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

[Peter Zijlstra <peterz@infradead.org>]

+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.