SubjectRe: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions

+arm64 people...

On Mon, Mar 28, 2022 at 10:14:38PM +0200, Peter Zijlstra wrote:
> On Mon, Mar 28, 2022 at 12:59:20PM -0700, Josh Poimboeuf wrote:
>
> > I'm not making any major changes to the code, just shuffling things
> > around to make the interface more modular. I hope to have something
> > soon (this week). Peter recently added a big feature (Intel IBT) which
> > is already in -next.
>
> Hit Linus' tree yesterday :-)
>
> > Some years ago Kamalesh Babulal had a prototype of objtool for ppc64le
> > which did the full stack validation. I'm not sure what ever became of
> > that.
>
> I've also heard chatter about s390.
>
> > FWIW, there have been some objtool patches for arm64 stack validation,
> > but the arm64 maintainers have been hesitant to get on board with
> > objtool, as it brings a certain maintenance burden. Especially for the
> > full stack validation and ORC unwinder. But if you only want inline
> > static calls and/or mcount then it'd probably be much easier to
> > maintain.
>
> IIRC the major stumbling block for arm64 is the whole jump-table thing.
> Either they need to rely on compiler plugins to provide objtool that
> data (yuck, since we support at least 2 different compilers), disable
> jump-tables (yuck, for that limits code-gen just to please a tool) or
> use DWARF (yuck, because build times).
>
> There was a little talk about an impromptu 'abi' to communicate
> jump-table details to objtool without going full on DWARF, but that
> seems to have hit a dead end again.

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